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Experimenting with 1-Bit Sound on the ZX Spectrum for Multichannel Audio
Key points
- Implemented multichannel sound and chord playback on ZX Spectrum's 1-bit speaker.
- Recreated 1-bit PCM playback and experimented with PWM.
- Previous work involved Apple II and IBM PC 1-bit speakers.
- ZX Spectrum can achieve 16kHz playback with 1-bit PCM.
Developing 1-Bit Sound for ZX Spectrum
As part of a ZX Spectrum tour, a developer created routines to play simple tones and multichannel sound, including chords, using the machine's 1-bit beeper. This effort was inspired by earlier work on the Apple II and IBM PC's 1-bit speakers.
Techniques Explored
The development focused on multichannel sound through the 1-bit speaker. It also involved recreating simple 1-bit Pulse Code Modulation (PCM) playback and briefly experimenting with Pulse Width Modulation (PWM). These techniques informed the chord playback work.
Understanding 1-Bit PCM
PCM involves sampling a waveform and sending values to hardware for conversion into speaker voltages. The ZX Spectrum's speaker is either on or off, resulting in 1-bit PCM. While this can achieve a 16kHz playback rate, the 1-bit nature leads to significant distortion. The 48K ZX Spectrum's 3.5 MHz CPU clock was used for cycle counting in these experiments.
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Primary sources
GitHub michaelcmartin/bumbershoot GitHub breakintoprogram/archive-follin GitHub WordPress/WordPressReporting from
A developer implemented routines for multichannel sound, including chord playback, on the ZX Spectrum's 1-bit beeper. This work involved recreating 1-bit PCM playback and exploring PWM techniques, building on previous experiments with the Apple II and IBM PC's 1-bit speakers.