Buchla 200e
Encyclopedia
The Buchla 200e is a modular synthesizer
designed by electronic music pioneer Don Buchla
and built by Buchla and Associates
.
system. Many of the modules in the 200e series share similar functionality and layout with Model 200 modules, and therefore have similar names. However, all of the e series modules have the ability to store and recall parameters set by the user. Another new feature the 200e adds is MIDI implementation via the 225e MIDI Decoder module. This allows 200e modules to respond to MIDI note, velocity, and controller data via internal busses.
Discontinued 200e modules:
's ones:
But the Buchla 200e modules were not designed to fit perfectly into these categories. Rather, each module implements and crosses category boundaries according to Buchla's vision of analog synthesis. The synthesizer sound basics entry offers a helpful introduction to understanding how to compose sound. With that as background, there are two ways to think about making sounds with the 200e: the electronic view and the sonic view.
Taken together, the electronic view allows us to explore the sonic properties of networks we can construct with the hardware available, while the sonic view helps us focus on how to make the electronic connections necessary to realise a sound we have heard only in our minds.
oscillator and a principal oscillator (aka a carrier wave
). The 259e can produce two distinct audio signals (one from each type of oscillator), while the 261e can also produce a pre-processed signal in each oscillator. The pre-processed signal of the 261e modulation oscillator is presented as a sine wave (i.e., before being shaped by the variable wave shaper), whereas the pre-processed signal from the 261e principal oscillator is presented after LFO modulation but before timbral modulation. Thus the 261e can generate a total of four distinct audio signals.
As a control voltage, pitch on the 200e is represented as 1.2 V/octave
(0.1 V/semitone
). Since the 200e was designed to maintain 0.01 V accuracy, it means that tuning is within 10 cents
. If we assume that 440 Hz/A5 is 5 V (the center of the 10 V control voltage scale), then the pitch control knob ranges from 27.5 Hz/A1 through 7040 Hz/A9 (see piano key frequencies
) and voltages are as follows
There are two basic ways to control audio oscillator pitch for each oscillator, and there are differing rules for what works in what mode, but the math works something like this:
259e:
259e:
261e:
261e:
and if pitch tracking (and remote enable) is off, then each oscillator of both modules implement
By feeding MIDI pitch into the control voltage inputs it is possible to scale tuning from essentially flat (increases in MIDI pitch voltage are exactly offset by increased negative scaling of the control voltage) to 2 semitones per semitone of MIDI pitch. And with the 256e voltage control processor, additional stretch tunings can be achieved.
Pitch need not be constant, as the vibrato
entry teaches. The vibrato effect can be realized by modulating the principal oscillator with a low-frequency oscillator. The modulation oscillator of both the 259e and the 261e can be set between a range of 1/4 Hz and 64 Hz and both modules support an internal connection whereby the modulation oscillator can modulate the pitch of the principal operator by selecting the "pitch" MOD TYPE with no external cables are needed. But other LFO sources may be employed. See the Extra-Low LFO using the 281e section for information on constructing other LFOs.
Pitch need also not also be constant as the portamento
entry teaches. It would be wonderful if portamento were an intrinsic function of the 225e MIDI controller, not least because it would have the benefit of stable and reliable pitch. See the Portamento using the 266e and 256e entry in the Neat tricks section for details on how to work around this apparent limitation.
is next. The modulation oscillator of the 259e offers three basic wave shapes: falling sawtooth
, square
, and triangle
. As audio signals (the "hi" range of the modulation oscillator), these shapes have the timbre of a bowed violin string (sawtooth), a classic synth lead (square), and a woodwind instrument such as a clarinet (triangle).
The principal oscillator of the 259e offers far more variety: a sine wave
is used to drive two digital wave tables, which are called "red" and "green". The "morph" voltage pans between the two tables and the "warp" voltage controls the amplitude of the sine wave that drives the tables. (In Keyboard Magazine Jim Aikin's review of the 200e claims that warp produces higher overtones by sweeping more of the digital wavetable.) In both the red and the green tables, the first wave table is a simple sine wave (meaning that what goes in is what comes out, and that increasing the amplitude of the driving wave merely increases the amplitude of the resulting output wave). But waves 2 through 8 are different between red and green, and each one offers a palette of unique timbres. Moreover, it appears that the higher the warp factor the more high harmonic content is present in the resulting waveform. TODO: build a table of screenshots using xoscope images. TODO: Identify which Buchla wave sequence looks like the Shaper sequence of the K2600. Who is copying whom?
Because the 259e uses digital wave tables, the output waves exhibit aliasing when used at frequencies above their nominal frequency. Another source of aliasing can come from the way the oscillators are synchronized. When synchronized to MIDI note events, the oscillator waveform resets to its initial state when a note on event is received. If the waveform was near the peak of its amplitude when the note on event arrives, one may hear an audible "click" as the waveform resets to zero. (Such momentary aliasing can be eliminated by running the signal through an envelope with a non-zero attack value.) Similarly, if the modulation oscillator is synchronized to the principal oscillator using "hard sync", then every time the principal oscillator completes a full wave cycle, the modulation oscillator is reset, regardless of where it was in its wave cycle. The aliasing caused by hard sync is periodic as opposed to momentary, hence it really affects timbre (usually making it sound hard or edgy). The "soft sync" option uses a phase-locked loop to bring the modulation oscillator into step with the principal oscillator without an abrupt discontinuity (or audible aliasing). The point is: among other factors, timbre is affected by aliasing effects. Caveat approximator.
The 259e has a special internal connection between the modulation oscillator and the principal oscillator. This connection is established by selecting one or more MOD TYPE connections and then adjusting the MODULATION INDEX (which seems to be another way of saying modulation amplitude). When the MOD TYPE is "freq" and the modulation oscillator runs in the audio range, the 259e acts as a dual operator FM synthesizer, albeit a very non-standard FM synthesizer. FM Synthesis is achieved by modulating the frequency of a carrier signal with a modulation signal that is harmonically related to it (usually the 1st, 2nd, or some other Nth harmonic). Sine waves present the most simple case: sine waves are fundamental tones, so the harmonic relationship between the two waves is precisely the relationship between the two fundamentals. A sawtooth, square, or triangle wave consists of a rich set of harmonics, which means that even if there is a simple harmonic relationship between the fundamental of a sawtooth modulator and a sinusoidal carrier wave, the relationship of all the other harmonics gets complicated very quickly. If the carrier wave is also a complex wave, the result is going to be "complex". Technically the 259e is capable of FM synthesis, but it is not capable of the most basic form of FM synthesis: a sine wave carrier modulated by a harmonically related sine wave. I concur with Jim Aikin that the FM synthesis using the 259e may be suitable for brash effects, but not mellow, bell-like tones.
The morphing feature of the 259e makes it particularly well suited for plucked string sounds. A wide range of bell tones is also possible using external amplitude modulation of the modulation oscillator and principal oscillator using either the 291e modulation section, or the 285e Balanced Modulator.
The original 259e is no longer on Buchla and Associate's list of currently available modules, but has been replaced (Nov 2009) with the 259e Twisted Waveform Generator. The new version reserves three of its wave tables on each bank for user adjustable memory scanning. The memory scanning settings can return anything from silence, to typical wave tables, to pitched noise.
The 261e's Timbre section has three voltage controllable parameters:
These controls allow for a wide range of voltage controllable timbres. Because the 261e's timbre processing is performed by analog circuitry, aliasing introduced by table-driven systems (like those used on the 259e) is eliminated.
The modulation oscillator offers voltage-controlled waveshaping, continuously variable from sine to pulse. It can be synchronized (with variable offset) to the principal oscillator, or to note-on MIDI messages. There are three types of internal modulation available, which may be used in any combination:
Modulation depth can controlled by manual control as well as by an invertible, attenuated CV input, but the amount is common among all three modulation types. When connecting the modulation and principal oscillators using the internal modulation bus, only the pre-processed sine wave is used, regardless of the modulation oscillator's waveshape parameter. By using this internal connection between the modulation and principal oscillator, it is possible to synthesize familiar FM synthesis tones. However, routing the modulation oscillator output signal into the "fm in" signal input of the 261e (or the 259e) externally yields different results. Instead of a pleasing FM tone, harsh artifacts begin to appear as soon as the "fm in" input knob is moved beyond zero. One work-around is to attenuate the modulation output by routing it through a 210e and attenuating the connection a few clicks below unity. Results using this method are more in line with using the internal connection.
When used in conjunction with the model 225e MIDI Manager, the 261e's pitches respond to internally routed MIDI messages. Up to four 261e's can operate in a single system, each on a private MIDI channel (set using a DIP switch on the back of the module). Because the 261e is an 'e' series module, all knob and switch settings can be stored with a 225e or 206e module.
