[linux-audio-user] midi timing problems

James Stone stone1 at btinternet.com
Tue Nov 18 17:32:01 EST 2003

On Sat, Nov 15, 2003 at 05:12:45PM +0000, James Stone wrote:
> On Tue, Nov 11, 2003 at 09:13:58PM +0000, James Stone wrote:
> > Hello everyone.
> > 
> > I have a problem with midi timing.. I think I have set up enhanced rtc
> > correctly and low latency patch on kernel 2.4.20.
> > 
> > When I drive hydrogen (or even the inbuilt soundfont player on my
> > SBLive) with seq24 or ardour, there is a noticable variation in midi
> > timing. This was tested by using a run of closed hihats. When I play the
> > sequence back, the hihats are grouped in batches rather than being
> > evenly spaced. This was noticable when running as root and when using
> > alsa and (to a lesser extent) jack. The midi connection is via alsa.
> > 
> > Any hints on what I should do?
> > 
> > James
> Just to reply to myself,
> I solved the problem:
> I needed to install the snd-rtctimer for alsa. This required a patch to
> the kernel RTC (patch included with ALSA but also needed a tweak. see:
> http://www.geocrawler.com/archives/3/12349/2001/7/0/6299315/
> )
> After that, snd-rtctimer built okay. Then I added the following to
> modules.conf:
> options snd-timer snd_timer_limit=2
> options snd-seq snd_seq_default_timer_resolution=2000 snd_seq_default_timer=1
> options snd-rtctimer rtctimer_freq=2048
> alias snd-timer-1 snd-rtctimer
> Now, midi timing is sorted (at least for muse when running as root so it
> can access the RTC.. seq24 doesn't seem to be quite there yet in my
> experience).

Just a further note.. Needed to apply the variable frequency kernel
scheduling patch and set the frequency to 1000Hz and now the timing
problem with seq24 is solved.


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