After a little further investigation, I found that timidity was being started by systemd by falling back to /etc/rc*.d/ SYSV files.
Note that I had removed timidity-daemon, but I did not purge the package. As a result, it seems that timidity was being started: # systemctl list-units "timidity*" UNIT LOAD ACTIVE SUB DESCRIPTION timidity.service loaded active running LSB: start and stop timidity So if you have had timidity-daemon installed at some point, then be sure to purge the package. I see that timidity "Suggests" timidity-daemon, although it is not needed in desktop installations. I imagine that it how it got installed here some years ago. The other issue is why timidity is locking out other sound applications from using plughw:. Perhaps that would be reasonable when timidity is actively playing sound, although I think most sound aplications are not so antisocial. I have not looked at that aspect so far.
