How do I convert a mono clip (already on the timeline) to a stereo clip?

Create a New Project-Create New Sequence-Right CLick on the Sequence in your Project window-Go to modify-Audio Channels-make sure it is set to Stereo. Open MONO project-Copy Your Video and audio clips from your edited timeline- Paste them into the new Projects sequence. Unfortunately, if you have multiple sequences, you must do this for each. 

Had this issue and nothing was working. Didn't make sense to me because it was a stereo clip, but later when it was already edited in the timeline it went to mono. Tried the options in this forum, tried exporting as a Stereo WAV file to reimport, etc. Nothing worked.

Messed around and found a solution on my end:

Right click the audio track on the timeline > Track Output Channel Assignments > Check off Channel 1 and 2 under the same channel (or depending on how the audio was recorded it may be a different variation) and then it reverted back to a stereo clip for me instead of mono.

Not too sure how it went to mono, and not sure why the other options didn't work for me. Just wanted to add my solution to the mix incase down the line someone else needed more trouble shooting options! 

Right click the audio file in your project panel.

Modify > Audio Channels

Change from stereo to mono.

Add the clip to your timeline and it will play across both channels.

I have CS4 and none of the fixes worked for me, but I found that if you exported just the audio as a MP3 file and then imported it the sound the result will be Stereo. you may have to adjust the length of the audio.

Figured out the solution. Just right click your sequenc and go to Sequence settings. Under Audio change the number of channels from 1 to 2. That will do the trick.

Here is our Solution in Tips 2 Fix 

https://youtu.be/0F-B61MoqNE

I did find the stereo expander plugin and turned the feild all the way to narrow and that got the desired result for me.

I fixed it by making the track balance central, so it is possible, and easy!

Though it was a bit temperamental. Seems ok at the moment though.

Danny,

I always thought of mono as "the same in both channels." Are you referring to a clip that is mono but not being heard equally in L and R? I just want to make sure I understand. I've had to do a lot of work lately with 2-channel stereo audio (where two interview subjects each have their own mic, and I have to do the "fill left" or "fill right" mentioned above)...but I wasn't sure if this is what you meant.

You mentioned working with the file in Audition - could you replace the existing file in Premiere with the reworked version?

Right click the clip in the timeline. Hit Show in Project. Right click the audio and click Modify / Audio Channels. Change Preset and/or Clip Channel Format to Stereo. Double click to verify in Source window the clip is playing in stereo. Go back to clip in timeline. Match frame and replace.

-- Tom