The API Select SR22 uses the same compressor circuitry as ATI' s Paragon analogue consoles, which merged with API in 1999.
Threshold, ratio and (make-up) gain can be adjusted continuously per channel. The SR22 offers ratios up to a maximum of 10:1. If used in stereo mode via the link function, the settings of the left channel determine the control behavior. Push buttons can be used to activate the patented Thrust circuit and Hard/Soft knee. Furthermore, the needle of the VU meter can optionally display the degree of level reduction or the output power.
For stereo operation, the processing of the left channel is not simply transferred 1:1 to the right channel, but an analog summing takes place beforehand. This way the response of the compressor is influenced by the actual stereo signal and not only by the left channel. In addition, the SR22 has a relay-controlled bypass, which avoids unnecessary signal paths of the clean signal in the unit.
The patented Thrust circuit activates a filter before the RMS detector that balances the energy level between low and high frequencies, as in typical side-chain applications. This creates a powerful sound that still sounds less compressed.