Later grey front version 4 of the Bel 8 track noise reduction system for analogue multi-track tape recorders.
Simultaneous encode / de-code system to remove undesirable tape hiss from machines running at 15 inches per second
NOT JUST FOR TAPE, GOT A NOISY EFFECT OR SYNTH? PUT IT THROUGH BEL NR TO REMOVE THE NOISE!
A very popular modular system in it's day, with phono connection on the rear panel.
All in good fully working condition, as pictured.