Quasi-peak
Encyclopedia
Quasi-peak means 'not quite peak', or 'aiming towards peak but not actually peak'. The term is commonly used when referring to electronic detectors or rectifier
s. Despite the above definition, the term quasi-peak should not be interpreted as vague in any way. Quasi-peak detectors for specific purposes usually have been standardized with mathematically precisely defined dynamic characteristics, in terms of 'attack time', 'integration time', and 'decay time' or 'fall-back' time.
Quasi-peak detectors play an important role in electromagnetic compatibility
(EMC) testing of electronic equipment, where allowed levels of electromagnetic interference
(EMI), also called radio frequency interference (RFI), are given with reference to measurement by a specified quasi-peak detector. This was originally done because the quasi-peak detector was believed to better indicate the subjective annoyance level experienced by a listener hearing impulsive interference to an AM
radio station . Over time standards incorporating quasi-peak detectors as the measurement device were extended to frequencies up to 1 GHz
, although there may not be any justification beyond previous practice for using the quasi-peak detector to measure interference to signals other than AM
radio . The CISPR does not currently limit EMI
at frequencies above 1 GHz
, and the U.S. Federal Communications Commission
(FCC) specifies allowed EMI
above 1 GHz
with reference to an average-power detector . The quasi-peak detector parameters to be used for EMC
testing vary with frequency
.
Conceptually, a quasi-peak detector for EMC
testing works like a peak detector followed by a lossy integrator.
A voltage impulse entering a narrow-band receiver produces a short-duration burst oscillating at the receiver center frequency. The peak detector is a rectifier followed by a low-pass filter
to extract a baseband signal consisting of the slowly (relative to the receiver center frequency) time-varying amplitude of the impulsive oscillation. The following lossy integrator has a rapid rise time and longer fall time, so the measured output for a sequence of impulses is higher when the pulse repetition rate is higher. The quasi-peak detector is calibrated to produce the same output level as an average-power detector when the input is a continuous wave
tone in the receiver bandwidth.
In audio quality measurement
, quasi-peak rectifiers are specified in several standards. For example ITU-R 468 noise weighting
uses a special rectifier incorporating two cascaded charging time constant
s. The PPM or peak programme meter
used to measure programme levels is actually a quasi-peak reading meter, again with precisely defined dynamics. Flutter measurement also involves a standardised quasi-peak reading meter. In every case the dynamics are chosen to reflect the sensitivity of human hearing to brief sounds, ignoring those so brief that we do not perceive them, and weighting
those of intermediate duration according to audibility.
Rectifier
A rectifier is an electrical device that converts alternating current , which periodically reverses direction, to direct current , which flows in only one direction. The process is known as rectification...
s. Despite the above definition, the term quasi-peak should not be interpreted as vague in any way. Quasi-peak detectors for specific purposes usually have been standardized with mathematically precisely defined dynamic characteristics, in terms of 'attack time', 'integration time', and 'decay time' or 'fall-back' time.
Quasi-peak detectors play an important role in electromagnetic compatibility
Electromagnetic compatibility
Electromagnetic compatibility is the branch of electrical sciences which studies the unintentional generation, propagation and reception of electromagnetic energy with reference to the unwanted effects that such energy may induce...
(EMC) testing of electronic equipment, where allowed levels of electromagnetic interference
Electromagnetic interference
Electromagnetic interference is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit...
(EMI), also called radio frequency interference (RFI), are given with reference to measurement by a specified quasi-peak detector. This was originally done because the quasi-peak detector was believed to better indicate the subjective annoyance level experienced by a listener hearing impulsive interference to an AM
Amplitude modulation
Amplitude modulation is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent...
radio station . Over time standards incorporating quasi-peak detectors as the measurement device were extended to frequencies up to 1 GHz
GHZ
GHZ or GHz may refer to:# Gigahertz .# Greenberger-Horne-Zeilinger state — a quantum entanglement of three particles.# Galactic Habitable Zone — the region of a galaxy that is favorable to the formation of life....
