The ES-4 is a Eurorack format module which converts a standard S/PDIF input to five channels of control voltage.

Two of the five channels are calibrated to provide over 5 octaves of 1V/octave pitch CV.

The remaining three channels are general purpose outputs (for use as e.g. gates, envelopes, LFOs) and each have a nominal range of 0-10V or ±5V (user selectable).

Since S/PDIF is a stereo-only format, the encoding of the five channels on to two is handled by software provided as part of Expert Sleepers Silent Way.

The ES-4 will connect to any audio device using the S/PDIF standard. This includes the digital audio output provided as standard on all recent Macs.

The ES-4's specifications are as follows:
Panel width: 8HP
Module depth: 51mm
Digital input: coaxial S/PDIF, standard rates up to 192kHz
Digital output: coaxial S/PDIF
Analogue outputs: 5x 3.5mm jacks, DC-coupled
Output voltages
Channels 1-2: 0-5.3V (when trimmed for 1V/octave response)
Channels 3-5: 0-10V or ±5V (jumper selectable per channel)
D/A conversion: 8 bit, using high precision Analog Devices DACs
Indicators: LED for S/PDIF sync lock; 2 LEDs per channel on channels 3-5 indicate output voltage (+ve/-ve)
Expansion
5 headers for connecting ES-4 Gate Expander modules (see below)
Digital audio I/O header (I2S format) for future expansion
Current draw: 50mA on the +12V rail, 20mA on the -12V rail (70mA total)

While the ES-4 is specified to run at 192kHz, at the time of writing this has not been tested. Operation up to 96kHz however has been tested and verified.

The front panel is drilled for both Doepfer and Analogue Systems mounting holes (using a 'slot' rather than a single round hole).

The power connector is a Doepfer standard 16 way IDC, with -12V furthest from the top of the board.