Friday, August 22, 2008

Diamondware spatial conferencing

Just read this on Alec Saunders fantastic blog

Interesting concept, makes me wonder if it is possible in Asterisk to ‘adjust’ the left/right mix for audio conference participants?
(Yeh I know there is only one channel in a telephone call but you get what I mean).

It’s probably covered under patents etc but has anyone tried to ‘spatially separate’ audio mixes for each participant in an Asterisk conference call?

This is a poor example but basically as you dont have 'stereo' in a phone call but I was thinking an equation something like this.

Number of speakers in a conference room = 'N' deviations

Range = 80% (obviously you couldn't do 100% otherwise would be silent in outer channels once you get over 10 participants.

(50/50 + / - the deviation N / range)

So in the example of a conference room with 3 participants deviation 26%

Caller 1 = 76% L + 24% R (-1 deviation of 26%)
Caller 2 = 50% L + 50% R (norm default 50/50)
Caller 3 = 24% L + 76% R (+1 deviation of 26%)

Example of a conference room with 7 participants deviation of 11%

Caller 1 = 83% L + 17% R (-3 deviations of 33%)
Caller 2 = 72% L + 28% R (-2 deviations of 22%)
Caller 3 = 61% L + 39% R (-1 deviations of 11%)
Caller 4 = 50% L + 50% R (norm default 50/50)
Caller 5 = 39% L + 61% R (+1 deviations of 11%)
Caller 6 = 28% L + 72% R (+2 deviations of 22%)
Caller 7 = 17% L + 83% R (+3 deviations of 33%)

BTW in case you ae wondering where you have heard the name Diamondware before - they were the guys that provided 3D audio for Second Life that was virtual distance related eg. sounded louder if your avatars were close together or quieter if they were further apart.

The company I was working for Mexuar was the first company to get voice into Second Life but ours was just you could either hear or not hear the audio based on your location so although we beat them to market by a few months theirs was the better solution (although way more expensive - using open source products like Asterisk enabled us to do a very very cost effective voice audio solution for virtual worlds that was highly scalable)


  1. Dean,

    The trouble is there's more to it than just the relative level of the left vs right channels. Spatialization involves slightly more complex issues of timing & phase that relate to the shape of the human head & pinnae. These are often referred to as "HRTF" for Head related transfer functions.

    However, recent advances in DSP technology mean that digital audio processors that used to cost $$$ can now be had ridiculously cheap. Behringer makes a phantom power capable, A/D convertor with compression, limiting & stereo effects....all for $79 retail.

    Spatial effects could happen in telephony, if someone wants it bad enough. It would certainly makes sense in telepresence.

    But simply using two channel stereo would be a fruitless cop-out.

  2. Sure Michael....but until you get a carrier to implement a telephone thats capable of doing 3 axis audio - then left and right conferencing through current headphones/microphones is the perfect solution for the technology we have available today....rather than wishing for something that may never come.

    Someone in the asterisk community could code this up in a weekend - what you are proposing is similar to the 5.1/6.1/7.1 speker arrangement that the home theatre vendors have been arguing over for years.