Using ReaRoute
In this video, we look at how to use ReaRoute to record audio in Reaper coming from any ASIO-capable audio application e.g. Ableton Live.
Discuss this tutorial here.
timestamp 0:21  Audio applications are usually connected using ReWire but Ableton Live doesn't allow VST plugins to be used when it is running as a ReWire slave. To work around this, we can use Reaper's ReaRoute instead.
timestamp 0:38  If it isn't already, install ReaRoute by running the Reaper installer.
timestamp 1:00  Ableton must be configured to use the ReaRoute ASIO driver instead of your normal one, so that the audio will be sent to ReaRoute instead of your soundcard.
timestamp 1:30  Each track in Ableton that you want to record in Reaper must be configured to send its output to a ReaRoute channel (instead of the master channel).
timestamp 2:12  In Reaper, create as many tracks as you need to record and configure them to get their signal from ReaRoute. Tracks must also be configured to record their output, not their input.
timestamp 3:18  Start recording in Reaper, then start playback in Ableton. If you go back to Reaper, you should see the audio being received and recorded on each track.
Don't forget to reconfigure Ableton to use your usual ASIO driver when you're done!