Monday 16 March 2015

Converting from mono/stereo to multi-channel wav files (Reaper guide)

Sometimes you need to take several mono or stereo wav files and collate them together into a single multi-channel file. This is particularly pertinent for ambisonics and for B-format audio in general. I'm writing this because I couldn't find a decent set of instructions online and I had to figure it out myself.

Yesterday I had four mono files that I had captured with an ambisonic mic and a field recorder. The field recorder spits out a mono wav file for each of its inputs. I wanted a single, four-channel file that I could process and spatialise in Reaper using ambisonic decoding plugins.

I took the four files and dragged them into Reaper on separate tracks. When you drag in a bunch of files it asks whether you want them on separate tracks or the same one. Hit the separate tracks button.
Then I clicked on the I/O button on the master bus and set it to have 4 track channels instead of two.

After that I made a new track and did the same thing; setting it to four channels in the I/O menu. Then I made a send from each of the four mono channels (the ones with my audio in them) to the new 4-channel track. In the I/O window of each of the audio tracks, turn off the master/parent send so the audio doesn't mix together in the master bus. At the bottom of the send box in the I/O window, you can set how many and which channels (from the track you're sending from) go to which channels in the recieving track.

I set my first audio channel to have 1 mono send, sent to channel 1 on the recieving track. My second track I set to have 1 mono send, sent to channel 2 on the receiving track; and so on. When I finished all of that I went to File > Render and rendered out my 4-channel wav file. You have to specify 4 channels in the Render window too.

I hope this quick guide was useful and that it saves someone much time and brain-hurt. Also: Future Morgan, if you forget how to do this, you're welcome.



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  2. is there any tool for conversing Stereo Audio to 4-Channel Audio?
    i want to make a Spatial Audio for My 360 VR Video... so what would be the Process of The..

  3. Is that for a 3D video on YouTube? YouTube has specific guidelines here:
    It looks like it just needs to be in ambisonic format, which is a simple job of importing the audio into a DAW like Reaper, using a stereo => ambisonic encoding plugin (like the stereo planewave encoder in Trond Lossius' ATK) and then rendering it out as a 4 channel wav file, which you then encode with your video before uploading to YouTube.
    Hope it goes well!

  4. So helpful, thanks a million. Once the track is multichannel, does that mean it is A-Format and you must use an AtoB encoder to create a B-format track? If so, would you put that encoder on the Master bus? Thanks again.

    1. Yup, you've got it. You could put that encoder anywhere (check out trond lossius' Ambisonic Tool Kit if you need one) but you'll need to put it before any other ambisonic processing you're going to do.
      So if you put it on the master bus, all your processing will need to go after it.
      The most important thing to remember is to change the number of channels on your tracks from 2 to 4, so that the ambisonic stuff can work properly.

  5. Morgan, how would I take two stereo files, make them into a 4 channel wav file, but instead of the (R) stereo out, coming from the first stereo channel to land in the second lane of a 4 channel wav file, have it land in the third lane? I'm actually wanting to move 3 of the four lanes of the 4 channel audio. If I initially record Left in and record stereo out and then record right input with stereo out I essentially get LL LR RL and RR. I need LL, RR, LR and RL. Hope I'm not complicating things, but do you understand where I am going and how would I do this?