RME Digiface USB 66-Channel ADAT Optical USB Audio Interface

RME Digiface USB: 32-Channel Optical Expansion in a Tiny Box

The RME Digiface USB is an ultra-compact, bus-powered USB 2.0 audio interface that turns four optical ADAT ports into 32 inputs and 32 outputs of digital I/O, for 66 channels total. Built for engineers who work with ADAT-equipped preamps and converters, it aggregates that optical gear into a single laptop connection weighing about half a pound. A high-quality headphone and line output, SteadyClock timing, and TotalMix FX routing round out a device that is far more capable than its size suggests. There are no analog inputs, so this is a pure optical powerhouse designed to expand a rig's channel count. For anyone with a stack of ADAT gear and no way into the computer, it is the smallest, cleanest answer.

Four Optical ADAT Ports for 32x32 I/O

The Digiface USB carries four optical TOSLINK ports for input and four for output, each capable of running 8-channel ADAT for a total of 32 channels in and 32 out. ADAT is an optical protocol that multiplexes eight channels of digital audio down a single optical cable, so four ports deliver a full 32-channel optical snake to and from the computer. Any of the ports can alternatively run SPDIF for stereo digital sources. That density of optical I/O is what lets a device this small replace a much larger interface for channel expansion.

Automatic Format Detection and SMUX

Each optical port automatically detects its incoming format and supports SMUX and SMUX4 for high sample rates, so the interface adapts to whatever ADAT or SPDIF signal it receives. SMUX (sample multiplexing) spreads a high-sample-rate stream across multiple ADAT channels, which is how ADAT carries 96 kHz and 192 kHz audio despite its original 48 kHz design. At 192 kHz, each optical port carries eight channels via SMUX4. This automatic format handling means an engineer can connect mixed gear without manually configuring every port.

High-Quality Headphone and Line Output

A single 1/4-inch TRS output doubles as a high-quality line output and a capable headphone amplifier, giving the otherwise all-optical interface a real monitoring path. Despite the device's tiny footprint, RME fits a clean, low-noise output stage that drives studio headphones with authority. That lets an engineer monitor any of the 32 optical channels directly from the box without a separate converter or amplifier. It is the detail that makes the Digiface USB usable as a standalone monitoring hub as well as an expander.

SteadyClock Timing

RME's SteadyClock timing keeps the Digiface USB's conversion and optical streams locked with very low jitter, even when following an external ADAT or SPDIF source. Clock jitter is small timing error in the digital sampling process, and reducing it preserves stereo imaging and keeps distortion low across all 32 channels. Because SteadyClock regenerates a clean internal clock, the interface stays stable whether it acts as clock master or slaves to incoming optical audio. In a multi-device optical rig, that timing stability prevents the clicks and dropouts that plague poorly clocked systems.

TotalMix FX and Ultra-Compact Build

TotalMix FX runs on the interface to provide near-zero-latency monitoring and full matrix routing among all 32 optical channels and the headphone output. The entire device is bus-powered over USB 2.0 and weighs about 0.49 pounds, small enough to tape to a laptop lid or drop in a bag with a couple of ADAT converters. Running its routing in hardware keeps the host computer free while giving the engineer console-style control. That blend of huge optical channel count, tiny size, and bus power is exactly what makes the Digiface USB a studio favorite.

Optical Expansion Applications

The Digiface USB is built for expanding a DAW with ADAT gear, aggregating optical preamps and converters, and providing portable optical recording and monitoring. Typical uses include connecting banks of ADAT mic preamps for tracking a full band, adding 32 channels of I/O to a laptop rig, and serving as a headphone monitoring hub. With no analog inputs of its own, it pairs naturally with the optical converters an engineer already owns. For anyone who needs maximum optical channel count from the smallest possible box, it is the definitive tool.