Audio circuit uses the 2510 and 2520 Discrete Op Amps with transformer output Continuously variable detented Threshold control Continuously variable detented Attack and Release controls Continuously variable detented Ratio control Output Fader level control 10 segment VU/Gain Reduction meter with selector switch Overload LED "Link" switch for multiple unit interdependent compression linking "New"/"Old" switch for feed-forward or feed-back compression "Hard"/"Soft" compression curve knee switch Patented THRUST® switch for frequency dependent side chain control "IN" switch with hard relay bypass when in the "Out" position The API 527 takes it's place alongside the family of API VCA based compressors, the 225L and the 2500 Stereo Bus Compressor. Anyone familiar with those units will immediately be at home with the 527. Features common to the line like "feed forward" (NEW) and "feed back" (OLD) gain reduction methods selectable on the front panel, provide a choice of "that old way", or "the new way" of compression, for the highest level of flexibility in signal gain control. The "old way" or Feed-Back method is what most of the classic compressors used for the gain control circuit. The "new way" gain reduction is more typical of the newer VCA type compressors that rely on RMS detectors for the gain control voltage. There is a "SOFT"/"HARD" switch for an "over-easy" type compression resulting in a very natural, uncompressed sound or a typical sharp knee type that lends itself to a much more severe limiting effect. The Threshold control sets the initial operating parameter. The 527 can be operated with signal input levels from +10 dBu to -20 dBu. The 527 features an Output fader control that ranges from minus infinity to +10dB, and output capability is +28 dBu through our 2520 discrete amplifier and a large API output transformer. The output level remains fairly constant regardless of the threshold or ratio control, much like the "more/less" Ceiling control on the API 525 compressor. This allows for live adjustments without any noticeable gain changes in the program level. The patented THRUST function can be switched in and out via the front panel as well, applying a high pass filter before the RMS detector circuit that preserves that punchy bottom end.