Digital Audio on the ZX Spectrum's 1-Bit Beeper
a day ago
- The article details a method to produce high-quality digital audio through the ZX Spectrum's 1-bit beeper using precise timing and a jump table technique.
- The technique was refined through two failed attempts involving delay loops and dynamic delays before achieving success with a macro-based jump table.
- The final playback code uses cycle-counted instructions, shadow register preservation, and a 16-entry jump table to output 4-bit PCM audio at 8kHz, with amplification applied.
- Practical limitations include very soft sound without external amplification and high RAM usage (nearly all available memory for longer samples).
- Related work includes Dmitry Milk's CORE5 engine (using 256-entry jump tables and full 8-bit audio) and Michael J. Mahon's RTSynth for the Apple II, both employing similar pulse-width modulation principles.
- The Spectrum's straightforward hardware design contrasts with other systems like the C64, requiring direct timing control rather than exploiting undocumented behaviors.