It was indeed better than the [[AY]] used in many other computers of the era (Amstrad's too) because it could produce many different (3) wave signal while AY could only produce rectangular wave signals.
Make your own judgment: [https://youtu.be/_LWbnjvXN4g YM AY vs SID sound comparison]
"SID" refers to a SIDfile, *.SID, too. Now playable -with some less quality- on CPC with Geco's Player. [http://www.hvsc.c64.org/ SID Resource site.]