AY is the nickname of the AY-3-8910 programmable sound generator family.
The Amstrad CPC sound processor is more exactly the AY-3-8912.
This chip was very popular and was used in a lot of machines.
MSX, ZX Spectrum, Atari... all used Chips from this family (sometimes the YM variant instead of AY...)
As a result it is still quite popular in the actual Chip Tuning movement as a vintage sound processor.
Many Chip Tuning sites include AY files and scene.
Halas, the ZX Spectrum is more often used as reference. But a huge library is available
Technical references
Amstrad Plus specificity
The Amstrad Plus range include DMA sound channels. This offer extra capabilities, and extra bugs too...