Low or No Background Audio:
Understanding SC 1.4.7
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.
Intent of this Success Criterion
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]
Specific Benefits of Success Criterion 1.4.7:
People who are hard of hearing often have great difficulty separating speech from background sound.
Examples of Success Criterion 1.4.7
(none currently documented)
Related Resources
Resources are for information purposes only, no endorsement implied.
Techniques and Failures for Success Criterion 1.4.7 - Low or No Background Audio
Each numbered item in this section represents a technique or combination of techniques that the WCAG Working Group deems sufficient for meeting this Success Criterion. The techniques listed only satisfy the Success Criterion if all of the WCAG 2.0 conformance requirements have been met.
Sufficient Techniques
Additional Techniques (Advisory) for 1.4.7
Although not required for conformance, the following additional techniques should be considered in order to make content more accessible. Not all techniques can be used or would be effective in all situations.
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)
Common Failures for SC 1.4.7
The following are common mistakes that are considered failures of Success Criterion 1.4.7 by the WCAG Working Group.
(No failures currently documented)
Key Terms
- CAPTCHA
initialism for "Completely Automated Public Turing test to tell Computers and Humans Apart"
Note 1: CAPTCHA tests often involve asking the user to type in text that is displayed in an obscured image or audio file.
Note 2: A Turing test is any system of tests designed to differentiate a human from a computer. It is named after famed computer scientist Alan Turing. The term was coined by researchers at Carnegie Mellon University. [CAPTCHA]
- audio-only
a time-based presentation that contains only audio (no video and no interaction)
- prerecorded
information that is not live