Sound Generator Unit 1

Status: Engineering prototype

ACTIVE DEVELOPMENTREVISION 1 PROTOTYPE

SGU-1

Nine-channel programmable sound generator module

A stereo audio-synthesis subsystem combining four-operator FM, flexible operator routing, per-channel filtering, hardware modulation and PCM sample playback.

View parametersDesign resources
Channels
9
FM operators
4 / channel
Sample memory
64 KiB
Audio output
48 kHz · Stereo
Gold SGU-1 programmable sound generator module render
SGU-1 REV 1 · PRODUCT RENDER

PRODUCT OVERVIEW

Features

  • Nine channels of four-operator FM synthesis
  • Stereo 48 kHz I²S audio path with analog line output
  • Eight operator waveforms: sine, triangle, sawtooth, pulse, noise, periodic noise, reserved and sample
  • Per-operator waveform shaping through WPAR
  • ESFM-style routing with independent output and modulation-input levels
  • Per-operator hard sync and ring modulation
  • OPN-style ADSR envelopes with sustain-rate control
  • Level-driven GATE plus one-shot TRIG retrigger and note-cut control
  • Per-channel resonant low-pass, band-pass and high-pass filtering
  • Continuous signed pulse width with 128 widths and two placements
  • Per-channel volume, frequency and cutoff sweep units
  • Per-channel phase-reset timer
  • Selectable saw, square, triangle and noise LFO shapes for AM and PM
  • 64 KiB dedicated PCM sample memory
  • Castellated module format for board-level integration
  • USB MIDI playback interface
  • 6502 player for SGM module format

Architecture and integration

SGU-1 is a new audio-synthesis device under development as part of the X65 Microcomputer Project. Its architecture combines established concepts from OPL/ESFM, OPM, SID, POKEY and Paula, including four-operator FM synthesis, flexible operator routing, per-channel subtractive filtering and hardware sweep units.

The device is implemented with a microcontroller and an audio CODEC. Together they produce a stereo 48 kHz I²S stream that the CODEC converts to an analog stereo line-level output. Developing a dedicated device provides the synthesis capabilities required by X65 without relying on advanced audio-synthesis chips that are no longer in production.

SGU-1 is intended for modern retro computers, original vintage machines, and modern embedded systems.

Host software and target-side playback may be adapted to the requirements of the system. sgu-tracker and the 6502 SGM player serve as the current development and proof-of-concept platform, demonstrating instrument definition, sequencing, effect control, module export, and playback as one possible integration path.

TECHNICAL DATA

Product parameters

Device typeProgrammable sound generator module
Audio channels9
FM architecture4 operators per channel
Operator waveforms8, including PCM sample playback
Operator routingIndependent output and modulation-input levels
EnvelopeAR / DR / SL / SR / RR, 5-bit rates
Channel filterResonant low-pass, band-pass and high-pass
ModulationHard sync, ring modulation, AM and PM LFO
Hardware sweepsVolume, frequency and filter cutoff
Audio output48 kHz, stereo sound
Signal pathI²S to analog stereo line out
ImplementationMicrocontroller and audio CODEC
PCM sample memory64 KiB
Host integrationCastellated board-edge I/O
Development controlSPI, USB-MIDI
Module formatSGM
Reference playback6502 player for SGM modules
DEVICESTATUS
SGU-1 REV 1Revision 1 evaluation hardware
NOT FOR SALE
Availability
Engineering samples
Production package
Castellated module
Design resources
In preparation

DESIGN RESOURCES

Documentation

DocumentDescriptionRelease status
Product briefArchitecture and system integration overviewIN PREPARATION
Register referenceHost control, synthesis and status register definitionsIN DEVELOPMENT
Gate and trigger behaviorLevel-driven GATE and one-shot TRIG semanticsIN DEVELOPMENT
Hardware design filesModule footprint, pin assignment and reference designPLANNED
Software toolssgu-tracker, C and 6502 playback softwareIN DEVELOPMENT

HARDWARE DEVELOPMENT

Prototype hardware

Three assembled SGU-1 prototype boards beside a match for scale
REV 1 prototype batchAssembled modules shown with a match for scale
Black and gold SGU-1 module component-side render
Component-side study