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The Third Annual Interactive Music Conference
PROJECT BAR-B-Q 1998
brainstorming graphic

Group Report: Making Sense Of Multi-Format Audio

Participants: Joe Forget; Interact Accessories
Dave Govett; Nemesys Bill Havlicek; Creative Labs
Michael Land; Lucas Arts Tony Padilla; Interact Accessories
Keith Weiner; DiamondWare Facilitator: Jeff Johannigman
 

The "Making Sense of Multi-Format Audio" group was formed to discuss the appropriate way for the audio subsystem to handle the mixing of multiple input formats to various output formats. We have addressed this non-trivial problem and prepared the following proposal:

  • At any given time, there may be many input formats in use, but only one output format.
  • The output format is selected by the user based on his/her speaker configura- tion. The channel format of the primary mix buffer is set to the same format as the selected speaker configuration.
  • Sound card outputs are discrete channels, either analog or digital, and in the same channel format as the primary mix buffer and speaker configuration, with one exception: the L,C,R,S speaker array implies a post mix encode to Dolby Pro Logic stereo.
  • At this time, it seems unlikely to use AC3 as an output format from the sound card due to the high cost of AC3 encoding.
  • We assume that the LFE channel is the only source for the subwoofer in discrete 5.1 systems.

A QUALITY PITFALL TO AVOID:

Mono 3D object ( 5.1 mix) virtualized to stereo speakers.

To see why this is bad, imagine a gunshot positioned directly behind the listener. Mixed to 5.1 it would be present equally in LS and RS. If this were then virtualized there would be a separate HRTF performed on each of the two instances and the two HRT's would interfere with each other.

The moral is that if the ultimate destination is stereo speakers, the main mix should be done to stereo. Users should be instructed that even if they have stereo speakers with virtual 5.1, they should still select stereo speakers as their output format. By extension, there is no role in interactive applications for virtualization within the speakers.

 

Making Sense of Multi-Format Audio: Audio I/O Format Matrix

Discrete N-ch
(7, 1, etc...)
TBD TBD TBD TBD TBD TBD
AC3
(DTS? SDDS?)
Decode
L,C,R,LFE -> L,R
LS,RS -> HRTF
Decode
L,C,R,LFE -> L,R
LS,RS -> HRTF
Decode
L,C,R -> L,C,R
LS,RS -> S
LFE -> L,R

Decode
L,C,R -> L,R
LS,RS -> LS,RS
LFE -> L,R,LS,RS

Decode
L,C,R,LS,RS,LFE ->
L,C,R,LS,RS,LFE
TBD

Discrete 5.1
(L,C,R,LS,RS,LFE)

L,C,R,LFE -> L,R
LS,RS -> HRTF
L,C,R,LFE -> L,R
LS,RS -> HRTF
L,C,R -> L,C,R
LS,RS -> S
LFE -> L,R
L,C,R -> L,R
LS,RS -> LS,RS
LFE -> L,R,LS,RS
---------------
TBD
Quad
(L,R,LS,RS)
L,R -> L,R
LS,RS -> HRTF
L,R -> L,R
LS,RS -> HRTF
L,R -> L,R
LS,RS -> S
---------------
L,R,LS,RS -> L,R,LS,RS
Derive LFE
TBD
ProLogic Stereo Decode
L,C,R -> L,R
S -> HRTF
Decode
L,C,R -> L,R
S -> HRTF
Lt,Rt -> L,R Decode
L,C,R -> L,R
S -> LS,RS

Decode
L,C,R -> L,C,R
S -> LS,RS
Derive LFE

TBD
Stereo
---------------
--------------- L,R ->L,R L,R ->L,R L,R ->L,R
Derive LFE
TBD
Mono Panned:
         3D-object:
M -> L,R
2-ch Pan or HRTF
M -> L,R
2-ch Pan or HRTF
M -> L,R
4-ch Pan or HRTF
M -> L,R
4-ch Pan or HRTF
M -> L,R
5-ch Pan or HRTF
Derive LFE
TBD
Input
Output
Headphones
(L,R)

Stereo Speakers
(L,R)

Dolby ProLogic
(L,C,R,S)

*post-mix encode*

Quad
(L,R,LS,RS)

Discrete 5.1
(L,C,R,LS,RS,LFE)

Discrete N-Ch
(7.1, etc.)

 

section 6


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1. Introduction  2. Speaker Summary  3. Executive Summary  
4. 3D API Group  5. M1D2 Group  6. Making Sense of Multi-Format Audio  
7. Consumer Reports Group  8. Rogue Group Report  9. Schedule and Sponsors