Re: Odd things with MOTU 828mkII
Re: Odd things with MOTU 828mkII
- Subject: Re: Odd things with MOTU 828mkII
- From: Jeff Moore <email@hidden>
- Date: Wed, 5 May 2004 14:31:42 -0700
On May 5, 2004, at 12:50 PM, Robert Grant wrote:
I've got a user with a MOTU 828mkII who's having trouble with ReVision.
It seems that the 828 expects an app to set the sample rate before
sending data.
As far as I know, this isn't the case.
I don't do this because I ask for the sample rate of the
DefaultOutputUnit and work with that. This seems to work with most
systems but on the 828 this only works if the last sample rate used is
48kHz. Then ReVision picks up the 48kHz and everything plays
correctly.
Starting with Panther (and systems with QT 6.4 or later installed), the
HAL saves each audio device's current format and then restores it at
boot. So under most user's circumstances, the HAL has long since
already told the hardware what sample rate to use.
However if the last sample rate sent to the 828 is 44.1kHz and
ReVision plays at this rate the audio comes out about a tone too low.
It's like the 828 is saying that it expects the audio in 44.1 but then
actually pulls at a different rate.
To add to the weirdness the video plays back at a different rate too
but perhaps QuickTime is getting it's timing from the
DefaultOutputUnit too?
It sounds like the user reporting the problem has the 828 slaved to an
external clock. Thus, it could report that it is running at 48K, but
because the clock it is synchronized to is running at 44.1, it runs
slow. You should check to be sure that the clock source control in AMS
says that the 828 is using internal synch or that the master device is
really running at the sample rate you think it is.
--
Jeff Moore
Core Audio
Apple
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