DIY Audio Compressor with VCA IC

Built an audio dynamics compressor using the THAT2162 VCA IC and an Arduino as the gain control computer. This taught me a lot about control loop design for audio.

The compressor architecture: input audio goes into the VCA (variable gain amplifier), the output goes to a peak detector, the Arduino reads the peak detector via ADC, computes the required gain reduction, and writes to a DAC that controls the VCA gain pin. Attack and release time constants are implemented in firmware with adjustable RC-equivalent digital filters on the gain control signal.

The THAT2162's gain is in dB, linear with control voltage — 30mV per dB. This simplifies the gain calculation: just work in dB throughout. Ratio (2:1, 4:1, ∞:1) is implemented as a slope in the gain reduction curve. A soft knee is implemented by blending the uncompressed and compressed gain in the threshold region.