Re: multichannel device with ahal
Re: multichannel device with ahal
- Subject: Re: multichannel device with ahal
- From: Doug Wyatt <email@hidden>
- Date: Tue, 23 May 2006 17:25:00 -0700
On May 23, 2006, at 16:02 , Christoph Teschner wrote:
I use an AUGraph with the ahal unit as the output. The output is
connected to a matrix mixer with one output bus consisting of 4
channels.
OK ... you are providing 4 channels from a matrix mixer connected to
the output unit ...
When using the ahal without any further settings it runs with the
default output from the AudioMidi Setup. If a multichannel output
device is selected there the output plays the 4 channels of the
matrix mixer.
But when I programmatically set
kAudioOutputUnitProperty_CurrentDevice of the ahal to the same
multichannel device only the first two channels of the same device
are used.
Any help about what I'm missing would be appreciated.
Have you set a channel layout on the output unit's bus 0 (output)
input scope? (this layout should correspond to your render format, 4
channels)
It's been some time since I've been in this code, but it looks like
when you make a connection from the matrix mixer to the output unit,
no channel layout is getting set on the output unit's bus 0/input
scope. With no channel layout there, AUHAL doesn't look like it
should be doing any additional remapping.
One possibility is that sometimes AUHAL is using an incorrect default
channel map where only the first two channels go anywhere, and in
other situations, a correct 4-channel-pass-through channel map is
being applied.
Another possibility is that you are making the connection from the
matrix mixer to the output unit at a time when the matrix mixer still
has a default (stereo) output format. Try this:
AudioStreamBasicDescription auHalSourceFormat;
UInt32 size = sizeof(auHalSourceFormat);
OSStatus err = AudioUnitGetProperty(myAuHalInstance,
kAudioUnitProperty_StreamFormat,
kAudioUnitScope_Input, 0, &auHalSourceFormat, &size);
What is auHalSourceFormat.mChannelsPerFrame ?
Thanks
Doug
--
Doug Wyatt
Core Audio, Apple
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