The BSS DPR-504 is a classic 1RU 4-channel noise gate designed for high-performance audio, featuring electronically balanced I/O, parametric key filters, and fast attack (20µs) or auto-tracking modes. It provides 70dB/20dB range gating, with each channel featuring independent threshold, release, and linking capability. Key Specifications: Audio Inputs/Outputs: Electronically balanced XLR connectors, 12kOhm input impedance, >50dB CMRR, +20dBv max level. Performance: < 0.05% THD (20Hz-20kHz), >90dB crosstalk, 20Hz-20kHz frequency response (+/-1dB). Gate Controls: Threshold: Variable +20dBv to -50dBv. Attack: Switchable FAST (20µs) or AUTO (40µs-5ms). Release: Variable 1ms to 3s. Key Filter: Variable 30Hz to 15kHz. Dimensions/Weight: 482mm x 44mm x 282mm (19" rackmount), 5kg (11lbs). Power: Switched 120/240V, 50/60Hz. The unit, often used for drums and complex audio sources, includes a dedicated "Key Listen" mode and a "Gate Open" LED indicator. In very good condition. ALL LED lights work.