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AU Lab and sidechain inputs
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AU Lab and sidechain inputs


  • Subject: AU Lab and sidechain inputs
  • From: Andrew Wason <email@hidden>
  • Date: Wed, 13 Jan 2010 17:43:38 -0500

I wrote an AudioUnit that supports a sidechain input. When I host it
in AU Lab, and choose "Edit Inputs..." from the popup to connect the
sidechain this all appears to work, but in my AudioUnit when pulling
the sidechain input it always returns silence (and sets
kAudioUnitRenderAction_OutputIsSilence)

I hacked up the CocoaAUHost sample so that it creates two
kAudioUnitSubType_AudioFilePlayer AUs and connects one to my AUs input
and one to the sidechain - and now my AU gets valid data on both
inputs. So I think my AU is OK.

I think I am misunderstanding how to use AU Lab, or how to properly
setup the aggregate device. I'm on a MacBook Pro so I created an
Aggregate device with my microphone and bultin output in MIDI Setup
and use that with AU Lab.

I have 3 tracks in AU Lab, "Audio 1" (aggregate device input),
"Generator 1" (file player) and "Output 1".

My AU effect is on the generator and the sidechain "Input Source" is
set to "Audio Input". So I think this should be routing the microphone
output to my sidechain element 1, and the generators output to my
effects element 0 input.

Is there some other way I should be configuring this?  Also, I don't
see any way to route other sound sources (e.g. generator output) into
a sidechain input - the sidechain editor only has options "None" or
"Audio Input".



Here is the dump of the AUGraph from AU Labs showing the nodes and connections:


# # # The Session Graph:
AudioUnitGraph 0x21F0000:
  Member Nodes:
	node 1: 'auou' 'ahal' 'appl', instance 0x810000 O I
	node 2: 'aumx' 'mxmx' 'appl', instance 0x810001 O I
	node 3: 'aumx' 'mxmx' 'appl', instance 0x810002 O I
	node 4: 'aumx' 'mxmx' 'appl', instance 0x810003 O I
	node 5: 'augn' 'afpl' 'appl', instance 0x810004 O I
	node 6: 'aumx' 'mxmx' 'appl', instance 0x810005 O I
	node 7: 'aufx' 'Duck' 'MBau', instance 0x810006 O I
  Connections:
	node   4 bus   0 => node   3 bus   0  [2 ch, 44100 Hz]
	node   3 bus   0 => node   2 bus   0  [2 ch, 44100 Hz]
	node   2 bus   0 => node   1 bus   0  [2 ch, 44100 Hz]
	node   5 bus   0 => node   7 bus   0  [2 ch, 44100 Hz]
	node   7 bus   0 => node   4 bus   1  [2 ch, 44100 Hz]
	node   6 bus   0 => node   4 bus   0  [2 ch, 44100 Hz]
	node   6 bus   1 => node   7 bus   1  [2 ch, 44100 Hz]
	node   1 bus   1 => node   6 bus   0  [2 ch, 44100 Hz]
  CurrentState:
	mLastUpdateError=0, eventsToProcess=F, isRunning=T



This is the input manager section of the graph dump, the IsActive=0 on
the second output element looks suspicious (because this is what is
connected to my effects sidechain, and it appears to be disabled or
something?):


# # #  Input Managers
# # AudioInputManager:0x100379900
AudioUnit:0x810005
	node=6	CAComponent: 0x646f626967737304, AudioComponentDescription:
'aumx' - 'mxmx' - 'appl', 0x10000000, 0x10065
	1 Connections to this unit:
	    from [AUNode:1, elID=1] to [elID=0] :
		AudioStreamBasicDescription:  2 ch,  44100 Hz, 'lpcm' (0x00000029)
32-bit little-endian float, deinterleaved
	Input Channels = 2, Output Channels = 4
	Input Elements:
		0:[2, T]
	Output Elements:
		0:[2, T]  1:{2, F}
	Global Volume: 1.000
	1.000   (1.000) (0.000) (1.000) (0.000)
	1.000   (0.000) (1.000) (0.000) (1.000)
	         1.000   1.000   1.000   1.000
Input AudioDevice:
	Audio Sources: 2, wants input: T
	Using 2 Num Channels. Using Channels:
		[0:2] [1:2] [2:0] [3:0] [4:0] [5:0] [6:0] [7:0]
	  Element:0 CAEAudioSource:0x100372620, SrcBus=0, IsActive=1,
Starting Channel:0, Num Channels:2, Num Tracks:1
	  Element:1 CAEAudioSource:0x100578d80, SrcBus=1, IsActive=0,
Starting Channel:0, Num Channels:2, Num Tracks:0



Andrew
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