User:Jeff Kelley/Multichannel Audio

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Since QuickTime 7, it is possible to deliver multichannel audio. Second Life streamed audio relies on QuickTime and inherits this capability without further work.

Producing a multichannel audio movie

Step 1: Produce an interleaved multichannel WAV file

We are using ProTools. Bounce a multichannel session to Stereo interleaved format:

PT Multichannel Track.png

Step 2: Open with QuickTime Pro

Choose menu 'Show Movie Properties', select 'Sound Track', select 'Audio Settings' tab:

QT Audio Tracks Assign.png

Step 3: Export to QuickTime Movie

Choose 'Export', 'Movie to QuickTime Movie', 'Options', 'Sound Settings', 'Channels'.

QT Audio Tracks Export.png

Step 4: Stream the usual way

Using an HTTP server and Second Life's 'About Land > Media'.

Playing multichannel audio

In order to play multichannel audio, we need to link some audio hardware to QuickTime, don't we? On Windows, this is done in the QuickTime Settings control panel. First, select an audio interface (aka "sound card"), then select a mutichannel format.

QT Audio Tracks Interface Win.jpg

On the Macintosh, this is done via the Audio Midi Setup utility (not via the Sound control panel as one would expect). Select your multichannel interface in the Properties popup menu. Click Configure Speakers, then Multichannel.

QT Audio Tracks Interface Mac.png

Here, we are assigning the 8 analog output channels of our DIGI 002 studio interface to a 5.1 surround setup. The speakers setup must match stream content otherwise we would get "sound everywhere in the room" but no spatial location.

QuickTime multichannel audio support

Channels Assignements

L Left
R Right
C Center
LFE LFE Screen
Ls Left Surround
Rs Right Surround
Lc Left Center
Rc Right Center
Cs Center Surround
Rls Rear Surround Left
Rrs Rear Surround Right

For a full-reference, see QuickTime 7 Audio Enhancements

Note: Core Audio also support the following recording formats: XY Stereo, MS Stereo, WXYZ Ambisonic (B-Format). The latter is especially interesting for immersive 3D with soundfield recordings. Although consumer multichannel audio supports only surround formats, some succes has been achieved matrixing ambisonics to surround. See Robert Miller, AES 2003

Multichannel Mixing and Surround Formats

Format Channels Layout
Mono 1 C
Stereo 2 L R
Cinema Stereo 3 L C R
Quadraphonic 4 L R Lr Rr
Dolby ProLogic 4 L C R S
Film (Dolby Digital) 6 L C R Ls Rs LFE
Dolby Surround EX 7 L C R Ls Cs Rs LFE
SDDS 8 L Lc C Rc R Ls Rs LFE

NOTE: delete Image:Jef Kelley Images QT Audio Tracks Assign.png (stupid one)