The 260e has a "barber pole" mode in which an internal computer controls both pitch class generators. One parameter controls how rapidly the pitch changes (+/- 2.5 octaves/sec) and the other controls the number of steps per octave (from 2 to 24; 2 steps per octave are tri-tones
; 12 steps per octave is the familiar semitone
scale; 24 steps per octave are quarter-tones
). A mode setting controls whether the steps are continuous (portamento), quantized (ordered), or eccentric (randomly ordered).
The 260e can also be used to generate Shepard tone
s which are best heard when wrapped in a staccato
or marcato
envelope. Such envelopes can be created using the 281e and 292e modules as illustrated below.
The Noise section generates three flavors of noise which are called"-3 db / oct" , "flat" , and "+ 3 db / oct," which correspond to brown
, pink
and white
noise.
The Fluctuating Random section outputs a smooth random voltage that has a probable rate of change. This can be thought of as an LFO that has a frequency, but a smooth random waveform. The rate of change can be voltage controlled.
The Quantized Random section provides two stepped outputs. Each of the two outputs has a corresponding pulse input. When a pulse is received a random voltage between 0 and 10 volts is selected, out of the selected number of states. There are a variety of random distributions that can be utilized. For example, if the "number of states" control is set to 2, the only possible output values are 0 or 10 volts, and one of these two values will be selected based on the selected distribution. If the number of states control is set to 3, there are three possible values: 0, 5 volts, and 10 volts. The maximum number of states is twenty four, and this parameter can be voltage controlled.
The Stored Random Voltage section also has two outputs and two pulse input jacks. There are three parameters: skew, degree, and chaos, all of which can be voltage controlled. With degree and chaos turned all the way down, this section acts like a "traditional" Sample and Hold. The voltage from the skew jack and knob is sampled at every input pulse. Degree and chaos control how much randomness is added to the skew voltage, and the amount of feedback involved, which narrows the range of any given random jump.
In his pioneering work, Vladimir Ussachevsky
established the concept of an envelope composed of Attack, Decay, Sustain, and Release (or ADSR). The 281e Quad Function Generator makes it possible to create a variety of envelope models. To create a classic ADSR with individual control over each component, two Function Generators can be coupled as follows:
The A OR B (resp. C OR D) output is the ADSR envelope function, and is driven by a pulse delivered to the A or B (resp. C or D) input.
For the special case where the sustain level equals the attack peak (such as a pipe organ, i.e., there's no decay between attack and sustain), the sustain input mode suffices directly and no complex hookup is needed.
Similarly, for the special case where there is no sustain, just attack and release (such as an acoustic guitar), the impulse input suffices directly.
The Quadrature Mode, generators A and B (resp. C and D) operate in tandem as follows:
One use of quadrature mode is to implement delayed attack and delayed release (with the A (resp. C) generator implementing the delay parameters and the B (resp. D) generator providing the delayed attack and delayed decay envelopes).
It is important to note that the Quad Function Generator operates solely on control voltages--they do not, themselves, alter the dynamics of an audio signal. To do this, the 292e Quad Dynamics Manager is needed. In its simplest mode as a VCA
, this module controls the signal level of four separate audio signals (plus a mix of all four signals if that's useful) based on three separate control voltage parameters: a level parameter (such as the output of a Function Generator), an optional Velocity parameter (typically taken from the 225e MIDI Decoder), and a knob setting that can range from full off to full on (in which case the signal passes through unchanged). Thus, with three modules (or four if you want to decode MIDI notes into control voltage signals), one generating a tone, one generating an envelope, and one applying the envelope to the tone, we have the basics of an analog synthesizer than can play notes, albeit one at a time.
It should also be obvious that we can implement tremolo
by feeding the output of an LFO into either the level or velocity input of one of the Quad Dynamics control voltage input. Since control voltages sum when banana plugs are combined, tremolo can be added to circuits that already have both level and velocity assigned without using an additional dynamics control circuit.
Each stage stores two control voltages plus a time constant. Values are adjusted using a parallel array of potentiometers: large knobs to set voltages, and small knobs to set time constants. A push button selects the output affected by the voltage knobs. Each stage also has two programmable pulse outputs, and an 'All' pulse output. Pulses are generated as the sequencer moves from stage to stage. Current stage number is indicated with a circular array of orange LEDs; edit position is indicated with blue LEDs. Both voltage and time constants change as the knob is turned, whether the 250e is playing or not. Editing can be performed while the 250e is in operation.
In edit mode, the voltage range can be selected from among 0-2, 2-4, 4-6, 6-8, 8-10, or all (0-10) Volts. In addition, recent versions of the software add a seventh choice (No range LEDs lit) where the voltage output is proportional to the stage number. This can be useful for synchronizing two 250e's in conjunction with strobed or continuous mode.
Control voltages may be individually interpolated, quantized, or replaced with external voltages (A, B, C, or D) for each stage. When interpolation is selected for a stage, the 250e will interpolate between knob positions, a knob position and an external input or between two external inputs. Stages can be set to loop, or jump to another stage. When looping, a count can be set for the loop, including 'infinite', and loops may be nested. Stages may also be selected directly using one of two stage address modes:
As with voltages, time constants may be individually, quantized, or replaced with external voltages. In addition to the voltage CV outs, there is a third CV out, proportional to the time knob for each stage. The time 'interpolation' option only affects the time CV out and does not affect the time constants. The 'Time' CV input affects the duration of all stages, and can be adjusted with the Time Mult knob. When the knob is turned to the left, greater voltages will slow down the sequence; turned to the right they will speed up the sequence. The 'Time Output' CV may be externally patched to the 'Time Input' CV for self-modulation of time constants.
Because the 250e is part if the 'e' series of modules, settings can be stored and recalled using a 225e MIDI Decoder/Preset Manager.
A multiplier between negative one and one scales the input voltage. Because the control signals in the 200e are unipolar (always positive), a constant offset is applied to prevent negative output when the multiplier is negative:
.
The constant offset prevents the 255 from being used to attenuate an inbound signal to zero. As the inbound signal is attenuated, the output approaches the halfway point of five volts. At full attenuation of the input, the output is a constant five volts. There are however certain unattenuated destinations in the 200e that benefit from this convention because they are often operated around a 50% offset (e.g. 281e decay, and 206e pan). Further, the offset can be readily tuned out in some destinations (e.g. continuous stage address on the 250e).
The 255 can be used as a source of constant DC voltage between zero and ten volts. With the input disconnected, turning the multiplier knob provides the desired result on the output.
The 255 module is incredibly useful for portamento, where one would expect a glide spanning two octaves to take twelve times longer than a glide between a wholetone. By having two separate lag times, one for rising voltages and one for falling voltages, one can make synth patches that slowly climb to their expected pitches, but which, on descent, track notes without perceptible portamento. Or vice-versa.
The 255 is useful as an envelope generator. For certain pulses in the 200e system, namely those available from the 250e, a zero attack setting and a nonzero decay setting on the 255 will result in an envelope output. Envelopes created this way vary according to the rate of incoming triggers, and the results are sonically useful.
, something as intrinsic to audio tone as color is to light. We have already discussed using modules to create tones that have an initial timbre. And we have talked about carving notes from tones by using envelopes. We will now talk about carving "that sound" from timbre.
In the documentary film Moog (film)
, Robert Moog
talks about one of the greatest influences of the synthesizer on modern music: the sound of "wow" (say it slowly, w-o-w). The sound of "wow" (or wah-wah) is perhaps the most cliched timbric modulation. It can be synthesized by applying a bandpass filter to a harmonically rich tone such as a sawtooth wave (sine waves need not apply!) and moving it from 200 Hz to 1000 Hz and back again. With the right filter parameters and the right envelopes driving the filters, we can perceive the production of a dynamic, shifting formant
. This effect, which sounds almost linguistic, suddenly imparts a whole new dimension to the way we interpret the tone. Time-dependent filter modulation is what makes the guitar of Jimi Hendrix
"open up" in the song Foxy Lady
, or throb in the hands of Eric Clapton
in the song Sunshine of Your Love
.
To make the transition smooth and still distinct, stages can be broken into two phases, a stable phase and a morphing phase. If we want the morph in the previous example to take place in the time of a 1/16 note, the four stages would be
The 291e also supports frequency modulation of each input which makes it possible to build both simple and complex FM operators. The fm circuit of the 291e is different than that of the 259e and 261e and less prone to aliasing. Combined with a 210e, the 291e supports the following FM algorithm constructs:
Thus a 291e can be a powerful FM workstation independent of its filtering abilities.
and a high-pass filter
. Consider the square wave
which theoretically has an infinite number of only odd-order harmonics. If we want to "soften" the sound, we need to remove all the higher-order harmonics above whatever frequency we perceive as "harsh". For example, let's say that harmonics above 2.2 kHz are objectionable. For a square wave at A5, that's the 5th harmonic and above. For a square wave at A3, that's the 7th harmonic and above. For a square wave at A6, that's the 3rd harmonic and above. A low-pass filter can uniformly remove all offending high-frequency signals regardless of whether they are the 7th, 11th, or 13th harmonics, creating a greater consistency of tone than merely saying "let's just compose a wave consisting of the 1st, 3rd, and 5th harmonics", which gets it wrong for the higher registers.
