Many operators prefer the moving-coil meter type of display, in which a needle moves in an arc, because they feel the angular movement is easier for the human eye to monitor than the linear movement of a bar graph. For these, IEC 60268-10 requires a minimum of 100 segments and a resolution better than 0.5 dB at the higher levels. Nowadays PPMs are often implemented as 'bargraph' incremental displays using solid-state illuminated segments in a vertical or horizontal array. These displays require active driver electronics. These took the form of moving-coil panel meters or mirror galvanometers with demanding 'ballistics': the key requirement being that the indicated level should rise as quickly as possible with negligible overshoot. In common with many other types of audio level meter, PPMs originally used electro-mechanical displays. PPMs need active driver electronics – shown here mounted on back of meter movement Display technologies The former would be used to standardise broadcast loudness to −23 LUFS and the latter to prevent digital clipping. Newer types of meter do, and there is now a push within the broadcasting industry to move away from the traditional level meters in this article to two new types: loudness meters based on EBU Tech.
PPMs do not provide effective loudness monitoring. Though originally designed for monitoring analogue audio signals, these PPMs are now also used with digital audio. The term Peak Programme Meter usually refers to these IEC-specified types and similar designs. It describes two different quasi-PPM designs that have 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 principal standard for PPMs is IEC 60268-10. This ensures that all compliant meters indicate the same level for a given audio signal. In professional use, which requires consistent level measurements across an industry, audio level meters often comply with a formal standard. This is a sample PPM that first oversamples the signal, typically by a factor of four, to alleviate the problems of a basic sample PPM. It may have either a 'true' or a 'quasi' integration characteristic. It shows only peak sample values, not true waveform peaks (which may fall between samples and be up to 3 dB higher in amplitude). The extent of the shortfall is determined by the 'integration time'. On peaks of shorter duration, it indicates less than the true peak level.
This only shows the true level of the peak if it exceeds a certain duration, typically a few milliseconds. This shows the peak level of the waveform no matter how brief its duration. Each division between '1' and '7' is exactly four decibels and '6' is the intended maximum level.Ī peak programme meter ( PPM) is an instrument used in professional audio that indicates the level of an audio signal.ĭifferent kinds of PPM fall into broad categories: