The SA571 is a compander noise reduction chip, but it contains two VCAs which can be used independently. The chip is very useful to squeeze a bit of extra performance out of BBD-based circuits like delays, chorus, or flangers. It can also help reduce noise in PT2399-based delay circuits.
There is a short article about compander noise reduction with schematics for the compressor and expander stages that you might find helpful.
Please note that once remaining stocks of the SA571 compander are exhausted, we’ll supply the equivalent CoolAudio V571 instead. This chip is a pin-compatible and equivalent clone of the earlier chip.