Sample-based synthesis
Encyclopedia
Sample-based synthesis is a form of audio synthesis that can be contrasted to either subtractive synthesis
or additive synthesis
. The principal difference with sample-based synthesis is that the seed waveforms are sampled sounds or instruments instead of fundamental waveforms such as the saw waves of subtractive synthesis or the sine waves
of additive synthesis.
or additive synthesis is that processing power requirements are much lower. This is because most of the nuances of the sound models are contained in the pre-recorded samples rather than calculated in real-time.
In a contrast to analog synthesizers, the circuitry does not have to be duplicated to allow more voices to be played at once. Therefore the polyphony
of sample-based machines is generally a lot higher. A downside is, however, that in order to include more detail, multiple samples might need to be played back at once (a trumpet might include a breath noise, a growl, and a looping soundwave used for continuous play). This reduces the polyphony again, as sample-based synthesizers rate their polyphony based on the number of multi-samples that can be played back simultaneously.
As memory became cheaper, it became possible to use multisampling; instead of a single recording of an instrument being played back faster or slower to reproduce other pitches, the original instrument could be sampled at regular intervals to cover regions of several adjacent notes (called "splits") or for every note. This provides a more natural progression from the lower to the higher registers; lower notes don't sound dull, and higher notes don't sound unnaturally bright. It is also possible to sample the same note at several different levels of intensity, reflecting the fact that both volume and timbre change with playing style. For instance, when sampling a piano, 3 samples per key can be made; soft, medium and with force. Every possible volume in between can be made by amplifying and blending the samples.
For sample-based models of instruments like the Rhodes piano
, this multisampling is very important. The timbre of the Rhodes changes drastically from left to right on the keyboard, and it varies greatly depending on the force with which the key is struck. The lower registers "bark", while the higher range has a more bell-like sound. The bark will be more distinct if the keys are struck with force. For the model to be sufficiently expressive, it is therefore necessary that multisamples be made across both pitch and force of playing.
(1960s) used analog tape decks to play back sampled sounds.
When sample-based synthesis was first developed, most affordable consumer synthesizers could not record arbitrary samples, but instead formed timbres by combining pre-recorded samples from ROM
before routing the result through analog or digital
filters
. These synthesizers and their more complex descendants are often referred to as ROMplers.
Sample-based instruments have been used since the Computer Music Melodian, the CMI Fairlight and the NED Synclavier. These instruments were way ahead of their time and were correspondingly expensive. The first recording using a sampling synthesizer was Stevie Wonder's "Secret Life of Plants" (1976) which used the Melodian to create complex melodies and rhythms from sampled sounds from nature. The first tune Wonder recorded was "The First Garden" where he used a sampled bird chirp as the lead sound in the song. More affordable sample-based synthesizers available for the masses with the introduction of the Roland D-50
and the Korg M1
, which surfaced in the late eighties. The M1 also introduced the "workstation" concept.
The concept has made it into hi-end sound cards for the Multimedia PC
, under the (incorrect) name of 'wavetable synthesis
'.
. Early samplers were very expensive, and typically had low sample rates and bit depth
, resulting in grainy and aliased
sound. Since the mid 1990s, however, samplers have featured specifications at least as good as CD
s. By the late 1990s, the huge increases in computer processor speed permitted the widespread development of software synthesizer
s and software sampler
s. The vast storage capacity of modern computers was ideally suited to sample-based synthesis, and many samplers have thus migrated to software implementations or been superseded by new software samplers.
Subtractive synthesis
Subtractive synthesis is a method of sound synthesis in which partials of an audio signal are attenuated by a filter to alter the timbre of the sound...
or additive synthesis
Additive synthesis
Additive synthesis is a technique of sound synthesis that creates musical timbre by explicitly adding sinusoidal overtones together.The timbre of an instrument is composed of multiple harmonic or inharmonic partials , of different frequencies and amplitudes, that change over time...
