Re: AudioDeviceRead and timestamps
Re: AudioDeviceRead and timestamps
- Subject: Re: AudioDeviceRead and timestamps
- From: Andrew Kimpton <email@hidden>
- Date: Tue, 24 Jun 2003 22:18:37 -0700
Jeff Moore wrote:
The PlayEffect sample code uses AudioDeviceRead. You can consult that
code for a usage example.
I think that the root of your problem is that you aren't leaving
enough slop when calculating the input time. The reason why is that
the current time is already too late so you need to back off a bit
(determined by experimentation) before subtracting the safety offset
and the buffer size.
in response to my question :
On Thursday, June 19, 2003, at 5:04 PM, Andrew Kimpton wrote:
I'm using AudioDeviceRead() during an output callback to also read
the audio from the input device (this is USB Audio - so the input and
output devices are different).
I've setup my BufferList and everything just fine - I get audio into
my buffers without any problems. However there appears to be a +/- 1
sample 'wobble' in the acquired data.
Thanks to a quick chat with Jeff this afternoon at WWDC I appear to have
fixed my problem (I've not exhaustively tested it yet however, but for
30 - 90 seconds it sounds fine).
The fix basically was to remember that the two different devices (input
& output) are (or can be) running from different clocks, so you can't
reliably use the inNow time from the output device ioProc callback to
provide a time value for the input device AudioDeviceRead() call.
Instead the solution is to maintain my own count of sample position time
for the input device, and to initialize this on the first output device
ioProc callback and to then increment it by 'buffer size' samples on
each subsequent call. This seems to work fine and my wobbles have gone away.
Thanks for your help Jeff
Andrew 8-)
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