I installed Ardour 6 and it seems the maximum buffer size supported for the Alsa backend has gone down? The drop-down menu of Audio/Midi setup has changed in terms of its range?
Moreover, this seems to have caused problems for running the older Ardour 5 variants on the very same machines. I can’t think what has polluted them. Possibly it’s a software automatic upgrade and nothing to do with changing Ardour versions. I’ve tried two machines, and four different USB audio devices (Fedora 31).
My real problem is that I was constantly getting the ‘cannot start audio … possibly hw_params’ dialog pop up, which is not very informative. This is at 44.1 for 16 to 20 channel interfaces. To assist, I recompiled Ardour and passed in the debug=1 flag in the last arg to the constructor of Alsa_pcmi. This then gives more revealing information about why it won’t start, saying on the stdout
Alsa_pcmi: can’t set capture period size to 1024
Alsa_pcmi: can’t set capture period size to 512.
when I select those sizes
It does not complain at all for 128 and 256 samples, but it does not start. I will dig further to see why.
For 64 samples, the driver starts ok but bombs out (ALSA I/O error dialog) within the minute or so, correlated with CPU activity on other application programs (I am not using the performance governor for these tests since I want to test my margins). Using the larger buffer sizes would obviously be much more tolerant to inter-process crosstalk, which is why I normally used them (along with hardware foldback and monitoring).
Why do you think the larger buffer sizes are no longer working for me? I’ve not made any system changes as far as I know. I’ll keep on exploring. It’s something to do with the alsa snd_pcm_hw_params_get_period_size
(I must say, it would be helpful to get the informative messages from the backend without having to recompile it. I’ll probably implement a private enabling backdoor from now on (using getenv or something)).
Many thanks - DJ Greaves