Understanding Success Criterion 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:

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.

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

Intent of Success Criterion 1.4.7: Low or No Background Audio

The intent of this Success Criterion is to ensure that any non-speech sounds are low enough that a user who is hard of hearing can separate the speech from background sounds or other noise foreground speech content.

The value of 20 dB was chosen based on Large area assistive listening systems (ALS): Review and recommendations [[LAALS]] and In-the-ear measurements of interference in hearing aids from digital wireless telephones [[HEARING-AID-INT]]

Benefits of Success Criterion 1.4.7: Low or No Background Audio

Examples of Success Criterion 1.4.7: Low or No Background Audio

Resources Success Criterion 1.4.7: Low or No Background Audio

Techniques for Success Criterion 1.4.7: Low or No Background Audio

Sufficient Techniques

  1. Mixing audio files so that non-speech sounds are at least 20 decibels lower than the speech audio content

Advisory Techniques

  • Providing a way for users to adjust auditory levels of foreground and background sound independently (future link)
  • Providing an audio track for synchronized media that includes background sounds that are at least 20 decibels lower than speech (future link)

Failures