Re: Two AUHALs, one ring buffer, and one AU filter. But no sound.
Re: Two AUHALs, one ring buffer, and one AU filter. But no sound.
- Subject: Re: Two AUHALs, one ring buffer, and one AU filter. But no sound.
- From: Jeff Moore <email@hidden>
- Date: Thu, 1 Jul 2004 16:42:16 -0700
The reason you will get glitches is precisely what Robert said "The
syncing issue is that the two devices may be running at slightly
different actual sample rates". In other words, the differences between
the clocks of the two devices will eventually cause the output device
to be far enough ahead or behind of the input device that a sample gets
dropped (ahead) or a sample needs to be added (behind). This will
manifest as a little hiccup or glitch when you listen to the output.
In order to keep this from happening, you need to resample one device's
data to match the rate scalar of the other device.
On Jul 1, 2004, at 4:19 PM, john wrote:
Hi Chilton,
What Robert suggested is good. Though I'm not sure why he says you'll
eventually get audio glitches (can you answer Robert?).
I use a similar method - using MTCoreAudio's MTByteBuffer I grab data
from the input proc, do stuff with it, then when the AudioUnit output
calls back I just return to it the amount of data it wants. I never
have any audio glitches (at least that I notice).
-- John
Hi Chilton,
What you're trying to do is not impossible. You can pass the audio
from the input device (the iMic) through your buffer to the output
device. The syncing issue is that the two devices may be running at
slightly different actual sample rates - even though they're both set
to 44.1 kHz (for example) - meaning that you're eventually going to
get subtle audio glitches.
It sounds like you need to build things bit by bit:
Get input working with your render proc
Then start putting it in the ring buffer.
Then start pulling from the buffer using the render callback from
your Output Unit.
Then insert your filter.
Trying to do it all in one go seems to be adding confusion...?
Best,
Robert.
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--
Jeff Moore
Core Audio
Apple
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