API Audio 2500+, Legacy Stereo Bus Compressor with blend function, API 2520 op-amp, Adjustable threshold -20db to + 10db, Selectable ratio, attack and release times, Patented highpass filter in the detector path, With variable link between left and right channel, Selectable ""old"" and ""new"" envelope curve, Typical behaviour as with API525, 1176 and Fairchild, Auto or manual ""Gain make up"", Sidechain inputs, Ideal sum compressor