The RB-DMX4 is a digital mixer that can route or mix four mono inputs to four mono outputs, or two stereo inputs to two stereo outputs. Its internal sample rate conversion allows sources with different sample rates to be combined, while the output rate is set independently.

A flexible mix matrix, configured via four blocks of 4-way DIP switches, enables a wide range of routing and mixing options. The unit provides four digital mono inputs, selectable in pairs (1 & 2, 3 & 4) from AES/EBU (XLR), S/PDIF (phono), or TOSlink optical sources using front-panel buttons. Button colour indicates sync status: unlit when synchronised, flashing green/red when not.

Each input includes a trim control for level adjustment, ensuring balanced mixing of sources with different signal levels. Audio presence LEDs indicate input activity, with one LED per channel, while additional LEDs around the monitor button show output levels. Output gain can also be increased via a dedicated mode.

Two stereo outputs are available simultaneously on AES/EBU, S/PDIF, and TOSlink connectors. Output sample rates are selectable (32kHz to 192kHz) via rear-panel DIP switches. Synchronisation options include TTL wordclock (BNC), AES/EBU, or optional video sync boards. A rear DIP switch block selects the sync source and operating mode, with the monitor button flashing to indicate loss of sync.

Four sync modes are available:

• Master Mode: Uses the internal clock only.

• Auto Sync Mode: Follows the selected sync input, reverting to the internal clock if absent.

• Auto Lock Mode: Outputs only when locked to a sync signal; otherwise falls back to the nearest internal frequency.

• Slave Mode: Follows the sync input and disables output if sync is lost.

A front-panel monitor socket with level control allows channel monitoring, with selectable channels via a push button that can also provide up to 12dB gain. A rear DIP switch enables 12dB attenuation if required. The unit can operate in mono or stereo mode, with stereo mode linking input pairs for consistent level control.

For reliability, the RB-DMX4 includes a passive bypass: if power fails, inputs 1 & 2 are routed directly to outputs 1 & 2, and inputs 3 & 4 to outputs 3 & 4. (TOSlink outputs are muted in this condition.)