Understanding WCAG 2.0

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Low or No Background Audio:
Understanding SC 1.4.7

1.4.7 Low or No Background Audio: For [begin add]prerecorded audio-only[end add][begin delete]audio[end delete] content that (1) contains [begin add]primarily [end add]speech in the foreground, (2) is not an audio CAPTCHA [begin add]or audio logo[end add][begin add], and (3) is not vocalization intended to be primarily musical expression such as singing or rapping[end add], 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 sound[begin add]s that last for only one or two seconds[end add][begin delete] effects[end delete].

    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

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.

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)

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


a time-based presentation that contains only audio (no video and no interaction)


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]


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