Re: synchronization of input and output
Re: synchronization of input and output
- Subject: Re: synchronization of input and output
- From: Taylor Holliday <email@hidden>
- Date: Fri, 30 Oct 2009 10:49:09 -0700
Thanks Jeff,
I'm actually currently using PortAudio, which on each processing
callback provides an inputBufferAdcTime and an outputBufferDacTime. So
as you said, I can just subtract those two quantities to determine the
shift of an input sample relative to an output sample. The difference
must be constant across consecutive callbacks, right?
My original motivation for asking is that I'm encountering a problem
in Logic where everything is recorded slightly (audibly) late, so I'm
wondering where the correlation is breaking down. This was when using
an aggregate device to link two audio interfaces together. But also,
at home with my apogee duet I did a loopback test and saw that
everything was recorded 10 samples or so late. So I'm wondering why
neither setup is precisely synchronized.
- Taylor
On Thu, Oct 29, 2009 at 3:09 PM, Jeff Moore <email@hidden> wrote:
> Correlating the time of the input and the time of the output is done using
> the time stamps that are provided by the various APIs. They provide a time
> stamp for when the input data was acquired as well as a time stamp for when
> the output data is going to hit the wire. Both time stamps are from the same
> time line, so they are already correlated and you can just subtract to get
> the number of sample between them.
>
> At any rate, it would help to know what API you are using and probably a bit
> more about what you are trying to do to provide any more specific help.
>
>
> On Oct 29, 2009, at 3:00 PM, Taylor Holliday wrote:
>
>> How does a CoreAudio recording app ensure that newly recorded
>> material (i.e. an overdub) is sample-synchronized with previously
>> recorded material? Or more specifically: when recording how might one
>> determine to which output sample a given input sample corresponds?
>
>
> --
>
> Jeff Moore
> Core Audio
> Apple
>
>
>
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