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Re: Measuring Decibel Separation

From: David Woolley <forums@david-woolley.me.uk>
Date: Tue, 18 Sep 2018 18:50:11 +0100
To: w3c-wai-ig@w3.org
Message-ID: <8ef2059c-d3f3-6c04-9dd6-42c1e3bc4e5d@david-woolley.me.uk>
On 18/09/18 18:23, Greg Gay wrote:
> How does one measure whether speech in multimedia is 20db louder than 
> background sound, from an auditing perspective.
> 
> During production its easy enough to control speech and background 
> levels, but what I'm looking for is a way to show clients post 
> production, that the speech volumn level in a video is less than 20db 
> greater than the volume of the background audio in that video. (re WCAG 
> 2.1 SC 1.4.7)

This really needs to be done white box to properly demonstrate 
compliance, but 20dB is 10 times more power, so, I'd suggest determining 
sections of the audio with no speech and measuring peak amplitude 
(probably fast A weighted**), then measuring the peak amplitude in a 
section with speech.  If the ratio is more than 11 times power (about 
20.8 dB, say 21 dB)you are getting close to complying, although one 
needs some safety margin to account for poor selection of the quiet and 
speech sections.

You'll need to exclude the periods with the allowable occasional sounds, 
first.

** The criteria should specify this, although they appear not to do so!
Received on Tuesday, 18 September 2018 17:51:13 UTC

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