Application Support of hardwareSampleRateChanged and external clocking
Application Support of hardwareSampleRateChanged and external clocking
- Subject: Application Support of hardwareSampleRateChanged and external clocking
- From: "David A. Hoatson" <email@hidden>
- Date: Mon, 31 Jan 2005 08:44:29 -0800
- Organization: Lynx Studio Technology, Inc.
Hello,
Our Core Audio driver calls hardwareSampleRateChanged() when it detects a
sample rate change from an external device (when clocking externally).
From our in-house testing application support for using this call is, at
best, limited. Some applications seem to notice that we called
hardwareSampleRateChanged (Nuendo, Cubase), but then don't do anything
useful with the information. Some applications (DP4 and Logic 7), will
simply hang when the external sample clock is changed, and it is 'Force
Quit' time. Obviously this is a serious problem for the end user as they
are used to pressing the sample rate button on their external converter...
Is there any other way to notify the application that the external clock
has changed, so it can do something useful with this information (such as
inform the user!)? Nuendo/Cubase with our Windows ASIO driver handle the
sampleRateDidChange() callback very nicely by popping up a dialog box
telling the user that the sample rate changed and what the new rate is. So
far, no OSX applications that we have tested do this.
I should also say that our Core Audio driver does look at the sample rate
of the external clock and will change the requested rate
(performFormatChange) to the rate of the external clock (and call
hardwareSampleRateChanged from within the performFormatChange handler). We
have noticed that sometimes this will cause the application to get caught
in an endless loop (when the app thinks it really has control over the
sample rate, and it doesn't).
Any ideas as to how to make this work more smoothly?
I would specifically like to hear from application developers as to what
they are expecting the hardware driver to do with respect to external
clocking.
Thank you,
David A. Hoatson
Lynx Studio Technology, Inc.
www.lynxstudio.com
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