A different stems model and much faster reloads for rekordbox's STEMS, on the Mac. Free and open source.
What it does · What you get · Install · FAQ · Troubleshooting · Get help
Stems are the parts of a track pulled apart: vocals, drums, bass and the rest of the music (rekordbox calls it Inst). With STEMS in rekordbox you can mute or solo each part live, for example drop the vocals for an instrumental or keep only the vocals for an acapella. rekordbox works the stems out on your Mac with a "model": a program trained to tell the parts apart.
RB Stems Plus is a small app with two features:
- Demucs v4: a different stems model. It swaps rekordbox's model for Meta's Demucs v4, the newer version of the open source separation model that rekordbox's own is based on. It doesn't change the rekordbox app.
- Stems Cache: much faster reloads. rekordbox separates a track again every time you load it. Stems Cache keeps the stems it already made, so the next time you load that track they come back in seconds, without separating the track again. It works with either model, rekordbox's own or Demucs v4, and it changes one file inside rekordbox (see Honest risks).
Install either one, or both.
rekordbox's own model is Demucs v3, retuned by Pioneer. Demucs v4 is Meta's newer version. They split some sounds differently, and which split is better depends on the music, and on the stem:
- Pop, rock and rap: on MUSDB18, a standard test of 50 songs with their real stems, Demucs v4 came closer to the real stems on every stem: bass on 45 of 50 songs, drums on 44, the rest of the music on 41, vocals on 36.
- Electronic tracks: on six electronic productions with their producers' stems, Demucs v4 was closer on drums and bass (about 2.5 dB at the median, roughly 40% less bleed), and rekordbox's model on vocals and the rest of the music. Not on every track: one went to rekordbox's model on bass too.
- Rumble techno: on Lunfardo by Ignez, rekordbox's model keeps a short low note before each
kick in the bass stem. Demucs v4 puts it in the drums until the track opens up, and to our
ears rekordbox's split was closer. We tried many other models on the same minute and got
different results from each:
- Meta's htdemucs (the same model, run outside rekordbox), htdemucs_ft and mdx_extra, and ZFTurbo's SCNet and BS-RoFormer did the same;
- Demucs v4's six-stem version and Meta's original Demucs v3 caught part of it;
- AudioShake and Ableton Live's stem separation each made yet another split.
- Synthetic techno loops with known stems: close. With a held sub bass Demucs v4 came closer on average. With short rolling bass notes both did much worse, and rekordbox's model was slightly closer on 5 of 8 loops.
So try both on your own tracks and keep the one you like. Uninstall Demucs v4 puts rekordbox's model back any time, and Install Demucs v4 brings it back. Stems Cache works with both and keeps the stems saved with each.
Demucs v4 does more work, so the first STEMS on a track takes longer. Stems Cache saves the stems once a track is separated, with either model, so every later load is much faster.
Timed in rekordbox on an Apple Silicon Mac, from loading a 6½-minute track to its stems being ready. Demucs v4 separates about 5 times faster than the music plays, rekordbox's own model about 15 times.
Memory: rekordbox's own model uses about 1.42 GB at its peak. The Demucs v4 model, run with rekordbox's usual settings, peaks at about 2.30 GB. With Stems Cache installed it runs with a leaner setting and peaks at about 1.52 GB, with the same speed and the same stems.
- A Mac. Tested on macOS 26 Tahoe on an Apple Silicon Mac.
- rekordbox 7 in
/Applications/rekordbox 7, with STEMS working, and turned on at least once so rekordbox has downloaded its STEMS Engine (the files STEMS needs). - An administrator account on the Mac (the one that can install apps), for Stems Cache.
- Disk space: about 1.5 GB for RB Stems Plus (the model, a spare copy, and the copies of rekordbox's files it keeps so it can put them back). The app checks first and says if it needs more. Then room for saved stems: at most 20 GB by default, which you can change.
Stems Cache stops saving new stems when your disk gets low: under 10% of the disk free, 50 GB at most (about 25 GB on a 256 GB Mac). Stems it already saved still load.
Where to find STEMS in rekordbox: Preferences › Extensions › STEMS, with Enable the STEMS Function on.
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Quit rekordbox.
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Open Terminal (press Cmd+Space, type Terminal, press Return), paste this line and press Return:
curl -fsSL https://github.com/Gabe-LS/rbstemsplus/releases/latest/download/bootstrap.sh | bashIt puts RB Stems Plus in your Applications folder and opens it. You can close Terminal.
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Click Install Stems Cache, Install Demucs v4, or both, one after the other (after Continue on the welcome message), and Install to confirm each. If a button is greyed out, the line under the buttons says why (see Troubleshooting).
- Demucs v4 downloads the model (about 300 MB) and puts it in place. No password.
- Stems Cache needs your password and, the first time, macOS's permission (steps 4 and 5).
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Type your password when it asks (Password needed), then click Continue.
