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New proposal for issue 287 (volume control)

From: Ian Jacobs <ij@w3.org>
Date: Mon, 03 Jul 2000 18:48:39 -0400
Message-ID: <39611847.E60D02FF@w3.org>
To: w3c-wai-ua@w3.org
Hello,

Today, Jon and I discussed issue 287 (about audio volume 
checkpoints) [1] (refer to resolution to keep one checkpoint
about global control and one about independent control of
audio sources [2]). Jon made the following comments:

1) Independent control of audio volume is more important
   for synchronized presentations than for non-synchronized
   content. When content is not intended to be synchronized,
   users don't need to worry about competing volumes as long
   as they can play the sources independently. Global volume
   control suffices when you can play different audio sources
   independently. This is covered by the checkpoint to
   start, pause, resume, etc. audio.

2) Speech synthesizer volume is generally handled globally
   for applications, not on an application-by-application
   basis.

3) "Too much control" (namely, the ability to change the 
   volume of independent audio sources played simultaneously)
  
   may require such complex interaction as not to promote
   accessibility in practice. Are we requiring midi user agents
   to provide an interface to control the volume of each track?
   An equalizer tool (fairly comment to control relative volumes)
   does not typically work on individual components but on
   frequencies. Would that meet the requirements of this checkpoint
   nonetheless?

4) This is a fairly serious change of scope from the
   previous checkpoints about volume.

5) This discussion suggests a content issue: should the WCAG
   be recommending that authors provide content in recognizable
   tracks (e.g., a SMIL presentation) as opposed to formats
   without tracks (e.g., a WAV file)?

Based on these comments, I'd like to propose that we reconsider
the resolution. I have the following wording for the proposed
checkpoint (proposed, but in no document yet):
   
   "Allow the user to control independently the volumes of
    audio sources recognized as distinct."

I propose we create two checkpoints instead to emphasize
the critical cases and to reduce the scope of the
change:

<NEW 1>
   "Allow the user to control independently the volumes
    of audio sources synchronized to play simultaneously.
</NEW 1>

<NEW 2>
   "Allow the user to control the synthesized speech volume
    independently of other sources of audio."
       Note: It is expected that speech synthesizer volume will
             be set at the system level.
</NEW 2>

Notes:

 - The second checkpoint is much closer in scope to the
   previous version of the speech volume checkpoint. For
   example, from the Candidate Recommendation:

     "Allow the user to configure synthesized speech volume."

   However, the new version talks about control and not
   just configuration. 

 - As usual, if the UA cannot determine that two sources of
   audio should be played simultaneously, the first 
   checkpoint does not apply.

Comments welcome,

 - Ian
     
[1] http://cmos-eng.rehab.uiuc.edu/ua-issues/issues-linear.html#287
[2] http://lists.w3.org/Archives/Public/w3c-wai-ua/2000AprJun/0506.html

-- 
Ian Jacobs (jacobs@w3.org)   http://www.w3.org/People/Jacobs
Tel:                         +1 831 457-2842
Cell:                        +1 917 450-8783
Received on Monday, 3 July 2000 18:48:43 GMT

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