After slavering over cTrix's vectrex videos to the point of obsession, I'd like to put some effort into actually learning how to make tunes on the AY, even if it's only emulated. In fact, I'd prefer to mess about with it in emulation before buying anything. Can anybody suggest decent software to get started with? Linux compatibility is a big plus for me, but not strictly necessary.

The most user friendly software you can use is "Vortex Tracker II" : https://www.youtube.com/watch?v=x_36Rixs9eo
It works well with Wine on Linux.

There is also Arkos Tracker for windows. It works with Wine but require some tricks to make it work correctly: https://www.youtube.com/watch?v=9hJWGk5meIk
(btw listen to this wonder: https://www.youtube.com/watch?v=8C8DmOL6l_A )

There are also a couple of cool native software you can use with Atari ST emulators, like MaxYMiser or Defmon (they won't create AY or YM files, but SNDH which are tied to the atari st capacities)

You can have a look at my trackers comparison chart: http://garvalf.online.fr/index.php?page … s_trackers

+1 for the ST the YM2149 is technically a AY soundchip. Musicmon 2.5e, MaxYMiser and TripleX are good trackers on this computer !