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.

SOUND DEMONSTRATIONS

Listen to SGU-1 live

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 RESALE
Availability
Engineering samples
Production package
Castellated module
Design resources
In preparation
CORESTATUS
SGU-1 C SOFTCOREPortable functional implementation
AVAILABLE ↗
Core interface
sgu.h ↗
Implementation
sgu.c ↗
Hardware path
VHDL design reference

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
SGU-TrackerDedicated online instrument editor, sequencer and playback environmentAVAILABLE ↗
Source repositorySGU-1 hardware and software development sources on GitHubAVAILABLE ↗

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