The signal chain of the 292e Quad Dynamics Manager has a voltage-controlled low-pass filter that can operate in tandem with or instead of the VCA (aka gate). There appears to be no way to control the slope of the low-pass filter; it is fixed at 12db/octave. A popular enhancement to low-pass filters is resonance, which compensates (or overcompensates) for signal attenuation at the cutoff frequency. Since a resonant peak overlaid on a low-pass filter sounds a lot like a band-pass filter with some extra mojo, resonant low-pass filters have formant-forming qualities. The 292e does not support a resonance parameter, but the signal from a 292e can be added to a band-passed signal from a 291e to create a similar effect. FIXME: how do we tune the two different modules so that we know the resonant peak and the low pass filter are really in agreement? FIXME: is there some trick way to combine the two audio signals without burning a column of the 210e?
One way to achieve the effect of a high pass filter, other than possibly the warp control of the 259e and the timbre control of the 261e, is to mix together a lopass filtered signal with the original signal, with one of them inverted in polarity. On the 200e, the only proven phase inverter is the submixer of the 227e, and then only the signal added via the "In The Mix" switch is inverted. There is no evidence that the 210e nor the accessible submixer outputs of the 227e are inverting.
If I'm wrong and the 292e just implements a first-order filter, the above will give the effect of a second-order filter and all four units will need to be connected to implement a fourth-order filter.
a portamento effect by using the 266e Source of Uncertainty in a certain way. The basic idea is simple: since portamento is a glide between one pitch and another, we need a way to capture a pitch so that when a new pitch is played we can glide from the original pitch to the new target pitch. We do this by configuring the Stored Random Voltages section of the 266e as a Sample-and-Hold function: set "skew" to the leftmost position and connect the voltage to be sampled to the CV input for "skew". Set "degree" and "chaos" to zero. The output of the Sample-and-Hold function is our original note (sort of) and the current MIDI pitch (as a control voltage) is the target pitch. To glide from one to the other, we put the two pitch voltages into the two source inputs of a 256e Control Voltage Processor circuit and use the output of a 281e Quad Function Generator to pan from the original pitch to the new pitch. The Attack parameter of the 281e defines the glide speed.
The pulse network is a bit tricky: the MIDI note on pulse triggers the 281e envelope, which is configured in transient mode. The output of the 281e drives not only the selection logic of the 256e, but also a second circuit in the 256e. This second circuit is configured to generate a pulse at the end of the attack phase by using a breakpoint function (in value = 8 V, out value = 0 V). The output of this second circuit drives the "update" input of the 266e. The 281e produces a pulse at the end of the decay phase of the envelope, but that is too late: we need to sample the pitch before the decay, else our selection logic will drop back to the initial pitch and we'll hear a glitch. By sampling the pitch just as we reach the top, there won't be a glitch when the 281e envelope decays and the first 256e circuit switches back from MIDI pitch to sampled pitch.
Would that it were so simple! For reasons I do not yet understand, the 266e flattens out voltages, which has the effect of changing an octave scale into something not quite an octave. If it stretched pitch instead of shrinking it we could fix the problem with a single 256e circuit. This is because we could raise the Output @ 0 V, lower the Output @ 10 V, creating a transfer function of something like 0.8:1 and the product of the two would be a nice 1:1 transfer function. Since the incoming scale is flattened, we need a transfer function that's more like 1.25:1, and that requires two 256e circuits. The first circuit uses a breakpoint function to produce 10 V at approx 8 V input. The second circuit uses a breakpoint function to produce 0 V at approx 2 V input. By running these in series we get our (> 1):1 transfer function, and pitch is restored (to within perhaps 20 cents, because all these pitch transformations add up their pitch errors). The output of the corrected sample pitch is the actual input we use for the 256e selection circuit, not the output of the 266e directly.
Of course we can also use this portamento method to drive the frequency of a 291e or 292e filter to get the classic ELP
effect of a glide opening up with a big "BWAHH!" at the finish.
n.b. It is also possible to save two 256e circuits by doing the following. By using two separate pitch busses on the 225e unit we can tune the offset of each separately. Let's call the first bus the Hold bus (used to feed the 266e Sample-and-Hold circuit) and the second bus the Now bus (the pitch currently being played). By using a 210e CV circuit, we can flatten the pitch of the Now bus so it has exactly the same slope as the output of the 266e (which is fed by, but is not itself, the Hold bus). Tuning the offsets of the two pitches helps set the slope correctly across a range of notes. Now that both inputs to the poramento selector circuit behave the same for a given pitch, we can correct the flat slop by using a breakpoint function. By setting the breakpoint out value to zero and setting the in value to around 2 V, we create a slope that is greater than unity, offsetting the less-than-unity slop of the 266e and the intentionally less-than-unity 210e output. We tune the 256e circuit until the slope of the breakpoint function cancels out the slopes of the input functions and now we can feed the CV output to the CV input of an oscillator like the 261e, tune it to 1.2 V/octave and we're good to go. It's a good idea to conserve 256e circuits because they can be useful for other things...
To calculate the difference between two notes we need two circuits of the 256e and a summing circuit from the 210e. The first 256e circuit is configured as a negative transfer function giving us 10 V - P1 for an input of P1. We use the 210e to add (10 V - P1) /2 with P2/2, giving 5 V + (P2 - P1) /2 and feed this output to the input of the second 256e circuit. The second 256e circuit is configured as a non-linear transfer function that looks like the letter V. I.e., it gives 10 V - 2*Vin when Vin <= 5 V and 2*Vin - 10 when Vin > 5 V. When P1 is near P2, then 5 V + P2 - P1 is near 5 V and the non-linear transformation gives us a value near 0 V, a very short time for the portamento glide time. When P1 is two octaves (2.4 V) less than P2, then 5 V + P2 - P1 is 7.4 V and the non-linear transformation gives us 14.8 V - 10 V or 4.8 V, a good amount of glide time. Similarly when P1 is two octaves above P2 (2.4 V), then 5 V + P2 - P1 is 2.6 V and the non-linear transformation gives us 10 V - 5.2 V = 4.8 V, an equally good amount of glide time. In either case, the 4.8 V can be multiplied by the attack time of the 281e unit to get the right amount of portamento time.
This setup uses 3 210e inputs, 4 256e circuits, 1 266e input in the Stored Random Voltages section, 1 281e envelope generator circuit, and 2-3 MIDI pitch outputs of a 225e circuit, not including the number of oscillators, evelope generators, filters, and VCAs needed to generate a sound.
Modular synthesizer
The modular synthesizer is a type of synthesizer consisting of separate specialized modules connected by wires to create a so-called patch. Every output generates a signal – an electric voltage of variable strength...
designed by electronic music pioneer Don Buchla
Don Buchla
Don Buchla is a pioneer in the field of sound synthesizers, releasing his first units months after Robert Moog's first synthesizers...
and built by Buchla and Associates
Buchla
Buchla & Associates, Inc. is a manufacturer of electronic musical instruments, notably synthesizers and unique MIDI controllers. The 200e Electric Music Box and Lightning III are currently in production.-Buchla Music Box :...
.
History
The 200e is based on the earlier Model 200Buchla 200 series Electric Music Box
The Buchla 200 series Electric Music Box is an electronic musical instrument manufactured by Buchla & Associates in Berkeley, California from 1970-1982. It is a modular analog system consisting of a collection of individual modules...
system. Many of the modules in the 200e series share similar functionality and layout with Model 200 modules, and therefore have similar names. However, all of the e series modules have the ability to store and recall parameters set by the user. Another new feature the 200e adds is MIDI implementation via the 225e MIDI Decoder module. This allows 200e modules to respond to MIDI note, velocity, and controller data via internal busses.
Modules
Currently available 200e modules:- 206e Mixer / Preset Manager
- 207e Mixer / Mic Preamplifier
- 210e Control and Signal Router
- 222e Multi Dimensional Kinesthetic Input Port
- 223e Tactile Input Port
- 225e MIDI Decoder / Preset Manager
- 227e System Interface
- 230e Triple Envelope Tracker / Preamplifier
- 250e Arbitrary Function Generator
- 256e Quad Control Voltage Processor
- 259e Twisted Waveform Generator
- 260e Duophonic Pitch Class Generator
- 261e Complex Waveform Generator
- 266e Source of Uncertainty
- 281e Quad Function Generator
- 285e Frequency Shifter / Balanced Modulator
- 291e Triple Morphing Filter
- 292e Quad Dynamics Manager
- 296e Spectral Processor
Discontinued 200e modules:
Theory
The 200e synthesizer platform includes several modules that roughly correspond to the canonical analog synthesizerAnalog synthesizer
An analog or analogue synthesizer is a synthesizer that uses analog circuits and analog computer techniques to generate sound electronically. The earliest analog synthesizers in the 1920s and 1930s such as the Trautonium were built with a variety of vacuum-tube and electro-mechanical technologies...
