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You may sometimes find it useful to use a mono audio clip as a stereo clip. The Treat as Stereo command applies a mono clip to a pair of left and right stereo channels.

You must use the Treat to Stereo command on a mono clip in the Project window before adding it to a stereo track in the Timeline window. A clip instance can't be converted to stereo when it's used in a mono audio track. Use the Treat as Stereo command on an instance of the clip in the Project window, and then drag it to a stereo track.

To use a mono clip as stereo:

In the Project window, select a mono clip.
Choose Clip > Audio Options > Treat as Stereo.

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