Audio description is delivered as a second audio stream to your television or set-top box, and can be either 'receiver mixed' or 'broadcast mixed'.
With receiver-mixed audio description, the normal audio stream for the program is broadcast, while the second audio stream consists of the audio description narration only, along with signals that lower the sound level on the primary audio stream so that the descriptions can be heard.
With broadcast-mixed audio description, the second audio stream contains both the original soundtrack and the descriptions mixed into it.
Receiver-mixed audio description is often considered preferable for viewers because it allows them to control the volume of the audio description, and it can be fed to headphones so the viewer can hear it while others in the room hear only the original soundtrack.
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