's ones:
- Voltage-controlled oscillatorVoltage-controlled oscillatorA voltage-controlled oscillator or VCO is an electronic oscillator designed to be controlled in oscillation frequency by a voltage input. The frequency of oscillation is varied by the applied DC voltage, while modulating signals may also be fed into the VCO to cause frequency modulation or phase...
: 259e, 260e, 261e - Voltage-controlled filterVoltage-controlled filterA voltage-controlled filter is a filter whose operating characteristics can be controlled by means of a control voltage applied to one or more inputs...
: 291e, 292e, 297, 296e - Voltage-controlled amplifier: 227e, 292e
- Musical KeyboardMusical keyboardA musical keyboard is the set of adjacent depressible levers or keys on a musical instrument, particularly the piano. Keyboards typically contain keys for playing the twelve notes of the Western musical scale, with a combination of larger, longer keys and smaller, shorter keys that repeats at the...
: 222e, 223e - Envelope generator: 225e, 249e, 250e, 281e
- Control Voltage: 266e, 255, 256e
- Low frequency oscillator: 259e, 261e, 266e, 281e
- Phase shifter: 297,
- Ring modulator: 285e
- SequencerMusic sequencerThe music sequencer is a device or computer software to record, edit, play back the music, by handling note and performance information in several forms, typically :...
: 249e, 250e - MixerMixing consoleIn professional audio, a mixing console, or audio mixer, also called a sound board, mixing desk, or mixer is an electronic device for combining , routing, and changing the level, timbre and/or dynamics of audio signals. A mixer can mix analog or digital signals, depending on the type of mixer...
: 206e, 207e, 210e, 227e, 292e
But the Buchla 200e modules were not designed to fit perfectly into these categories. Rather, each module implements and crosses category boundaries according to Buchla's vision of analog synthesis. The synthesizer sound basics entry offers a helpful introduction to understanding how to compose sound. With that as background, there are two ways to think about making sounds with the 200e: the electronic view and the sonic view.
- The electronic view represents three networks: the audio network (which results in the ultimate audio signal that is actually heard), the continuous control voltage network (where voltages ranging from zero to 10 volts DC represent the full scale of all parametric values), and the pulse network (which conveys transient and sustain information).
- The sonic view is that sound is perceived as having a characteristic pitch (or not in the case of noise), a characteristic timbre, and a characteristic sound that notes have when played and released. This view can be represented as a sonic pipeline that starts with an oscillator (or noise) feeding a filter (timbre) contained in an envelope (attack, decay, sustain, and release or ADSR).
Taken together, the electronic view allows us to explore the sonic properties of networks we can construct with the hardware available, while the sonic view helps us focus on how to make the electronic connections necessary to realise a sound we have heard only in our minds.
Creating audio tones
Since both views begin with an oscillator, we will begin with a description of the primary modules for generating an initial pitch and timbre, the 259e and the 261e Complex Waveform Generator. Both the 259e and the 261e have two oscillators: a modulationModulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...
oscillator and a principal oscillator (aka a carrier wave
Carrier wave
In telecommunications, a carrier wave or carrier is a waveform that is modulated with an input signal for the purpose of conveying information. This carrier wave is usually a much higher frequency than the input signal...
). The 259e can produce two distinct audio signals (one from each type of oscillator), while the 261e can also produce a pre-processed signal in each oscillator. The pre-processed signal of the 261e modulation oscillator is presented as a sine wave (i.e., before being shaped by the variable wave shaper), whereas the pre-processed signal from the 261e principal oscillator is presented after LFO modulation but before timbral modulation. Thus the 261e can generate a total of four distinct audio signals.
As a control voltage, pitch on the 200e is represented as 1.2 V/octave
Octave
In music, an octave is the interval between one musical pitch and another with half or double its frequency. The octave relationship is a natural phenomenon that has been referred to as the "basic miracle of music", the use of which is "common in most musical systems"...
(0.1 V/semitone
Semitone
A semitone, also called a half step or a half tone, is the smallest musical interval commonly used in Western tonal music, and it is considered the most dissonant when sounded harmonically....
). Since the 200e was designed to maintain 0.01 V accuracy, it means that tuning is within 10 cents
Cent (music)
The cent is a logarithmic unit of measure used for musical intervals. Twelve-tone equal temperament divides the octave into 12 semitones of 100 cents each...
. If we assume that 440 Hz/A5 is 5 V (the center of the 10 V control voltage scale), then the pitch control knob ranges from 27.5 Hz/A1 through 7040 Hz/A9 (see piano key frequencies
Piano key frequencies
This is a virtual keyboard showing the absolute frequencies in hertz of the notes on a modern piano in twelve-tone equal temperament, with the 49th key, the fifth A , tuned to 440 Hz...
) and voltages are as follows
- A1 is 5 V - 4.8 V = 0.2 V
- A2 is 5 V - 3.6 V = 1.4 V
- A3 is 5 V - 2.4 V = 2.6 V
- A4 is 5 V - 1.2 V = 3.8 V
- A5 is 5 V
- A6 is 5 V + 1.2 V = 6.2 V
- A7 is 5 V + 2.4 V = 7.4 V
- A8 is 5 V + 3.6 V = 8.6 V
- A9 is 5 V + 4.8 V = 9.8 V
There are two basic ways to control audio oscillator pitch for each oscillator, and there are differing rules for what works in what mode, but the math works something like this:
259e:
259e:
261e:
261e:
and if pitch tracking (and remote enable) is off, then each oscillator of both modules implement
By feeding MIDI pitch into the control voltage inputs it is possible to scale tuning from essentially flat (increases in MIDI pitch voltage are exactly offset by increased negative scaling of the control voltage) to 2 semitones per semitone of MIDI pitch. And with the 256e voltage control processor, additional stretch tunings can be achieved.
Pitch need not be constant, as the vibrato
Vibrato
Vibrato is a musical effect consisting of a regular, pulsating change of pitch. It is used to add expression to vocal and instrumental music. Vibrato is typically characterised in terms of two factors: the amount of pitch variation and the speed with which the pitch is varied .-Vibrato and...
entry teaches. The vibrato effect can be realized by modulating the principal oscillator with a low-frequency oscillator. The modulation oscillator of both the 259e and the 261e can be set between a range of 1/4 Hz and 64 Hz and both modules support an internal connection whereby the modulation oscillator can modulate the pitch of the principal operator by selecting the "pitch" MOD TYPE with no external cables are needed. But other LFO sources may be employed. See the Extra-Low LFO using the 281e section for information on constructing other LFOs.
Pitch need also not also be constant as the portamento
Portamento
Portamento is a musical term originated from the Italian expression "portamento della voce" , denoting from the beginning of the 17th century a vocal slide between two pitches and its emulation by members of the violin family and certain wind instruments, and is sometimes used...
entry teaches. It would be wonderful if portamento were an intrinsic function of the 225e MIDI controller, not least because it would have the benefit of stable and reliable pitch. See the Portamento using the 266e and 256e entry in the Neat tricks section for details on how to work around this apparent limitation.
259e Twisted Waveform Generator (f. Complex Waveform Generator)
Once pitch has been established, timbreTimbre
In music, timbre is the quality of a musical note or sound or tone that distinguishes different types of sound production, such as voices and musical instruments, such as string instruments, wind instruments, and percussion instruments. The physical characteristics of sound that determine the...
is next. The modulation oscillator of the 259e offers three basic wave shapes: falling sawtooth
Sawtooth wave
The sawtooth wave is a kind of non-sinusoidal waveform. It is named a sawtooth based on its resemblance to the teeth on the blade of a saw....
, square
Square wave
A square wave is a kind of non-sinusoidal waveform, most typically encountered in electronics and signal processing. An ideal square wave alternates regularly and instantaneously between two levels...
, and triangle
Triangle wave
A triangle wave is a non-sinusoidal waveform named for its triangular shape.Like a square wave, the triangle wave contains only odd harmonics...
. As audio signals (the "hi" range of the modulation oscillator), these shapes have the timbre of a bowed violin string (sawtooth), a classic synth lead (square), and a woodwind instrument such as a clarinet (triangle).
