How to access the PSG via PPI
From CPCWiki - THE Amstrad CPC encyclopedia!
Programmable Sound Generator
The CPC uses the AY-3-8912 PSG. This chip features 3 square-waves channels, a noise generator and an enveloppe generator often used at high frequencies to make different sounds.
The same chip is used in the ZX Spectrum, the Atari ST, and some others.