Model 439, a two-channel attenuator-amplifier, has a gain rate of 118 dB in one dB steps ( 78 dB to +40 dB). The gain is set by a front panel rotary encoder and displayed on an LCD. Each channel's gain can be set independently or they can be set together depending on the position of the SET GAIN switch. A power amplifier is included to drive a stereo headphone for audiometric testing or other use. The design uses low noise op amps and clock noise is eliminated by putting the microprocessor into sleep mode when it is not programming the gain.