From Audacity Manual
- Accessed by:
To use Contrast Analysis, select in either a single mono speech track, or in the left or right channel only of a stereo speech track.
If you have an unsplit stereo track (meaning that it states "Stereo" to left of the waveform), use the , choose , then select in either the resulting left or right channel.
With the single track selected, choosethen:
- Select a region containing the speech (this is the "foreground" selection)
- Click the button in the "Parameters" box in the "Foreground:" row; the start and end times of the selection will be displayed
- The average RMS of the selected foreground audio will be displayed in the "Volume" box at the end of the row.
- Select a region containing only the background sound (this is the "background" selection)
- Click on the button in the "Parameters" box in the "Background:" row ; the start and end times of the selection will be displayed
- The average RMS of the selected background audio will be displayed in the "Volume" box at the end of the row.
- Contrast Result: Shows if the difference between foreground and background gives a pass or fail against the "WCAG 2.0, Success Criteria 1.4.7" guideline for accessible audio. A pass is given if the difference is 20 dB or more.
- Difference: The actual average RMS difference value found.
- Reset: Clears all the parameters and result values.
- Export: Saves the foreground/background values and the result to a text file for proof that you checked your audio file. If you export again to the same file, the new result will be appended underneath the previous one.
- Help: Links to this "Contrast" page.
- Close: Closes the Contrast Analysis window, retaining foreground/background and result values for the duration of the Audacity session.
|To ensure the track is fully compliant with WCAG2, you should check the contrast between foreground and background in several places.|