Re: [Alsa-user] midi timing issues (?) with m-audio delta-44, f8, ccrma distro

[stan <ghj...@co...>]

steve linabery wrote:
> If I import a known good midi file into Rosegarden, for example, and
> send the midi to my vDrum brain, it sounds like it's being played by
> someone with no sense of rhythm.
> 
> Yesterday I recorded a performance using both ardour and rosegarden
> (capturing audio and midi, respectively), then re-recorded audio using
> the midi recording and my vDrum as a sound source, and the resulting
> audio tracks were more or less spot-on the same.

Indicates the problem isn't ALSA but as you suggest below, a 
timing/interrupt issue.

> 
> Today, I did the same thing, and I got the "absolute beginner" effect
> described in paragraph 1 above.

Could you run top and iotop while you are doing this.  It is possible 
that there is something that is running in the background that has a 
higher priority than your application, and is thus causing timing errors.

> 
> I don't really understand how to debug the timing source on my system.
> I'm running the ccrma distro, so I assume the kernel has high
> resolution timing compiled in.

I don't either. ;-)  When I looked at CCRMA, it seemed your statement 
is true.  Did you modify the file as described here from CCRMA
http://ccrma.stanford.edu/planetccrma/software/installfedoraseven.html#SECTION00040600000000000000
...
If this is an update, that is, you have previously installed the 
jack-audio-connection-kit that is part of the Fedora repository, you 
will need to edit /etc/security/limits.conf to modify the permissions 
for realtime scheduling and memory locking (which are set by the 
Fedora Jack package to much more conservative values than what Planet 
CCRMA needs).

So, edit /etc/security/limits.conf and see what you have for the 
values of ``rtprio'', ``nice'' and ``memlock'' parameters, if the 
lines where those parameters appear start with anything other than 
``*'' then you need to change the file. Change those lines to be:

* - rtprio 99
* - nice -10
* - memlock 4000000

(this will give any user access to realtime scheduling and memory 
locking - not just a group - and the maximum usable priority will be 
99 instead of - last time I checked - 20).
...

You could look at man getrlimit and man setrlimit as well.

Note that this could have security and performance ramifications.  You 
could instead create an audio group, add yourself to it, and give the 
above settings to it.

@audio - rtprio 99
etc.

Also note that this advice is not repeated for Fedora 8, though there 
is no explanation.

> 
> Here's the output from alsa-info:
> http://www.alsa-project.org/db/?f=daa5d493389103b81ab071e81c3bfba1b19f803d
> 
> I think I'll try a more recent kernel and see if that helps. I use
> 2.6.24.7-1.rt3.2.fc8.ccrmart at the moment because when I first
> installed f8/planetccrma the most recent kernels gave me some system
> hangups.
I don't think this will help, but worth a try.
> 
> Thanks for any advice/info.
> 
> Good day,
> Steve