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.
In professional usage, where consistent level measurements are needed across an industry, audio level meters often comply with a detailed formal standard. This ensures that all meters that comply with the standard will give the same indication on a given audio signal. The principal standard for PPMs is IEC 60268-10. It describes two different quasi-PPM designs which have their roots in meters originally developed in the 1930s for the AM radio broadcasting networks of Germany (Type I) and the United Kingdom (Type II).
The term Peak Programme Meter usually refers to these IEC-specified types and similar designs.
PPMs were originally designed for monitoring analogue audio signals but are now also used with digital audio.
PPMs do not provide effective loudness monitoring. Newer types of meter do, and there is now a push within the broadcasting industry to move away from traditional level meters such as those featured in this article to two new types: loudness meters based on EBU Tech. 3341 and oversampling true PPMs. The former would be used to standardise broadcast loudness to −23 LUFS and the latter to prevent digital clipping.
Read more about Peak Programme Meter: History and National Variants, Nagra Modulometer, Usage of Meter By Sound Balancers, PPMs and Digital Audio Levels, PPMs For Consumer Use
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