DPA Series — DPA80/DPA100 Operating Instructions Page 67taxPeak LimiterThe main limitation with traditional dynamics control is the inability of the processing to reacttruly instantaneously to the signal. One of the most significant advantages of digital signalprocessing over analogue is the ability to delay the audio signal precisely and withoutextensive complex hardware. The entire domain of digital signal processing is based aroundthe combination of delaying, multiplying, and accumulating numbers (representing samplesof audio) to implement all the filters and dynamics processing we have come to expect today.In the case of dynamics processing, being able to delay a signal allows the processor moduleto delay the main signal in relation to the sidechain (the signal being monitored relative to thethreshold), so that it can compensate for peaks prior to the arrival of the main signal.Consider the situation of a monitor engineer listening to a band perform. Having no access todynamics processors, he has had to resort to manually ‘riding the faders’ in an attempt tokeep control of the levels. Should the level of one of the channels on his desk reach anunacceptably high level, he will turn it down appropriately.There is a hidden sidechain inoperation even in this case.The main signal path is fedthrough the monitor desk andthe gain controlled byadjusting the fader. Thesidechain is formed by thefeedback path between theengineer’s ears checking thelevel and his brain instructinghis hand to turn the faderdown if the volume goes overthe threshold he has chosen.In this case, the delay between the signal actually going over the threshold, the engineerregistering the situation, and then turning the signal down will be in the order of severalhundred milliseconds at best. This will only be true if he is not distracted — in reality, it maybe several seconds before any gain reduction is imposed on the signal to bring it undercontrol. Audio Input(Signal beingmonitored) Gain ControlElementOutput toAmp/SpeakerSystemFeedback Path from Monitor Engineer’s Ears to Handforming Sidechain Control Signal
