Ant64 Sound Architecture

The Ant64 audio system is not designed merely to play sound — it is designed to invite musical creation.

Historically, several home computers unexpectedly became instruments:

  • The Commodore 64, through the SID chip, spawned an entire generation of musicians.
  • The Atari ST, through built-in MIDI and deterministic timing, became the heart of countless studios.
  • The Amiga, through sample-based audio and trackers, created a new culture of electronic composition.

In each case, the designers did not explicitly set out to build a “music workstation”. Instead, they created systems where sound was immediate, programmable, constrained, and deeply tied to the machine itself.

Ant64 intentionally follows this lineage — not by emulation, but by evolution.

Sound on Ant64 is:

  • Hardware-first
  • Deterministic
  • Memory-mapped
  • Deeply programmable
  • Capable of misuse and experimentation

These qualities are essential for a system to become a creative platform rather than a closed appliance.

Architectural Overview

Audio generation on Ant64 is primarily handled by the Razz FPGA subsystem, with coordination and control provided by:

  • Jazz (RP2350) – MIDI, audio input, live control, sequencing
  • SG2000 RISC-V – composition, analysis, AI-assisted workflows
  • Copper & Update Units – real-time, timeline-driven audio manipulation

The FPGA audio engine is not a fixed “sound chip”, but a reconfigurable, multi-paradigm audio fabric.

Voice Architecture

Polyphony

The baseline Ant64 configuration supports 128 simultaneous hardware-mixed voices, with headroom for more depending on sample rate, effects usage, and synthesis mode.

Voices are not uniform; each voice can independently operate in one of several modes:

  • Sample playback
  • FM synthesis
  • Hybrid FM + sample operator
  • Granular synthesis
  • Procedural waveform generation
  • Phase-locked or time-stretched playback

Voices are mixed in hardware, with per-voice spatialisation and effects routing.

Voice Components

Each voice may include:

  • Amplitude Envelope (ADSR or multi-segment)
  • Pitch Envelope
  • Per-voice filter (LP / HP / BP, resonant)
  • Per-voice LFOs (multiple, routable)
  • Stereo positioning
  • Velocity and aftertouch modulation
  • Copper-controlled parameter overrides

This mirrors — and in many cases exceeds — the per-voice control found in modern synthesizers.

Synthesis Modes

Sample-Based Synthesis

  • High-quality samples stored in DDR3 or flash
  • Variable playback rate
  • Independent pitch and duration control
  • Looping, cross-fades, and granular slicing

This enables:

  • Fairlight-style instruments
  • MOD/XM-style trackers
  • Modern sampler workflows

FM Synthesis (Enhanced)

Ant64 supports FM synthesis with sample-based operators, not limited to sine waves.

Key features:

  • Operators may be:
    • Sine
    • Procedural waveforms
    • Arbitrary samples
  • Configurable operator graphs
  • Feedback paths
  • Envelope and LFO modulation per operator

This allows:

  • Classic DX-style FM
  • Acid-style basslines (303-like)
  • Hybrid FM/sample textures impossible on vintage hardware

Granular Synthesis

Granular synthesis is implemented using the existing audio update units:

  • Samples are divided into grains
  • Grain position, duration, pitch, and density are hardware-controlled
  • Real-time modulation via Copper or Jazz

Granular processing enables:

  • Time-stretching without pitch change
  • Textural soundscapes
  • Evolving pads and ambiences

Phase Vocoder / Time-Domain Processing

Ant64 supports pitch-independent time manipulation using hardware-assisted resampling and phase-aligned processing.

This allows:

  • Changing pitch without altering length
  • Changing length without altering pitch
  • Spectral-style transformations

While full FFT-based vocoding is handled in software (SG2000 + TPU), the FPGA provides the real-time primitives required for live playback.

Effects Architecture

Effects Block

Ant64 includes a dedicated effects processing block, operating alongside the mixer.

Supported effects include:

  • Reverb
  • Delay / Echo
  • Chorus / Flanger
  • Distortion / Saturation
  • Filters and EQ

Effects may be:

  • Per-voice
  • Per-group
  • Global

Routing is flexible and programmable.

Reverb

Reverb is implemented using:

  • Multi-tap delay lines
  • Feedback networks
  • Damping filters

This produces:

  • Room, hall, and plate-style reverbs
  • Low-latency performance suitable for live play
  • Minimal FPGA resource usage

Reverb parameters can be:

  • Copper-controlled
  • LFO-modulated
  • MIDI-automated

Copper-Controlled Audio

One of Ant64’s most distinctive features is Copper-controlled audio.

Just as the Copper can alter graphics registers per scanline, it can:

  • Change voice parameters at precise times
  • Modulate filters rhythmically
  • Trigger events sample-accurately
  • Synchronize sound tightly with visuals

This enables effects that are:

  • Extremely precise
  • Impossible in software alone
  • Characteristic of classic hardware systems

Jazz Integration (MIDI & Control)

The Jazz RP2350 acts as the real-time musical interface:

  • USB MIDI
  • DIN / DOUT /DTHRU MIDI (Creative Edition)
  • Analog control pots
  • Mouse and external controllers
  • Live audio input

Jazz handles:

  • MIDI parsing
  • Sequencing
  • Clocking
  • Control data routing

It communicates with Razz and the SG2000 via SPI, presenting audio control as memory-mapped registers.

Analysis and AI-Assisted Features

Audio analysis (such as note detection, transcription, and pattern recognition) is handled by:

  • SG2000 CPU
  • On-chip TPU ("AI chip")

This allows:

  • Converting samples to note data
  • Assisting composition
  • Intelligent sequencing and rhythm generation

The FPGA does not perform heavy analysis — it focuses on deterministic sound generation.

Comparison to Modern Synthesizers

At a system level, Ant64 compares favourably to:

  • High-end digital synthesizers
  • Hybrid grooveboxes
  • Modular software synths

Key differences:

  • No plugin latency
  • Deterministic timing
  • Hardware-visible architecture
  • Deep programmability
  • Price point significantly lower

Unlike many modern synths, Ant64 is also:

  • A full computer
  • A graphics workstation
  • A programmable hardware platform

Creative Intent

Ant64 is designed so that unexpected uses of sound are not only possible, but encouraged.

Just as the C64, Atari ST, and Amiga were adopted by musicians for reasons their designers did not fully anticipate, Ant64 aims to create the same conditions:

  • Powerful but understandable hardware
  • Constraints that inspire creativity
  • Direct access to sound generation
  • Tight coupling between audio, visuals, and interaction

The goal is not merely to reproduce classic sound — but to create the environment in which the next musical subculture can emerge.

Important: The Ant64 family of home computers are at early design/prototype stage, everything you see here is subject to change.