One of the first new units in the BSS Audio's Opal Series is the DPR-422 Dual Compressor/De-Esser. The 422 features electronically balanced inputs and outputs, and comprehensive signal metering for rapid system monitoring. The side chain inserts are also balanced with separate connections. To facilitate matching both professional and semi-professional equipment, inputs and outputs on the DPR-422 can be switched to operate at +4dBu or -10dBV nominal levels.

The DPR-422 Dual Compressor/De-Esser compressor section uses a double side-chain circuit with only a subtractor and gain control in the main signal path. Broadband or advanced frequency selective compression is produced by subtraction from the main signal. Broadband de-essing adds to normal compressor functionality with the ability to compress the whole signal when high frequency components exceed the preset de-ess threshold level. For greater precision in demanding applications, it can be set by the main compressor controls. The De-Ess HF mode uses all the compressor control circuitry to create a dedicated, frequency-selective de-esser channel compressing high frequency signals while leaving low frequency content unmodified.

Other professional features include: stereo link that ties the two channels' VCA side-chain circuits together for proper stereo image preservation; progressive knee compression characteristics; attack, release and ratio controls; AUTO mode for quick "on the fly" setting; and a side-chain "listen" switch.