Using Reaper Automixer for Livestreaming

(Or: my journey for recording talk shows with multiple speakers in the same room)

Recently I shot and edited a series of local talk shows in Cantonese. The shows were shot in a small gallery with less-than-ideal acoustic characters, and the (3–4) speakers were sitting quite close to each other. I had them all mic’ed up with wireless lav mics, recording to a Zoom L8. There were quite a bit of voice bleeding into the other mics when one of the speakers spoke. The resulting audio recordings (regardless using the Master output or individual tracks) were quite echo-y. Normally it would take a skillful audio engineer to manually mix the tracks, which is hard and tedious work. We couldn’t afford to have this work done.

Then I learned about automixer. I first heard about automixer from one of the videos of the magnificent Curtis Judd. In this video, he talked about the Sound Devices MixAssist plugin, and compared it with the automixer feature in the Zoom F6. How automixer works is quite ingenious. If the signal level of any one of the channels is higher than all the other channels, then it is safe to assume that this channel contains signal from someone who is actually talking rather than just ambient noise. The automixer measures the signal levels from a bunch of channels, and lowers the signal levels of all channels except the one with the highest signal level, thereby suppressing the ambient noise in the other channels, making the final recording far less echo-y.

The first four episodes of the talk show were shot in one afternoon, so it was already too late to make use of one of these magic recording devices. Non did I want to drop another USD700–1,000 on yet another recorder (hey I already had a Zoom H5, an H6 and an L8).

Upon a bit of further research, I discovered Leandro Facchinetti’s video on using Reaper (the DAW software) to do automixing. There are two videos and I suggest you watch both to get the full details, but follow the instructions of the second video (which was more “developed”) to install the script (automating the task) and plugins.

From the 2nd (or the 3rd?) episode onward, I used Leandro’s script on Reaper for audio post-production, and the result was very noticeable, and I was quite pleased.

And then I thought: could I use Reaper as a virtual mixer doing automixing for live events, and feed the output to OBS? I find audio track routing confusing (to be quite honest I am still not confident that I fully understand it), and it took me quite some time to figure out a demo, as described and explained below. Note that I have yet to put it into practice, so YMMV.

To be able to do this, we need the following pieces of equipment and software:-

1. A computer capable of running Reaper AND OBS simultaneously. I tested it on my 2020 ASUS G14, but don’t see any reason why it wouldn’t work on one of those new M1 Macs.
2. An audio interface. The demo was conducted with a Zoom Livetrak L8. I also tested Reaper automixer with a Zoom H6 with success. The key thing is to bring the audio signals from a number of microphones into your computer. You would also need the appropriate audio interface software driver (most likely an ASIO driver) installed and working.
3. Reaper, with the leafac_Automixer plugin, Leandro’s automixer script and the ReaStream VST plugin installed. Reaper also needs to be using the appropriate ASIO driver and sees the various audio channels.
4. OBS. We would need a way to send the Reaper output to OBS. This is achieved by the ReaStream VST plugin running on Reaper (which sends the signal out via the network interface) and on OBS (which receives the signal). Try search for “Reaper OBS” on Youtube.

Once you have the automixer in Reaper working, add the ReaStream VST plugin to the automixer track. An oddity is that the automixer stops working when I tried to arm the automixer track for recording. This means Reaper could record the two microphone tracks, but not the automixer track (it could be render in post-production, but not while going live). Oh well. Note that you only send 2 Audio channels (the automixer channels), and not any of the other audio channels out.

For OBS to receive the audio signal sent out by Reaper, you need to add an “Audio Input Capture” and not “Audio Output Capture” (odd, I know). I used the excellent and very useful VB-Audio Virtual Cable (software virtual audio device for easy audio routing on Windows), then add the ReaStream VST filter.

Viola! And now it should work. Hope this helps.