User:Jeff Kelley/Multichannel Audio

   WORK IN PROGRESS

Introduction

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:

Step 2: Open with QuickTime Pro

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

Step 3: Export to QuickTime Movie

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

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.

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.

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 http://www.ambiophonics.org/AESJune2003/AES_June_2003_1.htm

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
SMPTE/ITU	6	L R C LFE Ls Rs
DTS	6	L R Ls Rs C 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)