Re: 3D Mixer Equal Power Panning - Follow up on panning
Re: 3D Mixer Equal Power Panning - Follow up on panning
- Subject: Re: 3D Mixer Equal Power Panning - Follow up on panning
- From: James McCartney <email@hidden>
- Date: Tue, 17 Apr 2007 11:29:09 -0700
On Apr 17, 2007, at 11:05 AM, William Stewart wrote:
We'll look into it - BTW, it would probably be quite simple to add
this to CAF files (we already have some tags, etc for ambisonic
channels)
CAF and AIFF files already support this for 3 or 4 channel B format.
There is a channel layout tag for 4 channels, so that is easy. Just
put the B format channels in the file in WXYZ order and set the
channel layout to:
kAudioChannelLayoutTag_Ambisonic_B_Format
defined in CoreAudioTypes.h
AudioFileID afid;
...
AudioChannelLayout acl;
memset(&acl, 0, sizeof(acl));
acl.mChannelLayoutTag = kAudioChannelLayoutTag_Ambisonic_B_Format;
UInt32 propertySize = sizeof(acl);
OSStatus err = AudioFileSetProperty(afid,
kAudioFilePropertyChannelLayout, propertySize, &acl);
We could add a tag for 3 channel B format. However you can also do
that already:
AudioFileID afid;
...
AudioChannelLayout *acl = (AudioChannelLayout*)calloc(1, sizeof
(AudioChannelLayout) + 2 * sizeof(AudioChannelDescription));
acl->mChannelLayoutTag = kAudioChannelLayoutTag_UseChannelDescriptions;
acl->mNumberChannelDescriptions = 3;
acl->mChannelDescriptions[0].mChannelLabel =
kAudioChannelLabel_Ambisonic_W;
acl->mChannelDescriptions[1].mChannelLabel =
kAudioChannelLabel_Ambisonic_X;
acl->mChannelDescriptions[2].mChannelLabel =
kAudioChannelLabel_Ambisonic_Y;
UInt32 propertySize = sizeof(acl);
OSStatus err = AudioFileSetProperty(afid,
kAudioFilePropertyChannelLayout, propertySize, acl);
free(acl);
The bit field in WAVE headers does not provide bits for these channel
labels, so you can't set these layouts currently on WAVE files.
On 17/04/2007, at 7:45 AM, Shawn Erickson wrote:
On Apr 17, 2007, at 4:35 AM, Richard Dobson wrote:
William Stewart wrote:
glad to hear.
As for the stereo pass through - its just defined for stereo at
the moment. The mixer's inputs are either mono or stereo
(except that we will also take a 4 channel WXYZ stream
(kAudioChannelLayoutTag_Ambisonic_B_Format) and decode it to
the current output layout)
A poropos of which: might Apple consider adding support for the
new WAVE_EX-based B-Format file format (.amb), defined here:
http://www.ambisonic.net/fileformats.html
to Quicktime etc? It does support higher orders, but having
basic support for 3 and 4ch 1st-order (WXY(Z)) files would be
enough to get started with!
Consider filing an enhancement request with Apple (this list isn't
really an official channel for such requests)...
<http://developer.apple.com/bugreporter/>
-Shawn
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