Understanding SC 1.4.7: Low or No Background Audio (Level AAA)
In Brief
- Goal
- Prerecorded speech is not disrupted by background sound.
- What to do
- Avoid or lessen background sound, or let users turn it off.
- Why it's important
- People who are hard of hearing may have difficulty distinguishing speech from music and other sounds.
Success Criterion (SC)
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.
Note
Per the definition of "decibel," background sound that meets this requirement will be approximately four times quieter than the foreground speech content.
Intent
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
- People who are hard of hearing often have great difficulty separating speech from background sound.
Related Resources
Resources are for information purposes only, no endorsement implied.
Techniques
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. A technique may go beyond the minimum requirement of the criterion. There may be other ways of meeting the criterion not covered by these techniques. For information on using other techniques, see Understanding Techniques for WCAG Success Criteria, particularly the "Other Techniques" section.
Sufficient Techniques
Key Terms
- audio
the technology of sound reproduction
Note
Audio can be created synthetically (including speech synthesis), recorded from real world sounds, or both.
- audio-only
a time-based presentation that contains only audio (no video and no interaction)
- CAPTCHA
initialism for "Completely Automated Public Turing test to tell Computers and Humans Apart"
Note
CAPTCHA tests often involve asking the user to type in text that is displayed in an obscured image or audio file.
Note
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.
- live
information captured from a real-world event and transmitted to the receiver with no more than a broadcast delay
Note
A broadcast delay is a short (usually automated) delay, for example used in order to give the broadcaster time to cue or censor the audio (or video) feed, but not sufficient to allow significant editing.
Note
If information is completely computer generated, it is not live.
- prerecorded
information that is not live
- video
the technology of moving or sequenced pictures or images
Note
Video can be made up of animated or photographic images, or both.