The principal oscillator of the 259e offers far more variety: a sine wave
Sine wave
The sine wave or sinusoid is a mathematical function that describes a smooth repetitive oscillation. It occurs often in pure mathematics, as well as physics, signal processing, electrical engineering and many other fields...
is used to drive two digital wave tables, which are called "red" and "green". The "morph" voltage pans between the two tables and the "warp" voltage controls the amplitude of the sine wave that drives the tables. (In Keyboard Magazine Jim Aikin's review of the 200e claims that warp produces higher overtones by sweeping more of the digital wavetable.) In both the red and the green tables, the first wave table is a simple sine wave (meaning that what goes in is what comes out, and that increasing the amplitude of the driving wave merely increases the amplitude of the resulting output wave). But waves 2 through 8 are different between red and green, and each one offers a palette of unique timbres. Moreover, it appears that the higher the warp factor the more high harmonic content is present in the resulting waveform. TODO: build a table of screenshots using xoscope images. TODO: Identify which Buchla wave sequence looks like the Shaper sequence of the K2600. Who is copying whom?
Because the 259e uses digital wave tables, the output waves exhibit aliasing when used at frequencies above their nominal frequency. Another source of aliasing can come from the way the oscillators are synchronized. When synchronized to MIDI note events, the oscillator waveform resets to its initial state when a note on event is received. If the waveform was near the peak of its amplitude when the note on event arrives, one may hear an audible "click" as the waveform resets to zero. (Such momentary aliasing can be eliminated by running the signal through an envelope with a non-zero attack value.) Similarly, if the modulation oscillator is synchronized to the principal oscillator using "hard sync", then every time the principal oscillator completes a full wave cycle, the modulation oscillator is reset, regardless of where it was in its wave cycle. The aliasing caused by hard sync is periodic as opposed to momentary, hence it really affects timbre (usually making it sound hard or edgy). The "soft sync" option uses a phase-locked loop to bring the modulation oscillator into step with the principal oscillator without an abrupt discontinuity (or audible aliasing). The point is: among other factors, timbre is affected by aliasing effects. Caveat approximator.
The 259e has a special internal connection between the modulation oscillator and the principal oscillator. This connection is established by selecting one or more MOD TYPE connections and then adjusting the MODULATION INDEX (which seems to be another way of saying modulation amplitude). When the MOD TYPE is "freq" and the modulation oscillator runs in the audio range, the 259e acts as a dual operator FM synthesizer, albeit a very non-standard FM synthesizer. FM Synthesis is achieved by modulating the frequency of a carrier signal with a modulation signal that is harmonically related to it (usually the 1st, 2nd, or some other Nth harmonic). Sine waves present the most simple case: sine waves are fundamental tones, so the harmonic relationship between the two waves is precisely the relationship between the two fundamentals. A sawtooth, square, or triangle wave consists of a rich set of harmonics, which means that even if there is a simple harmonic relationship between the fundamental of a sawtooth modulator and a sinusoidal carrier wave, the relationship of all the other harmonics gets complicated very quickly. If the carrier wave is also a complex wave, the result is going to be "complex". Technically the 259e is capable of FM synthesis, but it is not capable of the most basic form of FM synthesis: a sine wave carrier modulated by a harmonically related sine wave. I concur with Jim Aikin that the FM synthesis using the 259e may be suitable for brash effects, but not mellow, bell-like tones.
The morphing feature of the 259e makes it particularly well suited for plucked string sounds. A wide range of bell tones is also possible using external amplitude modulation of the modulation oscillator and principal oscillator using either the 291e modulation section, or the 285e Balanced Modulator.
The original 259e is no longer on Buchla and Associate's list of currently available modules, but has been replaced (Nov 2009) with the 259e Twisted Waveform Generator. The new version reserves three of its wave tables on each bank for user adjustable memory scanning. The memory scanning settings can return anything from silence, to typical wave tables, to pitched noise.
261e Complex Waveform Generator
The 261e is the current Complex Waveform Generator in the 'e' series of modules. Based on the original 259 from the 1970s, the 261e utilizes analog waveshaping techniques combined with digital oscillator cores, and contains two voltage controlled oscillators: a principal oscillator and a modulation oscillator. The principal oscillator has a voltage-controllable Timbre section, and the modulation oscillator offers waveshaping capabilities. Each oscillator provides an independent output plus a sine wave output, which means "classic" FM synthesis can be accomplished using the 261e.The 261e's Timbre section has three voltage controllable parameters:
- Timbre (adds harmonic content as value increases)
- High Order (shifts emphasis towards high frequencies)
- Symmetry (increases the rising edge of a wave without affecting the falling edge)
These controls allow for a wide range of voltage controllable timbres. Because the 261e's timbre processing is performed by analog circuitry, aliasing introduced by table-driven systems (like those used on the 259e) is eliminated.
The modulation oscillator offers voltage-controlled waveshaping, continuously variable from sine to pulse. It can be synchronized (with variable offset) to the principal oscillator, or to note-on MIDI messages. There are three types of internal modulation available, which may be used in any combination:
- Pitch (linear frequency modulation)
- Amplitude (including ring modulation)
- Timbre
Modulation depth can controlled by manual control as well as by an invertible, attenuated CV input, but the amount is common among all three modulation types. When connecting the modulation and principal oscillators using the internal modulation bus, only the pre-processed sine wave is used, regardless of the modulation oscillator's waveshape parameter. By using this internal connection between the modulation and principal oscillator, it is possible to synthesize familiar FM synthesis tones. However, routing the modulation oscillator output signal into the "fm in" signal input of the 261e (or the 259e) externally yields different results. Instead of a pleasing FM tone, harsh artifacts begin to appear as soon as the "fm in" input knob is moved beyond zero. One work-around is to attenuate the modulation output by routing it through a 210e and attenuating the connection a few clicks below unity. Results using this method are more in line with using the internal connection.
When used in conjunction with the model 225e MIDI Manager, the 261e's pitches respond to internally routed MIDI messages. Up to four 261e's can operate in a single system, each on a private MIDI channel (set using a DIP switch on the back of the module). Because the 261e is an 'e' series module, all knob and switch settings can be stored with a 225e or 206e module.
260e Duophonic Pitch Class Generator
The 260e generates its tones at all octaves, thus an "A" on the 260e generates sine waves at 27.5 Hz (A1), 55 Hz (A2), 110 Hz (A3), 220 Hz (A4), 440 Hz (A5), 880 Hz (A6), 1760 Hz (A7), 3520 Hz (A8), and 7040 Hz (A9). The timbre of such a tone sounds very much like a pipe organ with all ranks open.The 260e has a "barber pole" mode in which an internal computer controls both pitch class generators. One parameter controls how rapidly the pitch changes (+/- 2.5 octaves/sec) and the other controls the number of steps per octave (from 2 to 24; 2 steps per octave are tri-tones
Tritone
In classical music from Western culture, the tritone |tone]]) is traditionally defined as a musical interval composed of three whole tones. In a chromatic scale, each whole tone can be further divided into two semitones...
; 12 steps per octave is the familiar semitone
Semitone
A semitone, also called a half step or a half tone, is the smallest musical interval commonly used in Western tonal music, and it is considered the most dissonant when sounded harmonically....
scale; 24 steps per octave are quarter-tones
Quarter tone
A quarter tone , is a pitch halfway between the usual notes of a chromatic scale, an interval about half as wide as a semitone, which is half a whole tone....
). A mode setting controls whether the steps are continuous (portamento), quantized (ordered), or eccentric (randomly ordered).
The 260e can also be used to generate Shepard tone
Shepard tone
A Shepard tone, named after Roger Shepard, is a sound consisting of a superposition of sine waves separated by octaves. When played with the base pitch of the tone moving upward or downward, it is referred to as the Shepard scale. This creates the auditory illusion of a tone that continually...
s which are best heard when wrapped in a staccato
Staccato
Staccato is a form of musical articulation. In modern notation it signifies a note of shortened duration and separated from the note that may follow by silence...
or marcato
Marcato
Marcato is a musical instruction indicating a note, chord, or passage is to be played louder or more forcefully than surrounding music. The instruction may involve the word marcato itself written above or below the staff or it may take the form of an accent mark, ^ , an open vertical wedge...
envelope. Such envelopes can be created using the 281e and 292e modules as illustrated below.
266e Source of Uncertainty
The 266e Source of Uncertainty is the latest in a series of modules with this name, previous versions having model numbers 265 and 266. The 266e has four main sections: a Noise section, a Fluctuating Random Voltage section, a Quantized Random Voltage section, and a Stored Random Voltage section.The Noise section generates three flavors of noise which are called"-3 db / oct" , "flat" , and "+ 3 db / oct," which correspond to brown
Brownian noise
In science, Brownian noise , also known as Brown noise or red noise, is the kind of signal noise produced by Brownian motion, hence its alternative name of random walk noise...
, pink
Pink noise
Pink noise or 1/ƒ noise is a signal or process with a frequency spectrum such that the power spectral density is inversely proportional to the frequency. In pink noise, each octave carries an equal amount of noise power...
and white
White noise
White noise is a random signal with a flat power spectral density. In other words, the signal contains equal power within a fixed bandwidth at any center frequency...
noise.
