Converting AMF Tracker Modules to WAV: Advanced Module Format Audio Synthesis

In the early 1990s, the IBM PC demoscene was undergoing a dramatic sonic renaissance. While the Commodore Amiga's hardware audio chipset was strictly limited to four 8-bit digital sound channels, PC sound cards like the Gravis UltraSound and Creative Sound Blaster 16 unlocked multi-channel polyphony.

Finnish demoscene programmer and musician Otto Chrons developed the Digital Sound & Music Interface (DSMI) library and the Advanced Module Format (AMF). AMF powered legendary PC music tracker programs including ASYLUM Music Format Tracker and was chosen by game developers for soundtracks like Star Control II.

Files encoded in this tracker format carry the .amf extension.

This technical guide unpacks the binary structure of AMF revisions (v1.0 through v1.4 and ASYLUM 1.0), details the packed pattern track architecture, and explains how convrtr's AMF to WAV converter synthesizes authentic 16-channel DOS module soundtracks into studio-quality 16-bit stereo WAV files entirely within your web browser.

The AMF File Header

An AMF file begins with a distinct multi-byte signature identifying its format version:

| Magic Bytes | Version | Description | | :--- | :--- | :--- | | "AMF" (0x01 to 0x0E) | AMF v1.0–v1.4 | Otto Chrons DSMI tracker format | | "ASYLUM " (0x20) | ASYLUM 1.0 | ASYLUM Music Format tracker |

Following the magic signature, the header stores global playback parameters:

• Song Title: 32 ASCII characters describing the track name.
• Sample Count: Number of digital PCM audio instruments (up to 64).
• Order Count: Total sequence entries determining pattern progression.
• Track / Channel Count: Number of simultaneous playback channels (up to 16).
• Initial Tempo & BPM: Default playback speed and ticks per row.

Sample Headers and Audio Memory

Each digital sample is defined by a structured header table specifying its memory footprint and loop behavior:

• Sample Type: Unsigned or signed 8-bit PCM samples.
• Sample Length: Length in bytes of the raw waveform data.
• Loop Start & End: Sample offsets for sustained notes and looping pads.
• Volume & Finetune: Base playback amplitude (0–64) and frequency tuning adjustments.

Unlike Amiga MOD files where samples were limited to 64KB, AMF allowed samples to span arbitrary memory buffers suitable for PC extended memory (XMS).

Channel Track Packing

AMF achieved superior compression compared to uncompressed MOD files through its independent track structure. Rather than storing empty rows across all channels in a global matrix, AMF decomposes patterns into reusable column tracks:

Pattern Matrix = [Channel 0 Track Index, Channel 1 Track Index, ..., Channel N Track Index]

Within each track, events are encoded as compact byte streams:

1. Note and Octave: 1–83 semitones mapped to standard ProTracker frequency tables.
2. Instrument Index: Reference to the sample header.
3. Volume and Effect Commands: Arpeggio, portamento, vibrato, and volume slides.
4. Empty Row Compression: Consecutive silent rows are stored as single repeat codes.

Client-Side In-Browser Synthesis

convrtr's AMF audio engine parses the module header, decodes all packed channel tracks, and executes an authentic 16-channel software mixer running at 44.1 kHz. Each channel interpolates 8-bit PCM waveforms using linear resampling, adjusts stereo panning, and generates a lossless 16-bit stereo WAV buffer.

No plugins, command-line utilities, or cloud uploads are required. All synthesis runs in pure client-side TypeScript inside your browser.