Re: channel layout for 3DMixer
Re: channel layout for 3DMixer
- Subject: Re: channel layout for 3DMixer
- From: William Stewart <email@hidden>
- Date: Wed, 28 Oct 2009 11:50:42 -0700
the 3D mixer does not provide LFE data
I good tool to run an audio units to see what they do is the auval
tool. The relevant part of the 3DMixer looks like this:
% auval -v aumx 3dmx appl
...
FORMAT TESTS:
Reported Channel Capabilities (explicit):
[1, 2] [2, 2] [4, 2] [1, 4] [2, 4] [4, 4] [1, 5] [2, 5]
[4, 5] [1, 6] [2, 6] [4, 6]
[1, 7] [2, 7] [4, 7] [1, 8] [2, 8] [4, 8]
...
# # AudioChannelLayouts (3), Input Scope:
ChannelLayout is Writable: F
The Unit publishes the following Channel Layouts:
0x640001, 0x650002, 0x6B0004,
# # AudioChannelLayouts (7), Output Scope:
ChannelLayout is Writable: F
The Unit publishes the following Channel Layouts:
0x650002, 0x6C0004, 0x760005, 0x8B0006, 0x8C0007, 0x940007, 0x6F0008,
You can see from this that there are 2 7 channel formats supported
(7.1 rear, 7.1 front) - you can choose from these, but otherwise your
layout would be rejected.
You can and should, handle LFE differently I think, and if you want to
generate an LFE channel (rather than have your stereo system provide
low frequency data to the sub through bass management, which is a
common way for this to be resolved), would be to use a multichannel
mixer and have the 7 channel input going in as the first input and a
mono input as the second - this is your LFE channel and you can derive
that however you want. Then the output of the multichannel mixer would
be 8 channels, which you then connect to the device for output
% auval -v aumx mcmx appl
...
Reported Channel Capabilities (explicit):
[-1, -2]
# # AudioChannelLayouts (1), Input Scope:
ChannelLayout is Writable: T
The Unit publishes the following Channel Layouts:
0x0 (Use_Channel_Descriptions)
# # AudioChannelLayouts (1), Output Scope:
ChannelLayout is Writable: T
The Unit publishes the following Channel Layouts:
0x0 (Use_Channel_Descriptions)
(What this means is that the multichannel mixer can handle any channel
orders or numbers on input and output, so you can route this any way
you like)
Bill
On Oct 28, 2009, at 5:27 AM, Antoine Gonot wrote:
Dear list,
When I set the number of channel for the 3DMixer output stream
format, the channel layout tag is automaticaly set to the folowing :
numChannel = 5 -> kAudioChannelLayoutTag_AudioUnit_5_0
numChannel = 6 -> kAudioChannelLayoutTag_AudioUnit_6_0
numChannel = 7 -> kAudioChannelLayoutTag_AudioUnit_7_0
etc.
I would like to change this, in order to have a channel dedicated to
the LFE (this is requiered by my 5.1 amplifier !). However, each
time I try to change the channel layout tag, the
AudioUnitSetProperty function return me an error, even if I respect
the number of channel. For exemple, I tried to set the tag to
kAudioChannelLayoutTag_AudioUnit_5_1 with 6 channels output stream
format. Its seems that the 3DMixer does not allow to change speaker
configuration. Is there any method to achieve this ?
best regards,
Antoine Gonot
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