What we have here is a  DBX 1231.  The 1231 is a professional-grade dual-channel, 31-band graphic equalizer engineered for high-demand sound reinforcement, touring, and permanent studio installations. Housed in a rugged 3U rackmount chassis, it features 45 mm medium-throw faders for highly precise tactile frequency adjustments across standard ISO 1/3-octave centers. Known for its exceptional signal transparency and quiet operation, the unit delivers a broad frequency response from 10Hz to 50kHz alongside a dynamic range of up to 115dB.

Key Performance Features

• Selectable Boost/Cut Range: Features a recessed front-panel switch to toggle between a subtle ±6dB range for precision acoustic tuning and a more aggressive ±15dB range for live feedback notches.

• Low-Cut Filter: Equipped with a switchable 40Hz 18dB/octave Bessel high-pass filter designed to eliminate stage vibrations, AC rumble, and mic handling noises without impacting neighboring bass frequencies.

• Fail-Safe Relay Bypass: A power-off hardwire relay bypass keeps signal chains uninterrupted during a power failure, complemented by a 2-second power-up delay to safeguard speakers from transient thumps.

• Advanced Noise Isolation: Integrates RF-filtered inputs/outputs, a magnetically isolated internal power transformer, and a chassis ground-lift switch to instantly target and suppress ground loop hum.

I have two of these units for sale here on Reverb.