I can’t imagine that this will be a lot of use to many people but when I needed to do split a stereo track into two mono tracks I couldn’t find any help. After a fair bit of experimentation I finally figured out how to do it and thought it would be worthwhile documenting the method I used.
The background was that I had a recorded Skype telephone call which I needed to edit down. The call recording software I use allows you to pan each side of the call on the recorded mp3. I wanted to be able to work on each end of the call independently, mainly to set the levels, so that they were about the same.
First step is to add a new track and import the mp3 file onto that track.
I then duplicate that track, so that I have two versions of the same thing (right click on the track and choose “Duplicate”). I name the tracks “Original Call” and “Duplicate”
Next I set up two new empty tracks called “Left” and “Right”.
Now comes the interesting bit. We’re going to use Reaper’s excellent patching and routing capabilities. I’m going to route the left side of “Original Call” to the track called “Left”, and the right side of “Duplicate” to the track called “Right”.
On the “Original Call” track, click the small “io” button just above the pan slider. Set up a new send, routing the signal to the track called “Left”. We only want the left channel so, from the drop down boxes, select Audio 1 => 1.
We do the same with the “Duplicate” track, sending it to the track called “Right” and selecting Audio 2 => 2.
Now select the tracks called “Left” and “Right” (click “Left” and then shift-click “Right”), then right click and choose “render to mono stem”. This creates your two separate mono tracks, called “Left – stem” and “Right – stem”.
If you wish you can delete “Original Call”, “Duplicate”, “Left” and “Right”, but I prefer just to mute them (as in the screenshot above), just in case I need to go back and redo any step.