Peak Program Meter (PPM)
A Peak Program Monitor (PPM), sometimes referred to as a Peak Reading Meter (PRM), is an audio metering device. It's general function is similar to a VU meter but there are some important differences.
The rise time of a PPM (the time it takes to register the level of a sound) is much faster than a VU meter, typically 10 milliseconds compared to 300 milliseconds. This makes transient peaks easier to measure.
The fall time of a PPM (the time it takes the meter to return to a lower reading) is much slower.
PPM meters are very good for reading fast, transient sounds. This is especially useful in situations where pops and distortion are a problem.
See also: VU (volume unit) Meter