Re: [linux-audio-dev] a question re: the MIDI spec

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Subject: Re: [linux-audio-dev] a question re: the MIDI spec
From: Martijn Sipkema (msipkema_AT_sipkema-digital.com)
Date: Sat Sep 11 2004 - 14:13:12 EEST


> > [...]
> > > > > > The problem here is that class compliant devices suffer bad timing
> > > > > > because they use bulk transfers for MIDI data. The standard for
> > > > > > MIDI over FireWire is much better.
> > [...]
> > > > > Is the timing really that bad? I don't even think a firewire 8x8
> > > > > rackmount MIDI interface exists, so my options are kinda limited. :/
> > > >
> > > > Timing is especially bad when there is other data being transferred on
> > >
> > > "Especially bad" is still pretty vague. What might look bad on paper might be
> > > acceptable in context...
> >
> > It's not unusable, but IIRC it can get to several ms of jitter.
>
> Why is that? The USB iso clock is every ms IIRC, so naively you
> would expect the maximum jitter to be just under 1ms (if the bus was
> saturated by audio transfers), and less in proportion to the degree of
> saturation.

Yes, one would expect that (if there are no other bulk transfers), but
somehow this does not seem to be the case:

http://www-2.cs.cmu.edu/~eli/papers/icmc01-midiwave.pdf

--ms


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