Converting Oktalyzer (OKT) Modules to WAV: Amiga 8-Channel Chiptune Synthesis

Released in 1989 by German programmer Armin Sander, Oktalyzer was an engineering breakthrough for the Commodore Amiga. While the Amiga's custom sound coprocessor (Paula) natively featured only 4 hardware DMA audio channels (2 panned hard left and 2 panned hard right), Oktalyzer introduced software mixing to squeeze 8 polyphonic channels out of the standard Amiga 500.

In this deep dive, we explore the chunk-based architecture of .okt files, the mechanics of Amiga PAL period calculation, and how convrtr synthesizes Oktalyzer modules into studio-grade 16-bit 44.1kHz stereo WAV audio entirely within your browser.

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1. The OKTASONG Chunk Structure

Oktalyzer modules follow an IFF-like chunk-based layout starting with the 8-byte ASCII format signature OKTASONG:

| Chunk ID | Name | Description | |---|---|---| | CMOD | Channel Modes | 8 bytes configuring 4-channel vs 8-channel voice pairings | | SAMP | Sample Headers | 32-byte headers per sample: name, length, loop start, loop length, and volume | | SPEE | Default Speed | Initial tick tempo per pattern row (typically 6 ticks) | | SLEN | Song Length | Number of orders in the arrangement playlist | | PLEN | Pattern Length | Total count of distinct patterns stored in the file | | PATT | Order List | Array of 16-bit indices mapping arrangement orders to pattern numbers | | PBOD | Pattern Body | Pattern row cells: 64 rows with note, instrument, and effect commands | | SBOD | Sample Bodies | Raw 8-bit signed mono PCM waveforms (-128 to 127) |

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2. Amiga Paula Period and Frequency Synthesis

In classic Amiga audio architecture, sample pitch is governed by clock division against the PAL master frequency (3,546,895 Hz). The sound hardware counter decrements by 1 every clock cycle until it reaches the note period:

Frequency (Hz) = 3546895 / Period

For middle C (note C-3), the PAL period is 428, producing an audio frequency of approximately 8287 Hz:

function noteToPeriod(note: number): number {
  if (note < 1) return 0;
  const semitoneDiff = note - 25;
  const period = Math.round(428 * Math.pow(2, -semitoneDiff / 12));
  return Math.max(50, Math.min(6000, period));
}

By computing step = freq / sampleRate, convrtr resamples 8-bit signed PCM samples across any target output sample rate (such as 44.1 kHz or 48 kHz) using smooth linear interpolation.

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3. 8-Channel Stereo Panning

To reproduce the authentic acoustic stage of the Amiga, channels are panned across left and right stereo channels according to their Paula hardware channel pairings:

• Left Channels: 0, 3, 4, 7
• Right Channels: 1, 2, 5, 6

A configurable stereo separation parameter allows listeners to adjust the mix from authentic hard-panned stereo separation down to balanced modern headphone listening.

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4. 100% Private Offline In-Browser Conversion

convrtr performs all IFF chunk parsing, oscillator stepping, sample interpolation, and WAV packaging directly in client-side TypeScript. Your retro tracker files are processed purely in local memory with zero server uploads.