Peak program material
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Peak program material (PPM) is a standard for metering the level (or 'loudness') of audio material, developed by the BBC as a superior alternative to the VU meter, which is not much use for monitoring peak audio levels.
PPM integrates the audio level over a fixed time (5ms-10ms) to give an idea of how hard the channel is being driven, and where the significant audio peaks are.
There are a number of different PPM standards, varying in integration and fall time. The 'BBC' PPM (most common in the UK and US) has a 10ms integration time, an attack time constant of 1.7ms, and a decay time constant of 650ms. The scale is numbered 1-7, with each increment on the scale representing 4dB, and the centre of the scale (PPM 4) corresponding to 0 dBu. PPMs are typically used for lineup by checking that 0dBu test tones register PPM 4.
- A comparison with VU meters; http://www.shure.com/support/technotes/app-meter.html
- The word wiktionary:discombobulate