API 525A; FET compressor in 500 series module format; attack adjustable from 15 microseconds to 15 milliseconds; 7 adjustable release modes (.05 to 2.0 seconds); Ceiling control simultaneously controls threshold and make-up gain; analog gain reduction VU meter in 1970s retro style; 2520 and 2510 operational amplifiers; discrete audio path circuitry; proprietary API output transformer; hardware bypass; balanced inputs and outputs; form factor: 500 series module