Re: Measuring Input/Output latencies
Re: Measuring Input/Output latencies
- Subject: Re: Measuring Input/Output latencies
- From: Stéphane Letz <email@hidden>
- Date: Thu, 25 Aug 2011 11:57:04 +0200
Le 25 août 2011 à 04:58, Ross Bencina a écrit :
> Hi Stéphane
>
>> 2) Measured latency differs from the driver reported latency, we were assuming that:
>>
>> Input latency = Input latency safety offset + Input latency + IO buffer size
>>
>> Output latency = IO buffer size + Output latency + Output latency safety offset
>>
>> So global IO latency would be : Input latency safety offset + Input latency + 2 * IO buffer size + Output latency + Output latency safety offset
>
> As Brian said, defining "input latency" as the sum of kAudioStreamPropertyLatency and kAudioDevicePropertyLatency the above formula is what we're currently using in PortAudio.
>
> We have noticed some discrepancies between actual and reported latency in our own testing but the PA loopback test is still under development.
>
>> But we see this reported "extra loopback latency".
>>
>> Does this value correspond to some additional ADC/DAC conversion latency?
>
> I wonder if there are other system level audio processing/SRC in place, and where the latency of these elements is reported.
>
> Thanks
>
> Ross.
Well according to this mail: http://lists.apple.com/archives/coreaudio-api/2008/Aug/msg00160.html
Latencies are supposed to change from stream to stream, in particular depending of Analog/Digital status:
But reading the stream latencies for : MacBook Pro (analog only), Mac Pro (analog/digital), Motu 828 Mk2 (analog/digital), I get 0 for all streams....
Stéphane Letz _______________________________________________
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