Contrast




 * Accessed by: Analyze > Contrast...
 * [[Image:ContrastDialog.png|Image of the Contrast Analysis dialog]]

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, choose then:

Step One: Step Two: Result:
 * 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.
 * WCAG2 Help: Links to an external illustrated tutorial for using Contrast Analysis with the mouse.
 * Close: Closes the Contrast Analysis window, retaining foreground/background and result values for the duration of the Audacity session.

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