What is Parallel Compression? Standard compression is usually done with the compressor inserted on the track so the result is a wet or processed signal. Parallel compression can be done with an auxiliary or by duplicating or splitting a signal and sending one signal to a compressor and leaving the other unprocessed. When the two mix back together an amazing thing happens. The peaks from the unprocessed signal mask the compressed peaks of the compressed signal and the valleys of the compressed signal mask the valleys of the unprocessed signal. So the result is what gives this the alternate name of ‘upward compression’ where the lower signal is louder but the peaks are left untouched. This technique can be used in mixing or mastering and many high-end processors provide a wet/dry knob to let you do this effect very easily.