. The principal difference with sample-based synthesis is that the seed waveforms are sampled sounds or instruments instead of fundamental waveforms such as the saw waves of subtractive synthesis or the sine waves
Sine
In mathematics, the sine function is a function of an angle. In a right triangle, sine gives the ratio of the length of the side opposite to an angle to the length of the hypotenuse.Sine is usually listed first amongst the trigonometric functions....
of additive synthesis.
Advantages of sample-based synthesis
Sample-based synthesis' principal advantage over other methods of digital synthesis such as physical modelling synthesisPhysical modelling synthesis
In sound synthesis, physical modelling synthesis refers to methods in which the waveform of the sound to be generated is computed by using a mathematical model, being a set of equations and algorithms to simulate a physical source of sound, usually a musical instrument...
or additive synthesis is that processing power requirements are much lower. This is because most of the nuances of the sound models are contained in the pre-recorded samples rather than calculated in real-time.
In a contrast to analog synthesizers, the circuitry does not have to be duplicated to allow more voices to be played at once. Therefore the polyphony
Polyphony
In music, polyphony is a texture consisting of two or more independent melodic voices, as opposed to music with just one voice or music with one dominant melodic voice accompanied by chords ....
of sample-based machines is generally a lot higher. A downside is, however, that in order to include more detail, multiple samples might need to be played back at once (a trumpet might include a breath noise, a growl, and a looping soundwave used for continuous play). This reduces the polyphony again, as sample-based synthesizers rate their polyphony based on the number of multi-samples that can be played back simultaneously.
Multisampling
A sample-based synthesizer's ability to reproduce the nuances of natural instruments is determined primarily by its library of sampled sounds. In the earlier days of sample-based synthesis, computer memory was expensive and samples had to be as short and as few as possible. This was achieved by looping a part of the sample (often a single wave), and then using a volume envelope curve to make the sound fade away. An amplifying stage would translate key velocity into gain so that harder playing would translate into louder playback. In some cases key velocity also modulates the attack time of the instrument, leading to a faster attack for loud passages.As memory became cheaper, it became possible to use multisampling; instead of a single recording of an instrument being played back faster or slower to reproduce other pitches, the original instrument could be sampled at regular intervals to cover regions of several adjacent notes (called "splits") or for every note. This provides a more natural progression from the lower to the higher registers; lower notes don't sound dull, and higher notes don't sound unnaturally bright. It is also possible to sample the same note at several different levels of intensity, reflecting the fact that both volume and timbre change with playing style. For instance, when sampling a piano, 3 samples per key can be made; soft, medium and with force. Every possible volume in between can be made by amplifying and blending the samples.
For sample-based models of instruments like the Rhodes piano
Rhodes piano
The Rhodes piano is an electro-mechanical piano, invented by Harold Rhodes during the fifties and later manufactured in a number of models, first in collaboration with Fender and after 1965 by CBS....
, this multisampling is very important. The timbre of the Rhodes changes drastically from left to right on the keyboard, and it varies greatly depending on the force with which the key is struck. The lower registers "bark", while the higher range has a more bell-like sound. The bark will be more distinct if the keys are struck with force. For the model to be sufficiently expressive, it is therefore necessary that multisamples be made across both pitch and force of playing.
History
Before digital recording became practical, instruments such as the phonogene (1950s) and the MellotronMellotron
The Mellotron is an electro-mechanical, polyphonic tape replay keyboard originally developed and built in Birmingham, England in the early 1960s. It superseded the Chamberlin Music Master, which was the world's first sample-playback keyboard intended for music...
(1960s) used analog tape decks to play back sampled sounds.
When sample-based synthesis was first developed, most affordable consumer synthesizers could not record arbitrary samples, but instead formed timbres by combining pre-recorded samples from ROM
Read-only memory
Read-only memory is a class of storage medium used in computers and other electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly or with difficulty, so it is mainly used to distribute firmware .In its strictest sense, ROM refers only...
before routing the result through analog or digital
Digital
A digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...
filters
Electronic filter
Electronic filters are electronic circuits which perform signal processing functions, specifically to remove unwanted frequency components from the signal, to enhance wanted ones, or both...
