The AY-3-8910 family and its Yamaha variant, the YM2149 were used across a huge range of 8-bit and 16-bit computers. The chip clock frequency varies significantly depending on the host machine.
Because all tone generation, noise, and envelope timing are derived directly from the master clock, small differences in clock speed result in noticeable pitch changes.
This post summarises the clock rates used in classic systems.
ZX Spectrum 128K #
- Chip: AY-3-8912
- Clock speed: 1.7734 MHz
The Spectrum 128 derives its AY clock directly from the system clocking scheme (based around a 3.5469 MHz master clock). The AY is driven at half that rate.
Source: Sinclair hardware documentation and AY-3-8912 referencesSinclair Wiki AY-3-8912
Atari ST #
- Chip: YM2149F
- Clock speed: 2.0000 MHz
The Atari ST uses the Yamaha YM2149 variant, clocked at 2 MHz, derived from the system’s 8 MHz master oscillator.
This is one of the highest AY-family clock rates in mainstream machines.
Pentagon (Soviet ZX-Compatible Machines) #
- Chip: AY-3-8910 / AY-3-8912
- Clock speed: 1.75 MHz
The Pentagon clones (widely used in the Soviet demoscene) typically clock the AY slightly lower than the Spectrum 128.
This small reduction in frequency gives a slightly lower pitch compared to Spectrum tunes, which is important when comparing tracker music across Eastern European hardware.
Source: Sinclair Wiki AY-3-8912
MSX #
- Chip: AY-3-8910
- Clock speed: 1.7897725 MHz
MSX machines derive their AY clock from the NTSC colour burst crystal (3.579545 MHz / 2)
Source: msx.org AY-3-8910 Frequency Question
Amstrad CPC #
- Chip: AY-3-8912
- Clock speed: 1.0000 MHz
The Amstrad CPC family uses a much lower AY clock than Spectrum or MSX systems.
Source: CPC Wiki
Oric-1 / Oric Atmos #
- Chip: AY-3-8912
- Clock speed: 1.0000 MHz
Similar to the Amstrad CPC, Oric machines run the AY at 1 MHz, producing a distinctly different tonal character from other AY systems.
Source: https://docs.rs/psg/latest/psg/struct.PSG.html
Timex Sinclair 2068 #
- Chip: AY-3-8912
- Clock speed: 1.76475 MHz
A slightly unusual clock rate derived from the machine’s internal timing architecture.
https://sinclair.wiki.zxnet.co.uk/wiki/Timex_2000_series https://k1.spdns.de/Vintage/Sinclair/82/Timex%20Sinclair%202068/Timex%20Sinclair%202068.html
Vectrex #
- Chip: AY-3-8912
- Clock speed: 1.5000 MHz
To summarise, the main clock speeds we care about are (when it comes to replaying music available in VGP / pt3 formats):
| Clock Speed | System |
|---|---|
| 1.7734 MHz | ZX Spectrum 128 |
| 1.75 MHz | Pentagon |
| 1.7898 MHz | MSX |
| 2.0000 MHz | Atari ST |