Re: . Re: Aggregate devices and clock domains question
Re: . Re: Aggregate devices and clock domains question
- Subject: Re: . Re: Aggregate devices and clock domains question
- From: Jeff Moore <email@hidden>
- Date: Tue, 17 Nov 2009 09:45:29 -0800
On Nov 17, 2009, at 9:15 AM, Stéphane Letz wrote:
>>
>>
>> Message: 14
>> Date: Tue, 17 Nov 2009 08:51:56 -0800
>> From: Jeff Moore <email@hidden>
>> Subject: Re: Aggregate devices and clock domains question
>> To: CoreAudio API <email@hidden>
>> Message-ID: <email@hidden>
>> Content-Type: text/plain; charset=iso-8859-1
>>
>> That's something for the drivers involved to figure out. To be sure in some cases, it's hard or impossible to do because the device itself doesn't know enough about the situation, so the driver can't really do anything. There are other cases though, where it does work out and the drivers can provide the specific information necessary.
>>
>>
>
> So what would happen if devices are effectively synched but clock domain property does not report that fact correctly? What would setting "clock drift compensation" do in this case?
>
> I hope it does nothing so that we can activate "clock drift compensation" in *all* cases where clock domain is not the same for all devices, and it would not harm if devices are hardware synched.
>
> Can we do that safely?
Absolutely not. Even two devices that are synchronized in hardware will have some small discrepancies in their time stamps that will look to the HAL as if they are drifting against one another. If the discrepancies are large enough, the drift correction will end up putting the devices out of sync.
This is one of the reasons why I said previously that it is important to offer the user the ability to to tell you which devices are synchronized and which ones aren't as a back-stop to using the clock domain property.
--
Jeff Moore
Core Audio
Apple
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