. These synthesizers and their more complex descendants are often referred to as ROMplers.
Sample-based instruments have been used since the Computer Music Melodian, the CMI Fairlight and the NED Synclavier. These instruments were way ahead of their time and were correspondingly expensive. The first recording using a sampling synthesizer was Stevie Wonder's "Secret Life of Plants" (1976) which used the Melodian to create complex melodies and rhythms from sampled sounds from nature. The first tune Wonder recorded was "The First Garden" where he used a sampled bird chirp as the lead sound in the song. More affordable sample-based synthesizers available for the masses with the introduction of the Roland D-50
Roland D-50
The Roland D-50 is a polyphonic 61-key synthesizer produced by Roland. It was released in 1987. Its features include Linear Arithmetic synthesis, on-board effects, a joystick for data manipulation, and an analog synthesis-styled layout design. The external Roland PG-1000 Programmer could also be...
and the Korg M1
Korg M1
The Korg M1 is the world's first widely-known music workstation. Its onboard MIDI sequencer and palette of sounds allowed musicians to produce complete professional arrangements...
, which surfaced in the late eighties. The M1 also introduced the "workstation" concept.
The concept has made it into hi-end sound cards for the Multimedia PC
Multimedia PC
The Multimedia PC, or MPC, was a recommended configuration for a PC with a CD-ROM drive. The standard was set and named by the "Multimedia PC Marketing Council", which was a working group of the Software Publishers Association . The MPMC comprised companies including Microsoft, Creative Labs,...
, under the (incorrect) name of 'wavetable synthesis
Wavetable synthesis
Wavetable synthesis is used in certain digital music synthesizers to implement a restricted form of real-time additive synthesis. The technique was first developed by Wolfgang Palm of PPG in the late 1970s and published in 1979, and has since been used as the primary synthesis method in...
'.
Sampling synthesizers
A more flexible sample-based synthesis design allowing the user to record arbitrary waveforms to form a sound's basic timbre is called a samplerSampler (musical instrument)
A sampler is an electronic musical instrument similar in some respects to a synthesizer but, instead of generating sounds, it uses recordings of sounds that are loaded or recorded into it by the user and then played back by means of a keyboard, sequencer or other triggering device to perform or...
. Early samplers were very expensive, and typically had low sample rates and bit depth
Bit depth
Bit depth may refer to:* For bit depth in graphics, see color depth* For bit depth in audio, see audio bit depth* For bit depth in drilling for petroleum, see drilling rig...
, resulting in grainy and aliased
Aliasing
In signal processing and related disciplines, aliasing refers to an effect that causes different signals to become indistinguishable when sampled...
sound. Since the mid 1990s, however, samplers have featured specifications at least as good as CD
Compact Disc
The Compact Disc is an optical disc used to store digital data. It was originally developed to store and playback sound recordings exclusively, but later expanded to encompass data storage , write-once audio and data storage , rewritable media , Video Compact Discs , Super Video Compact Discs ,...
s. By the late 1990s, the huge increases in computer processor speed permitted the widespread development of software synthesizer
Software synthesizer
A software synthesizer, also known as a softsynth is a computer program or plug-in for digital audio generation. Computer software which can create sounds or music is not new, but advances in processing speed are allowing softsynths to accomplish the same tasks that previously required dedicated...
s and software sampler
Software sampler
A software sampler is a piece of software which allows a computer to emulate the functionality of a sampler.In the same way that a sampler has much in common with a synthesizer, software samplers are in many ways similar to software synthesizers and there is great deal of overlap between the two,...
s. The vast storage capacity of modern computers was ideally suited to sample-based synthesis, and many samplers have thus migrated to software implementations or been superseded by new software samplers.