Re: Multiple HALAOUs don't get along?
Re: Multiple HALAOUs don't get along?
- Subject: Re: Multiple HALAOUs don't get along?
- From: Robert Grant <email@hidden>
- Date: Wed, 16 Jun 2004 14:19:16 -0400
In Rax I decided to always create a second AUHAL unit for handling
input whether the device needed it or not - to avoid having the special
USB case. This seems to work well but does mean I have to glue it into
the graph - but I was doing that anyway for instruments.
The issue with handling mulitple devices is clock drift. Perhaps this
is also something that Apple will be providing a neat solution for...?
Certainly it is a standard problem that everyone wanting multi-device
support would have to address.
Hopefully someone attending the conference will keep us updated as much
as they can?
Robert.
On Jun 16, 2004, at 1:53 PM, James Coker wrote:
You can only have one HAL output unit per AUGraph. That component
can do both input and output, but not with USB devices. Due to the
way the USB audio spec works, USB audio interfaces appear as 2 devices
to Core Audio,
one for input, one for output. So in addition to your AUGraph with
your
FX and HAL output unit, you need to have another HAL Output Unit
running by it self (not in the AUGraph) that collects input and via
some callbacks, passes data to the first effect in your AUGraph.
It is all explained here:
http://developer.apple.com/technotes/tn2002/tn2091.html
There's been much discussion of this on the list, search
for postings with HAL Output Unit in the subject line.
Unfortunately, it is very not simple. However, as Bill Stewart has
recently hinted, there may be announcements at WWDC about
new CoreAudio features that may simplify things a bit.
Cheers,
Jim
On Jun 15, 2004, at 7:05 PM, Chilton Webb wrote:
Hi,
I wanted to use the HAL AudioOutputUnit to allow audio to pass
through a filter, to the output. However, Bill said that I can only
have one device per AU (currently). So I created two AUs, one for
input, and one for output. However, that doesn't work, for either
internal or external input (ie doesn't work at all).
So what is the simplest approach I can take to pass audio from a USB
mic, through a filter, and back out the speakers, in real time?
Thanks,
-Chilton
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