Taking its place alongside the API Audio family of VCA-based compressors, the 527A is a 500-series compressor/limiter module sporting selectable feedforward (New) and feedback (Old) compression modes. Along with selectable hard- or soft-knee compression and the patented THRUST circuit for extra punch in the low frequencies, the 527A is a versatile studio compressor.
Onboard controls include Threshold (+10 to -20 dBu), Ratio (1:1 to Infinity:1), Attack (1 to 25 ms), Release (0.3 to 3 seconds), and Output Level, all on continuously variable, center-detented knobs for easy reset. You also get two-way switches for selecting meter in/out, stereo link, New or Old compression modes, hard or soft knee, and the Thrust circuit. The In button lets you select between soft and hard mechanical relay bypass. Discrete 2510 and 2520 op-amps ensure the smooth and consistent sound signature of the API analog tone. Finally, the onboard 10-segment LED meter measures both gain reduction and output level, and you can read a single LED overload indicator to see when signals exceed +21 dBu.
In a feedback compressor (Old), the RMS detector gets its signal from the output of the gain reduction device (VCA). This is how older API 525, 1176-type, and 660-type compressors work. This yields a smoother, softer, more transparent sound.
- In: Press to engage the compressor in signal path (switch illuminates)
- Out: Press to remove the compressor in signal path (switch unlit)
- Bypass: Press and hold to engage the relay-based hard bypass (switch illuminates in red)
When connected together and the Link switches are engaged, the DC control voltages from all units are summed together. This results in the same control changes being applied to all compressors.