Re: Speaker Channel Layouts

Hello Olivier,

Wednesday, November 27, 2013, 10:43:39 AM, you wrote:

> A while ago we had a discussion on whether/how we should deal with
> “named” speaker layout, especially wrt channel ordering and up/down
> mixing. As a result, our spec currently only supports channel
> layouts up to 5.1, and we have some normative text in 

> I was recently made aware of work at the ITU which may be very interesting:

> The spec (about to be updated and which I gather should have a
> stable, ITU rec status in a matter of months) includes a “List of
> possible speaker positions for advanced sound systems” up to 22.2.

I wonder though how many of those are actually in use, and also
whether they provide any audible benefit.

> It also defines a naming scheme for any speaker positioning at key elevations.

> Unlike our current spec, the ITU work in progress does not,
> however, include mono (assumed to be trivial) or quad.

Quadrophonic was a extension of stereo to four channels, mainly to
sell extra equipment to enthusiasts. It died off for two reasons, one
being the lack of program material and the other being the lack of any
real audible benefit, even if you were rigidly seated in the sweet

> That said, it seems to me that this table would make it possible to
> support any speaker layout (assuming that the API can access the
> layout as a list of speakers using the standard scheme) and an
> up/down mixing algorithm based on positioning and adaptable to any setup.

Four channel ambisonic does actually provide an audible
benefit with four speakers. But rather than four independent
pan-potted channels, it is driven by the same four-channel WXYZ format
that 8 channel, or 8.2, or any other number of channels, is driven
from. W is the overall soundfield and X, Y , Z are the difference
channels in three dimensions. If you ignore height (Z) and front-back
(Y) then W,X is the same as mid-side stereo recording.

So adding a large number of independent channels looks like a
slippery slope and possible wasted effort, but adding support for
Ambisonic WXYZ allows that signal to be decoded down to 2, 2.1, 4.1,
5.1, 7.1 and so on all from the same signal.

  There are a number of disadvantages to this way of recording
  surround sound. One of the major issues is compatibility with
  formats with a different number of channels. The sound engineer has
  check compatibility with mono, stereo and 5.1. In the future the
  engineer may have to also check with 7.1, 22.2 and whatever other
  discrete channel surround system that may come next. That would
  require a lot of time and a room with enough speakers to cover every
  possible set up.

Best regards,

Received on Wednesday, 27 November 2013 14:30:31 UTC