Ant64 Sound Architecture

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

The Lineage

Historically, several home computers unexpectedly became instruments:

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 FireStorm FPGA subsystem, with coordination and control provided by:

• Pulse Sequencer (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" — it is 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:

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

DDR3 / Flash → Sample Engine → Pitch / Rate Control → Mixer
                                      ↓
                               Loop / Crossfade / Granular Slice

• 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, and modern sampler workflows.

FM Synthesis (Enhanced)

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

Operator A (sine / sample / procedural)
    |  modulates
Operator B (sine / sample / procedural)
    |  modulates
Operator C --> Output

• 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 treats sound as a stream of tiny grains — each independently controllable.

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 Pulse

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:

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

Effects Architecture

Available Effects

Routing is flexible and fully programmable.

Reverb

Implemented using multi-tap delay lines, feedback networks, and damping filters:

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

Reverb parameters can be Copper-controlled, LFO-modulated, or MIDI-automated.

Copper-Controlled Audio

One of Ant64's most distinctive features.

Just as the Copper can alter graphics registers per scanline, it can manipulate audio at sample-accurate precision:

• 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, and characteristic of the best classic hardware systems.

Pulse Sequencer Integration

The Pulse Sequencer (RP2350) acts as the real-time musical interface:

Connectivity

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

Responsibilities

• MIDI parsing
• Sequencing & clocking
• Control data routing to FireStorm and SG2000

It communicates via SPI, presenting audio control as memory-mapped registers.

Analysis & AI-Assisted Features

Audio analysis is handled by the SG2000 CPU and its on-chip TPU ("AI chip"):

Audio In --> FPGA Capture --> SG2000 + TPU
                                  |
                       Note detection / Transcription
                       Pattern recognition
                       Intelligent sequencing

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

Comparison to Modern Synthesizers

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:

1. Powerful but understandable hardware — you can reason about what it does
2. Constraints that inspire creativity — limits breed innovation
3. Direct access to sound generation — no abstraction layers between you and the hardware
4. Tight coupling between audio, visuals, and interaction — sound is part of the machine, not an addon

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

Click here for in-depth audio plans »