, although there may not be any justification beyond previous practice for using the quasi-peak detector to measure interference to signals other than AM
Amplitude modulation
Amplitude modulation is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent...
radio . The CISPR does not currently limit EMI
Electromagnetic interference
Electromagnetic interference is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit...
at frequencies above 1 GHz
GHZ
GHZ or GHz may refer to:# Gigahertz .# Greenberger-Horne-Zeilinger state — a quantum entanglement of three particles.# Galactic Habitable Zone — the region of a galaxy that is favorable to the formation of life....
, and the U.S. Federal Communications Commission
Federal Communications Commission
The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...
(FCC) specifies allowed EMI
Electromagnetic interference
Electromagnetic interference is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit...
above 1 GHz
GHZ
GHZ or GHz may refer to:# Gigahertz .# Greenberger-Horne-Zeilinger state — a quantum entanglement of three particles.# Galactic Habitable Zone — the region of a galaxy that is favorable to the formation of life....
with reference to an average-power detector . The quasi-peak detector parameters to be used for EMC
Electromagnetic compatibility
Electromagnetic compatibility is the branch of electrical sciences which studies the unintentional generation, propagation and reception of electromagnetic energy with reference to the unwanted effects that such energy may induce...
testing vary with frequency
.
Conceptually, a quasi-peak detector for EMC
Electromagnetic compatibility
Electromagnetic compatibility is the branch of electrical sciences which studies the unintentional generation, propagation and reception of electromagnetic energy with reference to the unwanted effects that such energy may induce...
testing works like a peak detector followed by a lossy integrator.
A voltage impulse entering a narrow-band receiver produces a short-duration burst oscillating at the receiver center frequency. The peak detector is a rectifier followed by a low-pass filter
Low-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...
to extract a baseband signal consisting of the slowly (relative to the receiver center frequency) time-varying amplitude of the impulsive oscillation. The following lossy integrator has a rapid rise time and longer fall time, so the measured output for a sequence of impulses is higher when the pulse repetition rate is higher. The quasi-peak detector is calibrated to produce the same output level as an average-power detector when the input is a continuous wave
Continuous wave
A continuous wave or continuous waveform is an electromagnetic wave of constant amplitude and frequency; and in mathematical analysis, of infinite duration. Continuous wave is also the name given to an early method of radio transmission, in which a carrier wave is switched on and off...
tone in the receiver bandwidth.
In audio quality measurement
Audio quality measurement
Audio quality measurement seeks to quantify the various forms of corruption present in an audio system or device. The results of such measurement are used to maintain standards in broadcasting, to compile specifications, and to compare pieces of equipment....
, quasi-peak rectifiers are specified in several standards. For example ITU-R 468 noise weighting
ITU-R 468 noise weighting
ITU-R 468 is a standard relating to noise measurement, widely used when measuring noise in audio systems. The standard defines a weighting filter curve, together with a quasi-peak rectifier having special characteristics as defined by specified tone-burst tests...
uses a special rectifier incorporating two cascaded charging time constant
Time constant
In physics and engineering, the time constant, usually denoted by the Greek letter \tau , is the risetime characterizing the response to a time-varying input of a first-order, linear time-invariant system.Concretely, a first-order LTI system is a system that can be modeled by a single first order...
s. The PPM or peak programme meter
Peak programme meter
A peak programme meter is an instrument used in professional audio for indicating the level of an audio signal.There are many different kinds of PPM. They fall into broad categories:...
used to measure programme levels is actually a quasi-peak reading meter, again with precisely defined dynamics. Flutter measurement also involves a standardised quasi-peak reading meter. In every case the dynamics are chosen to reflect the sensitivity of human hearing to brief sounds, ignoring those so brief that we do not perceive them, and weighting
Weighting
The process of weighting involves emphasizing the contribution of some aspects of a phenomenon to a final effect or result — giving them 'more weight' in the analysis. That is, rather than each variable in the data contributing equally to the final result, some data are adjusted to contribute...
those of intermediate duration according to audibility.