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The first time only, allow RB Stems Plus in macOS. macOS says "RB Stems Plus was prevented from modifying apps", and the app shows you these steps:
- In the notification, click Allow.
- Turn on RB Stems Plus in the list, then confirm.
- When macOS offers to quit and reopen RB Stems Plus, choose Later.
- Back in RB Stems Plus, click Try Again.
Installing Stems Cache takes about a minute. When the light of what you installed is green, you're done.
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Open rekordbox, load a track and turn on STEMS. With Demucs v4 the first time takes longer than before. Load it again later: with Stems Cache it's much faster.
Changed your mind? Each feature can be added or removed on its own any time.
- A notice that "RB Stems Plus Watcher" can run in the background. That's RB Stems Plus's small helper that tells you when a rekordbox update needs a reinstall. It only asks, it never changes anything by itself.
- With Stems Cache, at every rekordbox update: macOS says "rekordbox was prevented from modifying apps". Click Allow so the update can finish. This is expected: Stems Cache re-signs rekordbox on your Mac, so macOS asks before Pioneer's updater replaces it.
- macOS asks again for RB Stems Plus after RB Stems Plus updates itself, the next time it installs, reinstalls or removes Stems Cache. Same steps as above.
- Sometimes macOS doesn't ask at all, for example right after rekordbox was installed or updated. That's normal.
The two lights at the top show each feature: a green check means it's on, a red cross means it's off. Stems Cache's light turns yellow when it's installed but not saving stems right now, for example when the disk is low or rekordbox has a STEMS Engine that Stems Cache doesn't support yet: hold the pointer over it to see why. Anything that can't be installed is explained in the line under the buttons.
- A rekordbox update puts Pioneer's original rekordbox back, so Stems Cache is off until you reinstall it. Demucs v4 keeps working, and your saved stems are kept.
- A new STEMS Engine puts rekordbox's own model back, so Demucs v4 is off. Stems Cache goes on saving stems if it supports that STEMS Engine; if not yet, its light turns yellow until an RB Stems Plus update does.
When the update is done and rekordbox is closed, RB Stems Plus asks: Reinstall Now, Remind Me Later or Don't Ask Again for This Version. Reinstall Now opens the app and reinstalls only what went missing. Or open the app any time and click Reinstall.
If RB Stems Plus doesn't support the new version yet, it says so instead, checks again each time you open it, and asks you to reinstall once it can.
When you open it, RB Stems Plus checks (at most once a day) for a newer version. If there is one, the line under the buttons says "RB Stems Plus X is available", and Update RB Stems Plus appears in the RB Stems Plus menu. The new version replaces the old one in one step. If the update can't finish, RB Stems Plus stays as it was and tells you why the next time it opens.
RB Stems Plus › Settings… (Cmd+,) sets how much space saved stems may use (20 GB by default) and after how many days unused stems are removed (60 by default). They apply the next time rekordbox opens. Clear Saved Stems frees the space now.
Open RB Stems Plus and click:
- Uninstall Stems Cache: rekordbox gets Pioneer's original files back, byte for byte.
- Uninstall Demucs v4: rekordbox gets its own stems model back. Stems Cache, if you have it, goes on saving stems with that model.
- Uninstall RB Stems Plus Completely: rekordbox goes back to exactly how it was, and RB Stems Plus deletes itself, its settings, its logs and the stems it saved.
Your music and your rekordbox library are never touched. The complete uninstall ends with this:
- It's unofficial. AlphaTheta doesn't know about it or support it. A future rekordbox could change how STEMS works. RB Stems Plus then leaves rekordbox on its own model until it's updated.
- It changes rekordbox's files. Demucs v4 replaces rekordbox's model file. Stems Cache replaces one file inside rekordbox.app and re-signs the app on your Mac, so while it's installed rekordbox is no longer signed by AlphaTheta. Pioneer's originals are kept, and uninstalling puts everything back. Reinstalling rekordbox from rekordbox.com also always gives you Pioneer's app.
- rekordbox's licence (EULA) doesn't allow modifying the program. Stems Cache clearly does, and swapping the model arguably does too. In our tests rekordbox sent nothing about it, but we can't promise that stays true. If you contact AlphaTheta support, uninstall first.
- No warranty. It's free software under the MIT licence, provided as is. Tested with rekordbox 7.2.17 to 7.2.19 on macOS 26 Tahoe on an Apple Silicon Mac.
- Never try new software for the first time at a gig.
- Nothing is sent anywhere. No tracking, no accounts. RB Stems Plus only goes online to download its own files from this project's GitHub Releases.
- Releases are signed. Each release comes with a signed list of its files. The install command and the app check that signature, and each file's checksum (a fingerprint of the file), before using anything.
- Logs stay on your Mac (
~/Library/Logs/rbstemsplus). They never contain your audio or track names. - A problem report is never sent automatically. You make it and attach it yourself (see Get help).
Is it free? What's the catch? Free and open source (MIT licence). The catch is in Honest risks: it's unofficial, and Stems Cache changes one file in rekordbox.