The Fluctuating Random section outputs a smooth random voltage that has a probable rate of change. This can be thought of as an LFO that has a frequency, but a smooth random waveform. The rate of change can be voltage controlled.
The Quantized Random section provides two stepped outputs. Each of the two outputs has a corresponding pulse input. When a pulse is received a random voltage between 0 and 10 volts is selected, out of the selected number of states. There are a variety of random distributions that can be utilized. For example, if the "number of states" control is set to 2, the only possible output values are 0 or 10 volts, and one of these two values will be selected based on the selected distribution. If the number of states control is set to 3, there are three possible values: 0, 5 volts, and 10 volts. The maximum number of states is twenty four, and this parameter can be voltage controlled.
The Stored Random Voltage section also has two outputs and two pulse input jacks. There are three parameters: skew, degree, and chaos, all of which can be voltage controlled. With degree and chaos turned all the way down, this section acts like a "traditional" Sample and Hold. The voltage from the skew jack and knob is sampled at every input pulse. Degree and chaos control how much randomness is added to the skew voltage, and the amount of feedback involved, which narrows the range of any given random jump.
Creating envelopes
With the basics of how to establish initial pitch and timbre introduced, we can now look at forging our tones into notes. When using only the audio generators by themselves, we can make continuous tones that have some distinguishing characteristics. But without distinctive beginnings and endings, we cannot really call these tones notes; drones, perhaps, but not notes. To make notes we need to have beginnings and endings. This takes us to the opposite end of the audio production chain: the envelope.281e Quad Function Generator
Much of the "Buchla Sound" utilizes simple Attack Release transient envelopes, or simple Attack Sustain Release envelopes, but the more "popular" ADSR envelopes can also be generated.In his pioneering work, Vladimir Ussachevsky
Vladimir Ussachevsky
Vladimir Kirilovitch Ussachevsky was a composer, particularly known for his work in electronic music.-Biography:...
established the concept of an envelope composed of Attack, Decay, Sustain, and Release (or ADSR). The 281e Quad Function Generator makes it possible to create a variety of envelope models. To create a classic ADSR with individual control over each component, two Function Generators can be coupled as follows:
- A Attack of X milliseconds (ms)
- D Decay of Y ms
- S Sustain level of Z%
- R Release of W ms
- Set the input mode of the A (resp. C) generator to single impulse.
- Set the input mode of the B (resp. D) generator to sustained impulse.
- Set the attack of both the A and B (resp. C and D) generators to X ms.
- Set the decay of the A (resp. C) generator to Y ms.
- Set the decay of the B (resp. D) generator to W ms.
- Wire the Pulse input of the A and B (resp. C and D) generators together.
- Set the OR output level for the A OR B (resp C OR D) to Z%.
The A OR B (resp. C OR D) output is the ADSR envelope function, and is driven by a pulse delivered to the A or B (resp. C or D) input.
For the special case where the sustain level equals the attack peak (such as a pipe organ, i.e., there's no decay between attack and sustain), the sustain input mode suffices directly and no complex hookup is needed.
Similarly, for the special case where there is no sustain, just attack and release (such as an acoustic guitar), the impulse input suffices directly.
The Quadrature Mode, generators A and B (resp. C and D) operate in tandem as follows:
- When a pulse is received, A (resp. C) transitions from low to high according to its Attack parameter
- At the end of A's (resp. C's) attack, B (resp. D) transitions from low to high according to its Attack parameter
- At the end of B's (resp. D's) attack, A (resp. C) transitions from high to low according to its Decay parameter
- At the end of A's (resp. C's) decay, B (resp. D) transitions from high to low according to its Decay parameter
One use of quadrature mode is to implement delayed attack and delayed release (with the A (resp. C) generator implementing the delay parameters and the B (resp. D) generator providing the delayed attack and delayed decay envelopes).
It is important to note that the Quad Function Generator operates solely on control voltages--they do not, themselves, alter the dynamics of an audio signal. To do this, the 292e Quad Dynamics Manager is needed. In its simplest mode as a VCA
Variable-gain amplifier
A variable-gain or voltage-controlled amplifier is an electronic amplifier that varies its gain depending on a control voltage .VCAs have many applications, including audio level compression, synthesizers and amplitude modulation....
, this module controls the signal level of four separate audio signals (plus a mix of all four signals if that's useful) based on three separate control voltage parameters: a level parameter (such as the output of a Function Generator), an optional Velocity parameter (typically taken from the 225e MIDI Decoder), and a knob setting that can range from full off to full on (in which case the signal passes through unchanged). Thus, with three modules (or four if you want to decode MIDI notes into control voltage signals), one generating a tone, one generating an envelope, and one applying the envelope to the tone, we have the basics of an analog synthesizer than can play notes, albeit one at a time.
It should also be obvious that we can implement tremolo
Tremolo
Tremolo, or tremolando, is a musical term that describes various trembling effects, falling roughly into two types. The first is a rapid reiteration...
by feeding the output of an LFO into either the level or velocity input of one of the Quad Dynamics control voltage input. Since control voltages sum when banana plugs are combined, tremolo can be added to circuits that already have both level and velocity assigned without using an additional dynamics control circuit.
250e Arbitrary Function Generator
The 250e is a 16 stage function generator. It can be used to create complex envelopes or sequences of control voltages, and is the successor to the discontinued 249e.Each stage stores two control voltages plus a time constant. Values are adjusted using a parallel array of potentiometers: large knobs to set voltages, and small knobs to set time constants. A push button selects the output affected by the voltage knobs. Each stage also has two programmable pulse outputs, and an 'All' pulse output. Pulses are generated as the sequencer moves from stage to stage. Current stage number is indicated with a circular array of orange LEDs; edit position is indicated with blue LEDs. Both voltage and time constants change as the knob is turned, whether the 250e is playing or not. Editing can be performed while the 250e is in operation.
In edit mode, the voltage range can be selected from among 0-2, 2-4, 4-6, 6-8, 8-10, or all (0-10) Volts. In addition, recent versions of the software add a seventh choice (No range LEDs lit) where the voltage output is proportional to the stage number. This can be useful for synchronizing two 250e's in conjunction with strobed or continuous mode.
- It is important to note that the 250e is not controlled by MIDI: pulse inputs are used to advance/stop stages. However, pulse signals suitable for clocking the 250e may be derived from MIDI events via the 225e MIDI Decoder/Preset Manager module.
Control voltages may be individually interpolated, quantized, or replaced with external voltages (A, B, C, or D) for each stage. When interpolation is selected for a stage, the 250e will interpolate between knob positions, a knob position and an external input or between two external inputs. Stages can be set to loop, or jump to another stage. When looping, a count can be set for the loop, including 'infinite', and loops may be nested. Stages may also be selected directly using one of two stage address modes:
- In continuous mode, voltage applied to the CV input (in conjunction with knob position) will select the active output stage.
- In strobed mode, the 250e will jump to the stage selected by input voltage and knob position upon receipt of a pulse.
As with voltages, time constants may be individually, quantized, or replaced with external voltages. In addition to the voltage CV outs, there is a third CV out, proportional to the time knob for each stage. The time 'interpolation' option only affects the time CV out and does not affect the time constants. The 'Time' CV input affects the duration of all stages, and can be adjusted with the Time Mult knob. When the knob is turned to the left, greater voltages will slow down the sequence; turned to the right they will speed up the sequence. The 'Time Output' CV may be externally patched to the 'Time Input' CV for self-modulation of time constants.
Because the 250e is part if the 'e' series of modules, settings can be stored and recalled using a 225e MIDI Decoder/Preset Manager.
255 Voltage Processor
The 255 Voltage processor provides a simple way to smoothly transition from one control voltage level to another at a constant rate, independent of the voltage difference between the initial input voltage and the final output voltage. Buchla calls this a Voltage Lag Processor, and the 255 provides eight such circuits, each of which provides both a lag time for rising voltages and a lag time for falling voltages. The time marked on the panel is the time that a full voltage swing from 0 V to 10 V. For a 1 V voltage swing, the time required is 1/10 the marked amount.A multiplier between negative one and one scales the input voltage. Because the control signals in the 200e are unipolar (always positive), a constant offset is applied to prevent negative output when the multiplier is negative:
.The constant offset prevents the 255 from being used to attenuate an inbound signal to zero. As the inbound signal is attenuated, the output approaches the halfway point of five volts. At full attenuation of the input, the output is a constant five volts. There are however certain unattenuated destinations in the 200e that benefit from this convention because they are often operated around a 50% offset (e.g. 281e decay, and 206e pan). Further, the offset can be readily tuned out in some destinations (e.g. continuous stage address on the 250e).
