Subject: Re: [linux-audio-dev] introduction & ideas
From: David Olofson (david_AT_gardena.net)
Date: Wed Mar 06 2002 - 05:28:20 EET
On Tuesday 05 March 2002 16.10, Paul Davis wrote:
[...]
> >Yeah... The stream frame rate is the clock.
>
> the window/macos worlds have been pretty unhappy with this
> arrangement, which i am convinced is part of the reason for the
> emergence of these newer interfaces which accept pre-queued
> data. timing MIDI with the audio clock just doesn't work well
> enough. even at the best typical resolution (1.3msec, or 64 frames
> at 48kHz), the MIDI sloppiness is something i've seen lots of
> complaints about on vst-plugins, for example.
Not surprising. Even 1.3 ms is worse than the old Win16 sequencers,
and you need a fast machine, a perfect configuration and luck to get
that kind of buffer size to work without (too many) drop-outs...
> granted, some
> interfaces can go lower than this, but its not clear its a good
> idea for the overall system.
It's not even clear it's *possible*, even if the interface can do it
in theory. (That may require a real OS! ;-)
> and besides, what we want, ideally, is
> a clock running at the MIDI rate.
Yeah - and then all we need is to read a common high resolution timer
(TSC) from whithin the MIDI and audio "engine loops", to get
*perfect* timing, down to the resolution of the respective
interfaces. :-)
(Of course, unless we use RTL or RTAI for the timestamping, we'd
still need some of those dreaded PLLs - but only to deal with the
occasional latency peak into the hundreds of µs range. It's probably
sufficient to assume that the average timestamp error is zero.)
//David
.- M A I A -------------------------------------------------.
| Multimedia Application Integration Architecture |
| A Free/Open Source Plugin API for Professional Multimedia |
`----------------------> http://www.linuxaudiodev.com/maia -'
.- David Olofson -------------------------------------------.
| Audio Hacker - Open Source Advocate - Singer - Songwriter |
`-------------------------------------> http://olofson.net -'
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