This is an audio rack-mounted signal processor, most likely a stereo graphic equalizer or audio dynamics processor. It is designed for professional PA sound systems, studio equipment, and live sound setups.
From the front panel, controls labelled STEREO, MIC, EQ, MONO, a
Stereo: Controls or adjusts the stereo audio signal.
MIC: Likely controls the microphone input or level.
EQ (Equalizer): Adjusts low, mid, and high frequencies to shape the sound.
MONO: Controls the mono output level.
MASTER: Controls the overall output level.
LED indicators: Show signal levels and possible clipping.
Power switch: Turns the unit on and off. It can also be used as a mixer.