Understanding SC 1.4.7:Low or No Background Audio (Level AAA)

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.

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.

About Decibels

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. However, it is not necessary to use these particular techniques. For information on using other techniques, see Understanding Techniques for WCAG Success Criteria, particularly the "Other Techniques" section.

Sufficient Techniques

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

Key Terms

audio

the technology of sound reproduction

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"

CAPTCHA tests often involve asking the user to type in text that is displayed in an obscured image or audio file.

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

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.

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

Video can be made up of animated or photographic images, or both.