The 255 can be used as a source of constant DC voltage between zero and ten volts. With the input disconnected, turning the multiplier knob provides the desired result on the output.
The 255 module is incredibly useful for portamento, where one would expect a glide spanning two octaves to take twelve times longer than a glide between a wholetone. By having two separate lag times, one for rising voltages and one for falling voltages, one can make synth patches that slowly climb to their expected pitches, but which, on descent, track notes without perceptible portamento. Or vice-versa.
The 255 is useful as an envelope generator. For certain pulses in the 200e system, namely those available from the 250e, a zero attack setting and a nonzero decay setting on the 255 will result in an envelope output. Envelopes created this way vary according to the rate of incoming triggers, and the results are sonically useful.
Creating complex timbre using filters
Let us now return to timbreTimbre
In music, timbre is the quality of a musical note or sound or tone that distinguishes different types of sound production, such as voices and musical instruments, such as string instruments, wind instruments, and percussion instruments. The physical characteristics of sound that determine the...
, something as intrinsic to audio tone as color is to light. We have already discussed using modules to create tones that have an initial timbre. And we have talked about carving notes from tones by using envelopes. We will now talk about carving "that sound" from timbre.
In the documentary film Moog (film)
Moog (film)
Moog is a 2004 documentary film by Hans Fjellestad about electronic instrument pioneer Dr. Robert Moog. The film features scenes of Dr. Moog interacting with various musical artists who view Moog as an influential figure in the history of electronic music....
, Robert Moog
Robert Moog
Robert Arthur Moog , commonly called Bob Moog was an American pioneer of electronic music, best known as the inventor of the Moog synthesizer.-Life:...
talks about one of the greatest influences of the synthesizer on modern music: the sound of "wow" (say it slowly, w-o-w). The sound of "wow" (or wah-wah) is perhaps the most cliched timbric modulation. It can be synthesized by applying a bandpass filter to a harmonically rich tone such as a sawtooth wave (sine waves need not apply!) and moving it from 200 Hz to 1000 Hz and back again. With the right filter parameters and the right envelopes driving the filters, we can perceive the production of a dynamic, shifting formant
Formant
Formants are defined by Gunnar Fant as 'the spectral peaks of the sound spectrum |P|' of the voice. In speech science and phonetics, formant is also used to mean an acoustic resonance of the human vocal tract...
. This effect, which sounds almost linguistic, suddenly imparts a whole new dimension to the way we interpret the tone. Time-dependent filter modulation is what makes the guitar of Jimi Hendrix
Jimi Hendrix
James Marshall "Jimi" Hendrix was an American guitarist and singer-songwriter...
"open up" in the song Foxy Lady
Foxy Lady
"Foxy Lady" is a song by The Jimi Hendrix Experience from their 1967 album Are You Experienced. It can also be found on a number of Hendrix's greatest hits compilations, including Smash Hits and Experience Hendrix: The Best of Jimi Hendrix...
, or throb in the hands of Eric Clapton
Eric Clapton
Eric Patrick Clapton, CBE, is an English guitarist and singer-songwriter. Clapton is the only three-time inductee to the Rock and Roll Hall of Fame: once as a solo artist, and separately as a member of The Yardbirds and Cream. Clapton has been referred to as one of the most important and...
in the song Sunshine of Your Love
Sunshine of Your Love
"Sunshine of Your Love" is a 1967 song by the British supergroup Cream. The song was originally released on the album Disraeli Gears in November 1967, and was later released as a single in January 1968. It is Cream's only gold-selling single in the United States. It features a distinctive...
.
291e Triple Morphing Filter
The 200e has two modules that filter audio signals: the 291e Triple Morphing Filter and the previously mentioned 292e Quad Dynamics Controller. The 291e provides three bandpass filters that can operate separately or in parallel. It also provides a summing input so that multiple 291e modules can be ganged together. Filter frequency, bandwidth, and level are each controllable via voltage. The module allows up to eight different filter "snapshots" to be defined (a mini-sequencer) which it can then "morph" over time. To achieve the rhythmic pattern of dotted-quarter/eighth note ("da-- di da-- di da--") at a 4/4 tempo of 100 bpm, two stages are needed in a loop. The duration of the first stage is 3/2 * 1 * 60 / 100 = 0.90 seconds and the duration of the second stage is 1/2 * 60 / 100 = 0.30 seconds. The morphing filter will then update the parameters from the values set in the first stage to the values set in the second stage and repeat. Transitional options allow the filter parameters to "jump" from one setting to the next, otherwise they transition smoothly ("morph") during the stage.To make the transition smooth and still distinct, stages can be broken into two phases, a stable phase and a morphing phase. If we want the morph in the previous example to take place in the time of a 1/16 note, the four stages would be
- 0.90 - 0.15 seconds = 0.75 seconds
- 0.15 seconds
- 0.30 - 0.15 seconds = 0.15 seconds
- 0.15 seconds
The 291e also supports frequency modulation of each input which makes it possible to build both simple and complex FM operators. The fm circuit of the 291e is different than that of the 259e and 261e and less prone to aliasing. Combined with a 210e, the 291e supports the following FM algorithm constructs:
- M -> C This is the basic FM operator, where the ratio of M and C are simple integers, usually N:1, but can be whatever you choose. The 291e can provide three such operators.
- (M1 + M2) -> C A complex parallel FM operator (requires a 210e to sum the modulation signals). The 291e can provide three such operators.
- M1 -> M2 -> C A complex series of FM operators. This requires two 291e inputs.
- (M1 + M2) -> M3 -> C A more complex series of FM operators. This requires two 291e inputs.
- M1 -> (M2 + M3) -> C A more complex series of FM operators. This requires two 291e inputs.
- M1 -> M2 -> M3 -> C Requires all three 291e inputs. This basic algorithm has numerous variations as M1, M2, and M3 can each be summed (or not) with additional modulation inputs.
Thus a 291e can be a powerful FM workstation independent of its filtering abilities.
292e Quad Dynamics Manager
Bandpass filters are great for synthsizing formants, but two other filter types are also quite useful for creating "that sound" from a timbre: a low-pass filterLow-pass filter
A low-pass filter is an electronic filter that passes low-frequency signals but attenuates signals with frequencies higher than the cutoff frequency. The actual amount of attenuation for each frequency varies from filter to filter. It is sometimes called a high-cut filter, or treble cut filter...
and a high-pass filter
High-pass filter
A high-pass filter is a device that passes high frequencies and attenuates frequencies lower than its cutoff frequency. A high-pass filter is usually modeled as a linear time-invariant system...
. Consider the square wave
Square wave
A square wave is a kind of non-sinusoidal waveform, most typically encountered in electronics and signal processing. An ideal square wave alternates regularly and instantaneously between two levels...
which theoretically has an infinite number of only odd-order harmonics. If we want to "soften" the sound, we need to remove all the higher-order harmonics above whatever frequency we perceive as "harsh". For example, let's say that harmonics above 2.2 kHz are objectionable. For a square wave at A5, that's the 5th harmonic and above. For a square wave at A3, that's the 7th harmonic and above. For a square wave at A6, that's the 3rd harmonic and above. A low-pass filter can uniformly remove all offending high-frequency signals regardless of whether they are the 7th, 11th, or 13th harmonics, creating a greater consistency of tone than merely saying "let's just compose a wave consisting of the 1st, 3rd, and 5th harmonics", which gets it wrong for the higher registers.
The signal chain of the 292e Quad Dynamics Manager has a voltage-controlled low-pass filter that can operate in tandem with or instead of the VCA (aka gate). There appears to be no way to control the slope of the low-pass filter; it is fixed at 12db/octave. A popular enhancement to low-pass filters is resonance, which compensates (or overcompensates) for signal attenuation at the cutoff frequency. Since a resonant peak overlaid on a low-pass filter sounds a lot like a band-pass filter with some extra mojo, resonant low-pass filters have formant-forming qualities. The 292e does not support a resonance parameter, but the signal from a 292e can be added to a band-passed signal from a 291e to create a similar effect. FIXME: how do we tune the two different modules so that we know the resonant peak and the low pass filter are really in agreement? FIXME: is there some trick way to combine the two audio signals without burning a column of the 210e?
One way to achieve the effect of a high pass filter, other than possibly the warp control of the 259e and the timbre control of the 261e, is to mix together a lopass filtered signal with the original signal, with one of them inverted in polarity. On the 200e, the only proven phase inverter is the submixer of the 227e, and then only the signal added via the "In The Mix" switch is inverted. There is no evidence that the 210e nor the accessible submixer outputs of the 227e are inverting.
4-pole LPF using 292e
I'm guessing that the 292e implements a 2-pole (aka second-order) LPF, but what if one wants a 4-pole LPF? Simple, just allocate 2 292e circuits, feed them with identical CV inputs, apply identical knob settings, feed the signal to be filtered into the first, the output of the first to the input of the second, and the output of the first will be a 4-pole LPF.If I'm wrong and the 292e just implements a first-order filter, the above will give the effect of a second-order filter and all four units will need to be connected to implement a fourth-order filter.
