35. Audio Clarity & Contrast

When you have the opportunity to set the volume of speech relative to volume of background sound:

• Allow the user to access the foreground speech without the background sound (e.g. control to turn off background sound, separate volume controls)
  OR
• Set the background sound to be 20 decibels lower than the foreground speech

Rationale

This guideline is based on a WCAG 2.0 Level AAA guideline. Level AAA guidelines are advanced guidelines that aren’t always possible or required. In general, the PGs do not cover Level AAA guidelines.

This guideline, however, offers valuable information on how to allow people with hearing impairment to distinguish foreground speech from background sounds.

As such, this PG is included to provide guidance for cases where we do have the opportunity to set the difference between foreground and background volume.

When we do not have this opportunity, captions - see Pearson Guideline 37 will ensure that the information provided by the audio is available to these users. However, for those with minor hearing impairments, the user experience will be better when this PG is followed.

General Techniques

This is not required when:

• Foreground and background sound are recorded together
• You are reusing audio files that have already been finalized

Testing

Testing technique	Description
Review	While you are testing for either Pearson Guideline 36 or Pearson Guideline 37, notice whether it is difficult to pay attention to the main audio content due to loud background noise or music. If so, look to see whether there are user options that would improve this, like the ability to adjust foreground/background volume separately.
Analysis	If you find there’s no way to achieve a comfortable listening experience, report this as an error.

Related Guidelines

WCAG 2.0 Level AAA 1.4.7 Low or No Background Audio

For prerecorded audio-only content that (1) contains primarily speech in the foreground, (2) is not an audio CAPTCHA or audio logo, and (3) is not vocalization intended to be primarily musical expression such as singing or rapping, at least one of the following is true: (Level AAA)

• No Background: The audio does not contain background sounds.
• Turn Off: The background sounds can be turned off.
• 20 dB: The background sounds are at least 20 decibels lower than the foreground speech content, with the exception of occasional sounds that last for only one or two seconds.

Note: Per the definition of “decibel,” background sound that meets this requirement will be approximately four times quieter than the foreground speech content.