Anyone who mixes for hire knows the scenario: A client sends a song to be mixed without individual drum tracks (snare, kick, etc.) that are instead embedded in a single track. I'll send an email, "Hey, can I get the actual tracks for the drums so I can really mix your song?" They then email back an excuse as to why this is the only version of the drums they have. WaveMachine Labs, known for the venerable drum replacement app Drumagog [Tape Op #84], have created ReStem, a standalone app and plug-in (both non-real time) that will de-mix a stereo or mono drum submix into seven parts: Kick, Snare, Hi-Hat, Toms, Ride, Crash, and Other. The app looks like a simple stereo mixer, with the seven sources each having level knobs, mute and solo buttons, Gate and Shaper controls, plus the Kick and Snare channels even have Drumagog installed if there's a need to replace or blend in a new sound. But does this AI-trained software work? Yup!
I took a stereo drum submix stem from a session I mixed on my console last year. The drummer's parts were not simple, with intricate but subtle hi-hats and intense tom patterns in some sections. It took about two minutes for the standalone app to process the track after I loaded it in. Note that this is all being done on your computer, and unlike some de-mixers it is not handled remotely – no need for an internet connection. I was amazed to hear the hi-hat extracted from the submix, and all the other sources as well. It was easy to increase/decrease the level of any track in the new mix via the app, which could be the lifesaver we sometimes need, like when clients ask me for revisions to an analog console mix.
As with any de-mixing program, playing the separated tracks together often sounds artifact-free, but when soloing an isolated source, I would sometimes hear unwanted residual pumping noise (especially on the Crash track) that can create a tremolo sound from the parallel compression and bleed in the original submix. It was funny to solo ReStem’s Other track, revealing scratch vocal and guitar bleed from the live backing track take! Mute that, and there’s no more weird stuff in the background. As I examined the separated tracks further, I was gradually more impressed by the processing quality, as there were only a few times that I heard much of anything that was not the intended sound. WaveMachine Labs trained AI to understand and discern between the actual components of a drum kit, and it seems to have worked. It can also separate drum machine stems, which I tried it out on a previously mixed project while wishing for a time machine. Next time, I'll be using ReStem. Though the GUI’s cleanly laid-out mixer interface is convenient and versatile, it can also de-mix and export the seven new files. Handy – especially if there's a need to edit, cut parts out, or apply new processing – compression, EQ, reverb, and such. If sampled drums were added or transients and Gates applied, it can export either the processed or raw stems, plus it can include the full new audio submix from the app. There’s also a ReStem Core version for only $99 that is basically just the standalone app with no plug-ins, Drumagog, Gate, or Shape features.