Have a look at:
which lists a bunch of European universities involved in sound and
music computing. There are also several universities doing music tech
stuff in Britain (Edinburgh, York, London, Plymouth...) and Ireland
(Belfast, Dublin, Limerick) which aren't mentioned there. [Plug:] I'm
in Uni of Limerick and there is a group here doing "interaction
design", often applied to music: http://www.idc.ul.ie/
Search scholar.google.com for the area you'd like to study (eg "audio
human computer interaction", and note the author and institution names
that appear on the papers!
It is sometimes possible to get funding for a PhD, eg through an EU
grant, and the best bet is to make contact with people you'd like to
work with and see what they say.