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Re: Action item. definition and use of Clean audio in European television

From: Janina Sajka <janina@rednote.net>
Date: Sat, 14 May 2011 21:25:20 -0400
To: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Cc: Sean Hayes <Sean.Hayes@microsoft.com>, "HTML Accessibility Task Force (public-html-a11y@w3.org)" <public-html-a11y@w3.org>
Message-ID: <20110515012520.GA9893@sonata.rednote.net>
Amazing how much easier it is to find information when you can search on
the name everyone else has been using! Thanks, Sean, for ferreting out
this critical datum.

Yes, I believe we should adjust our docs and requests. No reason to go
against the flow.

With respect to independently adjusting volume of channels (or their pan
positions, etc), may I suggest we've asked for that in our User
Requirements?

     * (DV-5) Allow the author to independently adjust the volumes of
     * the audio description and original soundtracks.
          * (DV-6) Allow the user to independently adjust the volumes of
	  * the audio description and original soundtracks, with
	         the user's settings overriding the author's.
			          * (DV-8) Allow the author to provide * fade and pan controls to be
				  * accurately synchronised with the * original soundtrack.
     * (DV-11) Support the simultaneous playback of both the described * and non-described audio tracks so that one may be
            directed at separate outputs (e.g., a speaker and headphones).

Janina

Silvia Pfeiffer writes:
> On Sat, May 14, 2011 at 1:33 PM, Silvia Pfeiffer
> <silviapfeiffer1@gmail.com> wrote:
> > Ha, that's funny: have we been using the wrong term all the time?
> >
> > In out requirements it's called "clear audio" (and that's also what we
> > have requested in the bug, see
> > http://www.w3.org/Bugs/Public/show_bug.cgi?id=12544 ). In these
> > documents it's called "clean audio".
> >
> > I think we will need to change our documents/request for @kind label...
> >
> > I've now (using the proper name) also found this document:
> > http://www.etsi.org/deliver/etsi_ts/101100_101199/101154/01.09.01_60/ts_101154v010901p.pdf
> > which is "Digital Video Broadcasting (DVB); Specification for the use
> > of Video and Audio Coding in Broadcasting Applications based on the
> > MPEG-2 Transport Stream" . Annex E talks about Clean Audio as a
> > supplementary audio service in the form of receiver-mixed data. This
> > is in contrast to broadcast-mixed delivery, which would be as a
> > separate alternative audio stream, which DVB does not support.
> >
> > So, it seems that while we are asking for a @kind="clean audio" label
> > on audio tracks that are delivered separately to the main audio track
> > and provide a better understandable audio mix, this isn't actually
> > what DVB supports (and I assume DVB is the only way in which clean
> > audio is currently realized?).
> >
> > So, the question is: what do we do in HTML5 to support the kind of
> > clean audio tracks that DVB expects.
> >
> > IIUC, the receiver-mixed means of delivery of clean audio (and audio
> > description for that matter) delivers it through multi-channel audio
> > but within the main audio track. This means, on a 3, 5.1 or more audio
> > channel file, some of these channels are reserved for non-main audio.
> 
> Actually, that's incorrect for audio description. A "supplementary
> audio" channel is an additional audio channel, so it would take up the
> number of audio file with stereo, they would deliver 3 channels, for
> one with 5.1 it would have 7 channels etc. I think though for clean
> audio it is still true that they use center channel for speech only in
> a 5.1 file.
> 
> Now the big question is: how common is all this. And would we
> encourage people to rather provide multitrack than multichannel for
> accessibility needs?
> 
> Cheers,
> Silvia.
> 
> 
> > There is a marker of "visual impaired commentary" for AD and "hearing
> > impaired" for clean audio used on the individual channels that have a
> > separate use.
> >
> > The images shown in the spec show the use of clean audio only in the
> > case of 5.1 channels with the center channel used for clean audio,
> > while when using audio description it shows the use of 3 channels:
> > left, right, and a mono audio description.The user has the possibility
> > to separately increase the volume of the audio description and of the
> > clean audio.
> >
> > If such a file with multiple audio channels was to be used in a HTML5
> > page, we wouldn't get the same level of control that DVB has defined,
> > because there is no control that allows to change the volume mix of
> > multi-channel audio. It is important to understand that there is a
> > difference between multi-channel audio and multi-track audio:
> > multi-channel audio is encoded within one audio track just by
> > interleaving the channels within that track. In HTML5 we don't have a
> > means to change the volume of the individual channels, but only to
> > change the volume of a track.
> >
> > Cheers,
> > Silvia.
> >
> >
> > On Fri, May 13, 2011 at 7:59 PM, Sean Hayes <Sean.Hayes@microsoft.com> wrote:
> >> Here is a summary of the European digital television definition for clean
> >> audio [adapted from a forthcoming edition of TS 101 154 from the DVB]. The
> >> system relies on client side mixing, under control of the programme-maker.
> >>
> >>
> >>
> >> Clean Audio refers to audio providing improved intelligibility. It is
> >> targeted for viewers with hearing impairments, but can as well serve as
> >> improvement for listening in noisy environments.… an important requirement
> >> is to adjust, on a passage by passage basis, the relative level of programme
> >> sound in the mix which the secondary audio user hears. The programme maker
> >> is best able to determine the level under controlled conditions when
> >> authoring the secondary audio information to modulate the level of programme
> >> sound in the secondary audio capable receiver so suitable secondary audio
> >> information is thus transmitted within the secondary audio stream.
> >>
> >>
> >>
> >> Individual secondary audio users will have different aural acuity, and there
> >> are, in practice, differences in audio signal level for different home
> >> receivers. An essential requirement is for the user to be able to adjust the
> >> volume to suit his/her condition.
> >>
> >>
> >>
> >> A descriptor is sent in a service to indicate a clean audio service. The
> >> level by which the main audio service should be attenuated is sent in the
> >> metadata (on a per channel basis). The client should accentuate the levels
> >> of the channel containing the dialogue and attenuate the other channels,
> >> accordingly. The level of the centre channel added should additionally be
> >> under user control to allow individual tailoring of the sound for
> >> audibility.
> >>
> >>
> >>
> >> Background:
> >>  http://www.rnid.org.uk/VirtualContent/84923/background_noise_PDF.pdf
> >>
> >> European HD TV requirements: http://tech.ebu.ch/docs/tech/tech3333.pdf [p15]
> >

-- 

Janina Sajka,	Phone:	+1.443.300.2200
		sip:janina@asterisk.rednote.net

Chair, Open Accessibility	janina@a11y.org	
Linux Foundation		http://a11y.org

Chair, Protocols & Formats
Web Accessibility Initiative	http://www.w3.org/wai/pf
World Wide Web Consortium (W3C)
Received on Sunday, 15 May 2011 01:25:55 GMT

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