Re: USB Audio 1ms gaps
Re: USB Audio 1ms gaps
- Subject: Re: USB Audio 1ms gaps
- From: Brian Willoughby <email@hidden>
- Date: Thu, 15 Sep 2011 03:15:33 -0700
On Sep 15, 2011, at 02:55, Vyacheslav Matyushin wrote:
I'm developing a driver for USB Audio board.
On low sample rates the stream is quiet stable, but on high rates
(192kHz and higher) I see gaps of 1 ms.
(So they practically never appear at 44.1kHz and almost always are
at 384kHz).
They can appear once per several seconds or a few times per second.
The data gets to stream buffers without gaps.
Gaps of 2 and 3 ms also appear but much more rare.
If the stream buffers from which convertInputSamples() takes data
have no gaps
where do gaps appear from?
Are you aware that USB has a frame rate of 1 ms? If you want to pull
data out at a constant rate, you'll need to design for a latency of 1
ms or on power of 2 multiples, buffer the incoming, jittery data to
smooth it out to a regular rate. You also need to queue up your
requests plenty of time in advance, otherwise you could miss some
frames.
Have you considered Apple's USB Mailing List? It may more quite a
bit more appropriate for your questions than the CoreAudio Mailing List.
Brian Willoughby
Sound Consulting
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