Re: [MMUSIC] Channel descriptions

Kevin Gross <kevin.gross@avanw.com> Fri, 20 July 2012 14:43 UTC

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Date: Fri, 20 Jul 2012 08:44:05 -0600
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From: Kevin Gross <kevin.gross@avanw.com>
To: Harald Alvestrand <harald@alvestrand.no>
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Cc: mmusic@ietf.org
Subject: Re: [MMUSIC] Channel descriptions
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I'm talking about a single audio signals. It a surround stream, a single
signal would be, for instance, the left front. Track is also a reasonable
description but people tend to associate that term with recording and
reproduction. The ability to label individual channels in surround formats
is important to distinguish the many formats and conventions in use. See
http://tech.ebu.ch/docs/r/r123.pdf.

In commercial applications, it is common, for efficiency, for multiple
loosely related channels to be carried in the same stream, e.g. different
background music source, paging signals for different zones. Active audio
crossover networks (http://en.wikipedia.org/wiki/Audio_crossover#Active) are
often used in large sound reinforcement systems and different frequency
components are carried to the speakers as separate channels in the same
stream.

In all cases it is important to correctly connect the channels to their
intended destinations. There are too many possibilities in most of these
use cases for the i= description to resolve the potential ambiguity.

Kevin Gross

On Fri, Jul 20, 2012 at 6:13 AM, Harald Alvestrand <harald@alvestrand.no>wrote:

>  Kevin,
>
> can you clarify what you mean by "channel" here?
>
> The term is used most often for components of a multisource audio signal,
> such as stereo, 5+1 or 22+2 - in most cases, those will be carried in a
> single SSRC, using an encoding that implicitly defines which channels go
> where.
>
> In WebRTC, we've converged on the word "track" for a single media flow
> such as one audio signal (mostly) carried in a single SSRC, and the word
> "stream" for multiple media flows (such as audio and video) that are
> related to each other in some fashion.
>
> If you have a definition you would like to use, please point to it - the
> discussion can get to be almighty confusing if we're not talking about the
> same thing!
>
>
> On 07/18/2012 01:57 AM, Kevin Gross wrote:
>
> The i= attribute provides a means to describe a session. Sessions often
> have multiple media streams or channels. Although RFC 3551 (page 8)
> suggests a convention for ordering of channels for surround sound
> applications, other applications use multiple channels in different ways.
> It would be useful if there were a mechanism analogous to i= for describing
> individual channels in a session. Does such a thing exist anywhere? I've
> searched the archives here and didn't find anything.
>
> Kevin Gross
> +1-303-447-0517
> Media Network Consultant
> AVA Networks - www.AVAnw.com <http://www.avanw.com/>, www.X192.org
>
>
>
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