Working with split stereo audio in REAPER

If you do a lot of collaboration with users of other DAWs, or a lot of mixing for other people, you’ll run into split stereo files pretty often. This article shows two ways to combine 2 mono files on separate tracks into a stereo file on one track. Both methods use basic REAPER functions so you do not need to use a separate program or create custom actions.

What is split stereo?

A split stereo file is a non-interleaved simultaneous recording that has the left and right channels in separate files. You can easily spot this in the filenames with “.L.wav” or “.R.wav” at the end.

Left and right shown in filenames

There’s nothing wrong with files like this, sometimes you prefer to have the Left and Right files combined on one track.

True stereo or duplicate mono?

Before you do anything, check that the two files are indeed a stereo pair. Click the mono button on the master, then invert the polarity of one of the split stereo files. If the sound completely disappears, you know the audio is the exact same on both files. It’s very common that the same exact signal is on both files, you can just delete one of the files in that case.

Perform a null test to check for stereo content

Workflow 1 – Folders

The most straightforward option is to pan the two tracks opposite, group the items and then turn an empty track above them into a folder.

Left and right combined with a folder track.

The benefit of this method is you can still apply processing to the left and right channels separately. The downside is that now instead of 2 tracks there are 3, which is 2 more than we wanted.

At this point you could then RT-Click on the folder track, go down to the Render/Freeze option and select “Render Tracks To Stereo Stem Tracks (and mute originals)”.

render the folder to stereo stem

Which now creates another track but with a stereo audio file on it. You can delete the previous 3 tracks.

Workflow 2 – Free Item Positioning

This method puts the two items on one track in lanes and both will play simultaneously.

Make a new track and drag the Left channel file onto it.
Enable “Free Item Positioning” for this track.
Shrink the height of the item a bit, then drag the Right channel file onto it.

Enable Free Item Positioning for the track

Then you just need to use the pan control in Item Properties (a double-click on the item should take you there).

Pan the media items hard left or right in the properties window.

That’s it. There are probably other ways but these are the two methods I use most often. Once you learn these methods you can accomplish the task in about 10 seconds.

EDIT 02.01.2013
I recently found a third option which works very well. If you have SWS Extensions installed you can use the “Implode items to takes and pan symmetrically” action.