Converting AdLib ROL Music to WAV: Emulating 1980s PC FM Synthesis

Before the Sound Blaster became the household name for PC multimedia, there was the AdLib Music Synthesizer Card. Released in 1987 by Ad Lib Inc. of Quebec, Canada, this ISA expansion card revolutionized IBM PC audio by replacing the abrasive single-frequency internal PC speaker with the Yamaha YM3812 (OPL2) sound chip.

To compose music for this groundbreaking hardware, AdLib provided the Visual Composer software, which saved songs in the proprietary .rol format.

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1. The Structure of an AdLib ROL File

An AdLib ROL file stores musical arrangement instructions tailored to the 9-channel FM synthesis hardware:

• Header Block: Stores major/minor file format version identifiers, timing resolution (ticks per beat, default 120), beats per measure, and nominal playback tempo.
• Instrument Mapping: Defines which AdLib BNK or standard FM instrument timbre applies to each of the 9 melodic voices.
• Track Event Streams: Sequential event records describing channel assignments, MIDI pitch note indices (0..96), duration counts in clock ticks, and volume velocity parameters.
• Rhythm Mode: Optional configuration toggling 6 melodic channels plus 5 percussion channels (bass drum, snare, tom-tom, top cymbal, hi-hat).

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2. Emulating 2-Operator FM Synthesis in Modern Web Browsers

Because modern operating systems lack physical Yamaha YM3812 sound hardware, convrtr performs authentic 2-operator FM synthesis directly in client-side TypeScript:

1. Carrier and Modulator Oscillators: Simulates phase modulation where the output of operator 1 (the modulator) dynamically modulates the instantaneous phase of operator 2 (the carrier).
2. Frequency Calculations: Accurately derives pitch frequencies using standard equal-temperament tuning curves referenced against 440 Hz standard pitch.
3. ADSR Envelope Shaping: Generates authentic linear attack, decay, sustain, and exponential release envelope curves for each active voice.
4. 16-bit Stereo PCM Export: Renders the combined 9-channel mix into studio-standard 44.1 kHz or 48 kHz 16-bit WAV audio via writeWav.

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3. Pure Client-Side Privacy and Preservation

Retro computing preservation should never depend on cloud services or external servers. With convrtr, your vintage AdLib .rol music archives are synthesized 100% inside your web browser sandbox with zero network requests.