Peak programme meter

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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 are many different kinds of PPM. They fall into broad categories:

True peak programme meter. This shows the peak level of the waveform no matter how brief its duration.
Quasi peak programme meter (QPPM). This only shows the true level of the peak if it exceeds a certain duration, typically a few milliseconds. On peaks of shorter duration, it will indicate less than the true peak level. The extent of the shortfall is determined by the 'integration time'.
Sample peak programme meter (SPPM). This is a PPM for digital audio which shows only peak sample values, not the true waveform peaks (which may fall between samples and be up to 3 dB higher in amplitude). It may have either a 'true' or a 'quasi' integration characteristic.
Over-sampling peak programme meter. This is a sample PPM in which the signal has first been over-sampled, typically by a factor of four, to alleviate the problem with a basic sample PPM.

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Posted by: bigfish@pacbell.net

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