Ahhh - dbx !
The best noise-reduction system, sadly not able to shake to Dolby monolith. But it gave reel and cassette recorders such as the RS-M253X or RS-M275X a truly unbelievable sound quality and dynamic range.
The RS-M253X sports all the possible features of a 1982 high-end deck : all sorts of displays, modes and functions plus - the usual Dolby B and Dolby C. If a three-head, it is however only a 2-motor deck...
But the dbx circuit was here jointly developed by Technics (Matsushita) and the dbx labs. Switches for disc / tape source are present to properly decode dbx-encoded LPs or dbx-encoded tapes.
The rec and play heads are AX : "amorphous non-cristalline atomic arrangement" ; the erase head is a double-gap Sendust.
Also present : automatic tape/source monitoring (defeatable), bias fine-tuning, big multi-coloured 18-segment FL display, 4-digit digital counter, 3-digit tape counter (through a Hall IC that detects reel rotations), 20-song music selection, 16x repeat, record mute with time display, microprocessor controlled feather-touch transport controls, automatic tape selector, high-linearity microphone amp with automatic input level and optional RP-9645 wired remote control.
And a nice design as well, discreet but typical of those coloured days.
A somewhat simplified version (no bias adjust and 2-head only) of the RS-M253X was available as late as 1988 under the RS-B70 name...