Is it safe to paste a command into Terminal? The line downloads a short script from this project's GitHub Releases. It checks every file against the release's signed list before it puts the app in Applications. You can read it first.
Why a command instead of a normal download? Apps downloaded in a browser from developers without a paid Apple account trigger macOS's "damaged" or "unidentified developer" warnings. The command avoids them.
Will it break rekordbox? Demucs v4 swaps only the model file. Stems Cache replaces one file inside rekordbox and keeps Pioneer's original, which uninstalling puts back. If anything goes wrong, reinstalling rekordbox from rekordbox.com gives you Pioneer's app again.
Will it touch my library, playlists, cues or music? No. It never opens them, and uninstalling doesn't touch them either.
Is it allowed? Can AlphaTheta ban my account? It unlocks nothing you don't already have. But rekordbox's licence doesn't allow modifying the program, and Stems Cache does. In our tests rekordbox sent nothing about it. See Honest risks.
Which rekordbox plan do I need? One rule answers this and the next few questions: if STEMS works in your rekordbox, RB Stems Plus works with it. If it doesn't, RB Stems Plus can't add it.
Does it work with my controller, CDJs or USB exports? RB Stems Plus only changes the separation done inside rekordbox on your Mac. A controller just controls rekordbox, so it gets the Demucs v4 stems. It doesn't touch USB exports, CDJs or any other hardware.
Does it work with streaming tracks? No. rekordbox doesn't separate streaming tracks, so STEMS, and RB Stems Plus with it, works only on tracks you have as files.
Which rekordbox versions work? rekordbox 7. Demucs v4 works with the STEMS Engine versions RB Stems Plus knows; Stems Cache only with the rekordbox versions it was tested on (7.2.17 to 7.2.19 at release). The list is updated online, and the app tells you if your version isn't on it yet.
Which Macs? Windows? Mac only. Tested on macOS 26 Tahoe on an Apple Silicon Mac.
Do I need both features? No. Each works on its own: Demucs v4 changes the model, Stems Cache saves the stems of whichever model rekordbox uses. Install one, both, or add the other later.
Will my tracks sound better? It depends on your music: see Which model sounds better?. If you prefer rekordbox's model, Uninstall Demucs v4 brings it back any time.
Does it work offline, at a gig? Yes. Separating tracks and loading saved stems happen on your Mac, with no internet needed (we tested it with the network off). Installing needs internet. Reinstalling works offline from the files already on your Mac (for Stems Cache, only if they were downloaded in the last 7 days).
Can I prepare my tracks before a gig? Load each track once with STEMS on and let rekordbox separate it: Stems Cache saves the stems. Stems unused for 60 days are removed, which you can change in Settings.
Do saved stems survive restarts, updates, renaming or moving tracks? Yes. They stay until the size limit, the day limit or Clear Saved Stems removes them. They're found by the audio itself, so renaming, re-tagging or moving a track (or the whole drive) doesn't matter. After a rekordbox update, reinstall Stems Cache to use them again. Stems saved with one model are used only with that model: switch back and they load again.
Does it change BPM, key, waveforms or analysis? No. Only the stems model changes. Everything else rekordbox does runs on its own files, unchanged.
Does the app need to stay open? No. Its small helper, RB Stems Plus Watcher, runs in the background and asks you to reinstall after a rekordbox update. If you turn it off (System Settings › General › Login Items & Extensions), the app says "Reinstall reminders are off": then open it after rekordbox updates.
Do I have to reinstall after every rekordbox update? For Stems Cache, yes: RB Stems Plus asks when the update is done (one click). Demucs v4 survives rekordbox updates, but not a new STEMS Engine download.
Can I change how much space saved stems use? Yes, in Settings. The stems are in
~/Library/Caches/rbstemsplus. Don't move that folder or replace it with a link.
Something's wrong. See Troubleshooting, also in the app under Help › RB Stems Plus Troubleshooting.
Help happens in this project's GitHub issues. You need a free GitHub account.
- In RB Stems Plus, choose Help › Create Report. It saves a zip on your Desktop.
- Click Open GitHub Issue. Your browser opens a new issue with the technical details already filled in, and Finder shows the zip.
- Write what happened under What happened?, drag the zip into the issue, and submit it.
The report holds RB Stems Plus's logs and settings, the versions of macOS, rekordbox and RB Stems Plus, and rekordbox's recent errors and crash reports. It never includes your library, your music or track names, and your user name is replaced. More in Making a problem report.
Made by Gabe-LS. MIT licence, see LICENSE. The Demucs v4 model is Meta's htdemucs (MIT). Stems Cache includes libFLAC (BSD-3-Clause) and uses rekordbox's own ONNX Runtime. Full credits in NOTICE.
rekordbox, Pioneer DJ and AlphaTheta are trademarks of AlphaTheta Corporation. RB Stems Plus is not made, endorsed or supported by AlphaTheta or Pioneer DJ.