[timidity-talk] Out of sync playback with ALSA sequencer on Debian

[Bill C. <bil...@ou...>]

Hi,

First of all I would like to thank you guys for creating this great piece of software, and handing it out for free!  However, I have issues with playing back midi files with TiMidity++ on Debian Wheezy/Jessy.
If I play the files without using the ALSA server:
timidity -Os filename.mid
the playback is fine.  If I play the files with the ALSA server:
aplaymidi -p 128:0 filename.mid
there is a lot of jitter and the notes are out of sync.  This happens both with aplaymidi as with other applications (e.g. games running in dosbox and wine).

I've tried to resolve the problem myself, without success:
- I tried different soundfonts (both the default one and external ones)
- I tried to lower the sampling frequency (which is noticeable in quality, but the jitter is still present)
- I tried all available ports
- The Arch wiki says that running TiMidity++ with the libao backend may solve such issues, but this backend is not compiled in the binaries of the debian repos.  I therefore compiled timidity myself with this backend.  The sound is not out of sync this time, but it stutters :(  With the libao "verbose" option, I get these warnings: “ao_alsa debug: underrun, restarting...” (changing the buffer_time value does not help)

If I change the backend of the TiMidity++ server to "output to file" (option -Ow), the resulting file does not contain any jitter or stuttering at all.  Clearly there must be something wrong with the ALSA backend, but where should I look?
(I don't use Pulse, as TiMidity++ has no native PulseAudio support)

To illustrate the problem, I recorded samples with the snd_aloop loopback module:

- Playback to file, as it should sound ( -Ow ):
http://a.pomf.se/iawwsh.mp3

- Playback to alsa sequencer with alsa, out of sync ( -Os ):
http://a.pomf.se/lbtdpu.mp3

- Playback to alsa sequencer with libao, stuttering ( -OO ):
http://a.pomf.se/djbipx.mp3

I am really desperate at this point: any hints would be welcome!

Kind regards,

Bill Carson