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Re: Slow audio device starting on Lion?
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Re: Slow audio device starting on Lion?


  • Subject: Re: Slow audio device starting on Lion?
  • From: Jeff Johnson <email@hidden>
  • Date: Tue, 24 Jan 2012 11:29:35 -0600

I had the opportunity to test with both 10.6 and 10.7 on a machine with up to 1/3 of a second latency. It looks like you're right about sync vs. async: while the total time was about the same, it spent most of the time blocking in AudioDeviceStart() on 10.6 but spent most of the time waiting for the callback on 10.7. Previously, I hadn't been able to test both 10.6 and 10.7 with the same machine.

It does seem to be very dependent on hardware. On the machine in question, I was consistently (though not constantly) getting 1/3 second, while on other machines I've seen as much as 1/2 second or as little as near 0 latency.

-Jeff


On Jan 22, 2012, at 10:46 AM, Dave Fernandes wrote:

> Interesting. I just looked at the issue again, and now AudioOutputUnitStart() doesn't block. I guess it changed from a synchronous function to an asynchronous one in Lion. But, like you, I still get the delay before data buffers start flowing.
>
> It's also interesting that you don't see this problem in Snow Leopard, but it's possible that we are testing on different hardware and that the hardware support for this "feature" is different on Lion and Snow Leopard.
>
> Dave
>
> On 2012-01-21, at 3:22 PM, Jeff Johnson wrote:
>
>> Hi Dave.
>>
>> It's been a while, but just following up.
>>
>> I'm not sure this is the same issue you were experiencing. Mine only started on 10.7, not on 10.6. Also, AudioDeviceStart() is not blocking, it returns immediately. The delay is just in the time it takes for the callback to first occur.
>>
>> -Jeff
>>
>>
>> On Jan 2, 2012, at 2:11 PM, Dave Fernandes wrote:
>>
>>> Sounds like a known problem on both Mac OS and iOS:
>>>
>>> http://lists.apple.com/archives/coreaudio-api/2010/Jun/msg00308.html
>>> http://osdir.com/ml/coreaudio-api/2011-01/msg00043.html
>>>
>>> Perhaps it is a power-saving feature, as Shaun Guth suggests.
>>>
>>> Dave
>>>
>>> On 2012-01-02, at 1:49 PM, Jeff Johnson wrote:
>>>
>>>> I'm calling AudioDeviceCreateIOProcID() and then AudioDeviceStart(). In my tests, I'm using the built-in output device. On some (but not all) machines running Lion, I'm seeing a half a second delay between the time AudioDeviceStart() returns and my AudioDeviceIOProc first gets called. I've never seen nearly this long of a delay with Snow Leopard and earlier. What would cause the delay, and is it to  be expected? I know that Core Audio has changed fundamentally in Lion, so I'm wondering if that has something to do with it.
>>>>
>>>> -Jeff


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References: 
 >Slow audio device starting on Lion? (From: Jeff Johnson <email@hidden>)
 >Re: Slow audio device starting on Lion? (From: Dave Fernandes <email@hidden>)
 >Re: Slow audio device starting on Lion? (From: Jeff Johnson <email@hidden>)
 >Re: Slow audio device starting on Lion? (From: Dave Fernandes <email@hidden>)

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