[Freeswitch-dev] Stereo support?

Anthony Minessale anthony.minessale at gmail.com
Fri Dec 14 03:17:06 MSK 2012

If everyone develops an interest in it and we can finde some equipment that
actually will take advantage of it then I am all for it.  I've just been
waiting for that to happen.  It does seem like that's pretty soon.....

On Thu, Dec 13, 2012 at 5:07 PM, Rick van Rein <rick at openfortress.nl> wrote:

> Hello,
> > the difficult part is how to figure out if someone is looked at
> > someone?
> Assuming that they delivered stereo microphone sound, which is a stretch in
> today's setups (a chicken-egg problem) it would be trivial I think.  You
> would basically do a calculation like
>         tan (alpha) = (R - L) / 0.5 * (R + L)
> and find in alpha the angle right from straight-forward.  Of course it is
> useful to dampen movements with a low-pass filter on momentary
> calculations,
> and/or to make these calculations over periods rather than for each
> individual audio sample pair.
> If the switch is aware what person is put in what position it could figure
> out which other is addressed.  That might call for a switch that does this
> work separately for each participant.
> I suppose it would be practical to imagine conference partners sitting in a
> circle.  N persons would be spread with 360 degrees / N apart.  If they
> spoke out under an angle alpha, than their i'th neighbour would hear the
> sound at an angle (alpha + i*360/N degrees).  And that angle would be used
> in the opposite way as the tangent-formula above.
> Sorry about the maths... I think it helps to clarify the approach though.
> If you'd like me to, I could try to find an elegant and *practical* way of
> modelling this with a simple matrix operation.  Let me know if you'd like
> me to contribute that.  It'd mean that mixing inputs and forming outputs
> from them is a nice operation with 2N inputs and 2N outputs with all the
> above isolated into a series of multiplications and additions.  Of the sort
> that would easily be met in hardware optimisations, if present.
> I'm sure that hardware vendors won't mind adding a layer of luxoury models
> for telephony... certainly not for business applications where they money
> is available... but AFAIK there are no stereo switches yet.  Imagine a
> good-quality codec (screwing ISDN, embracing OPUS) and the advantages of
> stereo communication, we could have a good laugh at all those people who
> still think 3000 Hz, audio-only and IPv4 define the VoIP arena.
> Cheers,
>  -Rick
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Anthony Minessale II

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