Portamento using the 266e and 256e
Here is a method I've discovered to jury rigJury rig
Jury rigging refers to makeshift repairs or temporary contrivances, made with only the tools and materials that happen to be on hand. Originally a nautical term, on sailing ships a jury rig is a replacement mast and yards improvised in case of damage or loss of the original mast.-Etymology:The...
a portamento effect by using the 266e Source of Uncertainty in a certain way. The basic idea is simple: since portamento is a glide between one pitch and another, we need a way to capture a pitch so that when a new pitch is played we can glide from the original pitch to the new target pitch. We do this by configuring the Stored Random Voltages section of the 266e as a Sample-and-Hold function: set "skew" to the leftmost position and connect the voltage to be sampled to the CV input for "skew". Set "degree" and "chaos" to zero. The output of the Sample-and-Hold function is our original note (sort of) and the current MIDI pitch (as a control voltage) is the target pitch. To glide from one to the other, we put the two pitch voltages into the two source inputs of a 256e Control Voltage Processor circuit and use the output of a 281e Quad Function Generator to pan from the original pitch to the new pitch. The Attack parameter of the 281e defines the glide speed.
The pulse network is a bit tricky: the MIDI note on pulse triggers the 281e envelope, which is configured in transient mode. The output of the 281e drives not only the selection logic of the 256e, but also a second circuit in the 256e. This second circuit is configured to generate a pulse at the end of the attack phase by using a breakpoint function (in value = 8 V, out value = 0 V). The output of this second circuit drives the "update" input of the 266e. The 281e produces a pulse at the end of the decay phase of the envelope, but that is too late: we need to sample the pitch before the decay, else our selection logic will drop back to the initial pitch and we'll hear a glitch. By sampling the pitch just as we reach the top, there won't be a glitch when the 281e envelope decays and the first 256e circuit switches back from MIDI pitch to sampled pitch.
Would that it were so simple! For reasons I do not yet understand, the 266e flattens out voltages, which has the effect of changing an octave scale into something not quite an octave. If it stretched pitch instead of shrinking it we could fix the problem with a single 256e circuit. This is because we could raise the Output @ 0 V, lower the Output @ 10 V, creating a transfer function of something like 0.8:1 and the product of the two would be a nice 1:1 transfer function. Since the incoming scale is flattened, we need a transfer function that's more like 1.25:1, and that requires two 256e circuits. The first circuit uses a breakpoint function to produce 10 V at approx 8 V input. The second circuit uses a breakpoint function to produce 0 V at approx 2 V input. By running these in series we get our (> 1):1 transfer function, and pitch is restored (to within perhaps 20 cents, because all these pitch transformations add up their pitch errors). The output of the corrected sample pitch is the actual input we use for the 256e selection circuit, not the output of the 266e directly.
Of course we can also use this portamento method to drive the frequency of a 291e or 292e filter to get the classic ELP
Emerson, Lake & Palmer
Emerson, Lake & Palmer, also known as ELP, are an English progressive rock supergroup. They found success in the 1970s and sold over forty million albums and headlined large stadium concerts. The band consists of Keith Emerson , Greg Lake and Carl Palmer...
effect of a glide opening up with a big "BWAHH!" at the finish.
n.b. It is also possible to save two 256e circuits by doing the following. By using two separate pitch busses on the 225e unit we can tune the offset of each separately. Let's call the first bus the Hold bus (used to feed the 266e Sample-and-Hold circuit) and the second bus the Now bus (the pitch currently being played). By using a 210e CV circuit, we can flatten the pitch of the Now bus so it has exactly the same slope as the output of the 266e (which is fed by, but is not itself, the Hold bus). Tuning the offsets of the two pitches helps set the slope correctly across a range of notes. Now that both inputs to the poramento selector circuit behave the same for a given pitch, we can correct the flat slop by using a breakpoint function. By setting the breakpoint out value to zero and setting the in value to around 2 V, we create a slope that is greater than unity, offsetting the less-than-unity slop of the 266e and the intentionally less-than-unity 210e output. We tune the 256e circuit until the slope of the breakpoint function cancels out the slopes of the input functions and now we can feed the CV output to the CV input of an oscillator like the 261e, tune it to 1.2 V/octave and we're good to go. It's a good idea to conserve 256e circuits because they can be useful for other things...
Constant Rate Portamento
The previous method gives a constant time portamento: whether the pitch difference is one semitone or 48, it takes the same amount of time to g-l-i-d-e up or down to the next pitch. A constant rate portamento moves some number of semitones per second, meaning that the portamento between notes close together will be almost imperceptible, whereas notes several octaves apart will give a very strong portamento effect. To do this we need to calculate the difference between two pitches and use that as a factor of how quickly the Attack parameter of the 281e envelope changes the selection between the original note (which we'll call P1) and the target note (P2).To calculate the difference between two notes we need two circuits of the 256e and a summing circuit from the 210e. The first 256e circuit is configured as a negative transfer function giving us 10 V - P1 for an input of P1. We use the 210e to add (10 V - P1) /2 with P2/2, giving 5 V + (P2 - P1) /2 and feed this output to the input of the second 256e circuit. The second 256e circuit is configured as a non-linear transfer function that looks like the letter V. I.e., it gives 10 V - 2*Vin when Vin <= 5 V and 2*Vin - 10 when Vin > 5 V. When P1 is near P2, then 5 V + P2 - P1 is near 5 V and the non-linear transformation gives us a value near 0 V, a very short time for the portamento glide time. When P1 is two octaves (2.4 V) less than P2, then 5 V + P2 - P1 is 7.4 V and the non-linear transformation gives us 14.8 V - 10 V or 4.8 V, a good amount of glide time. Similarly when P1 is two octaves above P2 (2.4 V), then 5 V + P2 - P1 is 2.6 V and the non-linear transformation gives us 10 V - 5.2 V = 4.8 V, an equally good amount of glide time. In either case, the 4.8 V can be multiplied by the attack time of the 281e unit to get the right amount of portamento time.
This setup uses 3 210e inputs, 4 256e circuits, 1 266e input in the Stored Random Voltages section, 1 281e envelope generator circuit, and 2-3 MIDI pitch outputs of a 225e circuit, not including the number of oscillators, evelope generators, filters, and VCAs needed to generate a sound.
Extra-Low LFO using the 281e
When the input mode is set to periodic, the 281e Quad Function Generators can function as Low Frequency Oscillator with a frequency ranging from 1/20th Hz (producing a triangle wave) to 1/10 Hz (becoming a rising or falling sawtooth wave), to any type of wave in between triangle and sawtooth up to 500 Hz.Clock Multiplier Using the 256e
Doubling the frequency of a triangle wave LFO signal is possible using one channel of the 256e. Use a breakpoint in the 256e channel to set a maximum peak in the center, and set both endpoints to zero. An LFO triangle wave input will result in a triangle wave output at double the frequency. The source LFO triangle can be created using one channel of a 281e, with attack and decay knobs set to roughly the same position.285e Balanced Modulator as Sound Source
Feeding the outputs of the 285e Balanced Modulator back into its signal inputs turns the module into a pair of VCOs. On the ring mod side (the bottom half) route one of the "voltage controlled" outputs to the signal input. Monitor the voltage controlled output (on its multed jack). Adjust the modulation knob and frequency knob to about 3 o'clock. The frequency cv input will now alter the pitch. The signal will go smoothly to LFO rates. On the frequency shifter side (top half) mix the up and down outputs using a 210e. Monitor this signal and also feed it back to the signal input. Adjust the frequency knob to about 3 o'clock. Again, the frequency cv will alter the pitch. It is also possible to use the balanced modulator side as a sound source for the frequency shifting side and vice-versa. Many cross modulation possibilities exist (use of the 210e is optional), and typically yield interesting results.Tips and hidden features
- You can enable or disable the Remote Enables of all modules in a system with the Preset Manager section of the 225e. Use the DATA switch to select "global". The top line of first global page reads Remote Status. The DATA knob will now enable and disable remote all the modules in a system.
- You can recalibrate the 259e by removing all patch cords, setting all knobs to full CCW, and holding down the sync button while cycling power.
Gotchas
The "Remote Enable" switch has a dual meaning on several modules.- 259e and 261e: causes the principal oscillator to track midi notes. This can lead to surprising results when you've configured your oscillator to run off a CV pitch and use Remote Enable just to restore other parameters of the module.
- 281e: causes the envelopes to open for MIDI note on events. Again, this can lead to surprising results when you just want to restore envelope attack types (continuous, transient, or sustain) or quadrature mode.
- 292e: causes the "VCA"s to react to Velocity.