Quasi-peak

Quasi-peak

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 rectifiers. 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 cite web |url=http://www.ieee.org/organizations/pubs/newsletters/emcs/summer01/pp.bronaugh.htm |title=The Quasi-Peak Detector |author=Edwin L. Bronaugh |year=2001 |accessdate=2007-09-07] . Over time standards incorporating quasi-peak detectors as the measurement device were extended to frequencies up to 1 GHz cite web |url=http://www.dbicorporation.com/ite.htm |title= EMC/EMI/ESD STANDARDS FOR INFORMATION TECHNOLOGY EQUIPMENT (ITE) |author=John R. Barnes |date=2003-07-23 |accessdate=2007-09-07] , 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 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 [cite web
title = American National Standard for Electromagnetic Noise and Field Strength Instrumentation, 10 Hz to 40 GHz-Specifications
work = ANSI C63.2-1996
publisher = IEEE
date = 1996-01-12
url = http://standards.ieee.org/reading/ieee/std_public/description/emc/C63.2-1996_desc.html
accessdate = 2007-09-07
] .

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 constants. 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.

See also

*Measuring receiver

References


Wikimedia Foundation. 2010.

Игры ⚽ Нужна курсовая?

Look at other dictionaries:

  • Peak programme meter — A typical British quasi PPM. Each division between 1 and 7 is exactly four decibels and 6 is the intended maximum level. A peak programme meter (PPM) is an instrument used in professional audio for indicating the level of an audio signal. There… …   Wikipedia

  • Peak Program Meter — Ein Aussteuerungsmesser (auch: Pegelmesser) ist ein Anzeigeinstrument zur Kontrolle der Aussteuerung bei Tonaufnahmen. Inhaltsverzeichnis 1 Technische Eigenschaften 1.1 Bauarten 1.1.1 Spitzenpegelmesser 1.1.2 Gleichrichtwert Pegelmesser …   Deutsch Wikipedia

  • Peak Programme Meter — Ein Aussteuerungsmesser (auch: Pegelmesser) ist ein Anzeigeinstrument zur Kontrolle der Aussteuerung bei Tonaufnahmen. Inhaltsverzeichnis 1 Technische Eigenschaften 1.1 Bauarten 1.1.1 Spitzenpegelmesser 1.1.2 Gleichrichtwert Pegelmesser …   Deutsch Wikipedia

  • Peak meter — A peak meter is a type of visual measuring instrument that indicates the instantaneous level of an audio signal that is passing through it (a sound level meter). In sound reproduction, the meter, whether peak or not, is usually meant to… …   Wikipedia

  • Peak Programme Meter — PPM, échelle audio numérique (IEC 268 18). Un peak programme meter (PPM) est un Instrument de mesure utilisé par les professionnels du son pour indiquer le niveau d un signal audio. Sommaire 1 …   Wikipédia en Français

  • Quasi-periodic oscillations — In high energy (X ray) astronomy, quasi periodic oscillations (QPOs) refer to the way the X ray light from an astronomical object flickers about certain frequencies. In these situations, the X rays are emitted near the inner edge of an accretion… …   Wikipedia

  • Lichtzeigerinstrument — Ein Aussteuerungsmesser (auch: Pegelmesser) ist ein Anzeigeinstrument zur Kontrolle der Aussteuerung bei Tonaufnahmen. Inhaltsverzeichnis 1 Technische Eigenschaften 1.1 Bauarten 1.1.1 Spitzenpegelmesser 1.1.2 Gleichrichtwert Pegelmesser …   Deutsch Wikipedia

  • Peakmeter — Ein Aussteuerungsmesser (auch: Pegelmesser) ist ein Anzeigeinstrument zur Kontrolle der Aussteuerung bei Tonaufnahmen. Inhaltsverzeichnis 1 Technische Eigenschaften 1.1 Bauarten 1.1.1 Spitzenpegelmesser 1.1.2 Gleichrichtwert Pegelmesser …   Deutsch Wikipedia

  • Pegelmesser — Ein Aussteuerungsmesser (auch: Pegelmesser) ist ein Anzeigeinstrument zur Kontrolle der Aussteuerung bei Tonaufnahmen. Inhaltsverzeichnis 1 Technische Eigenschaften 1.1 Bauarten 1.1.1 Spitzenpegelmesser 1.1.2 Gleichrichtwert Pegelmesser …   Deutsch Wikipedia

  • Spitzenwertmesser — Ein Aussteuerungsmesser (auch: Pegelmesser) ist ein Anzeigeinstrument zur Kontrolle der Aussteuerung bei Tonaufnahmen. Inhaltsverzeichnis 1 Technische Eigenschaften 1.1 Bauarten 1.1.1 Spitzenpegelmesser 1.1.2 Gleichrichtwert Pegelmesser …   Deutsch Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”