Stem separation is undoing a mix: starting from a single stereo file and getting its parts back one by one. Here you get four, aligned and as long as the song: vocals, drums, bass and other. Other holds everything else: guitars, keys, synths, pads and strings. Backing vocals and doubles go with the lead, because to the model they're vocals.
When it's done, the song plays already split. Tap the vocals and you hear them alone; tap Remove on the drums and you're left with the song without them. No exporting or opening your DAW just to find out whether the split works for you.
The separation is done by Demucs, Meta's source separation model, in its htdemucs version. It learned by listening to thousands of songs whose individual tracks it had, and that's how it recognises what a kick, a bass line or a vocal sounds like even when they sit on top of each other. That's why it needs a GPU: your song is uploaded, split on a server and comes back as four files. A two-and-a-half-minute song takes about half a minute.
What you upload matters. A WAV or FLAC splits better than a low-quality MP3, because lossy compression has already thrown away details the model uses to tell one part from another. And if the song is yours, the mix splits better than the master: a hard-working limiter glues the parts together.
To remove the vocals and keep the instrumental, or the other way round, to pull out the acapella and build a remix on top. To practise your instrument by taking it out of the song. To study a reference: hearing just the bass of a song you love teaches more about how the low end is shared than any explanation, which is exactly what the kick and bass guide is about. Hearing the solo vocal of a commercial production also tells you how much compression and reverb it really carries, as the vocal mixing guide explains.
And to rescue a song of your own whose multitracks you lost: splitting it gives you something to mix again. If you want to play with them before opening your DAW, in Mix Space you place each stem in space and hear the mix change.
No separator gives you back the original tracks, and it's worth knowing where it falls short before you use the stems. There's always some bleed: a trace of cymbals in the vocals, a little vocal in other. The densest passages can show artefacts that sound watery or metallic. The vocal's reverb and delays stay with the vocal, and anything sharing the bass range, like a long 808 or a very low synth, sometimes gets split between the two stems.
How to get the best possible stems and what to do with them in your DAW is covered in the guide to separating stems from a song. And if you mix with them again, the mix analyzer tells you how the balance sits against your genre.
Yes, and without signing up: upload your song and hear 30 seconds of each stem, with solo and remove. With Pro you split the whole song, download the four stems as 24-bit WAV and split up to 20 songs a month.
Yes. Tap Remove on the vocals and you hear the backing without them: drums, bass and other together. With Pro you download those stems and sum them in your DAW for the instrumental, or download just the vocals if what you want is the acapella.
WAV, AIFF, FLAC, MP3, M4A and OGG, up to 7 minutes long. Before uploading, your browser turns it into lossless FLAC at 44.1 kHz, the rate the model works at, so a big WAV doesn't take longer to split.
Splitting it needs a server with a GPU: it's uploaded to our storage and separated by Replicate, in the United States. Only you can open it, from your account or from the browser you uploaded it with; we don't use it for anything else, and the song and its stems are deleted automatically after 30 days.
To the model, the vocal's reverb and delay are part of the vocal, so they stay with it. And in the densest moments of a mix there's always some bleed, like a trace of cymbals in the vocal. For practising, studying a mix or a home remix it's usually enough; for a commercial release, the original multitracks are still the ideal.
Splitting a song privately to study it, play along or learn how it's mixed isn't the same as publishing it. To release a remix, a sample or an instrumental of someone else's song you need the rights to that recording. With your own songs there's no such problem.