ABSTRACT
Some amplifiers and the more sophisticated mixers are fitted with a ‘signal-present’ indicator that illuminates to give reassurance that a channel is receiving a signal and doing something with it. A mixer has a relatively complex signal path, and the main metering is normally connected only to the group outputs. The mix metering can be used to measure the level in other parts of the signal path by use of the PFL system if fitted, but this can only monitor one channel at a time. One apparently ingenious way to gain a few more square millimetres of panel space is to combine the Signal-present and peak indicators into one by using a bi-colour LED. Peak programme meters (PPMs) are essentially peak-reading instruments that respond much more quickly than VU meters. The PPM standard was originally developed by the BBC in 1938 as a response to the inadequacy of existing average-responding meters.
