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Experimenting with kAudioDevicePropertyIOCycleUsage

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Experimenting with kAudioDevicePropertyIOCycleUsage

Subject: Experimenting with kAudioDevicePropertyIOCycleUsage
From: Stéphane Letz <email@hidden>
Date: Wed, 5 Mar 2008 15:49:49 +0100

Hi,

We are experimenting the use of kAudioDevicePropertyIOCycleUsage property to reduce the output latency (and thus the overall I/O latency) of our application. Since the real audio process is somewhat decoupled from the audio IO callback, we know for sure that what is actually done in the CoreAudio audio IO callback is fast and time bounded : that is read input buffers, and write output buffers from already computed buffers in memory.

When experimenting with a kAudioDevicePropertyIOCycleUsage of 0.5 on a PowerBook G4 with the built-in device and 128 frames we see kAudioDevicePropertyIOCycleUsage coming even when the IO CoreAudio callback actually just returns immediately. Since the available time should be 64 frames (= 1.45 ms at 44 kHz), the observed behaviour seems incorrect.

The problem can actually be reproduced using Apple AULab and playing with the "Preferences/Devices/Expert Settings/CPU Usage for Audio Processing"

Are they any special conditions to follow when using this kAudioDevicePropertyIOCycleUsage property?

Thanks

Stephane Letz _______________________________________________ Do not post admin requests to the list. They will be ignored. Coreaudio-api mailing list (email@hidden) Help/Unsubscribe/Update your Subscription: This email sent to email@hidden Follow-Ups: Re: Experimenting with kAudioDevicePropertyIOCycleUsage From: Jeff Moore <email@hidden> Prev by Date: Re: Is a CoreAudio bug the cause of the annoying "overload" messages in Logic 8 ? Next by Date: Re: Is a CoreAudio bug the cause of the annoying "overload" messages in Logic 8 ? Previous by thread: Re: CASpectralProcessor and general 64 bit SDK compatibility Next by thread: Re: Experimenting with kAudioDevicePropertyIOCycleUsage Index(es): Date Thread