If you’ve spent any time with a stem splitter, you’ve probably noticed that some tools offer 4-stem separation and others advertise 6 or more. It sounds like more is better. It usually isn’t, at least not for most people.
Here’s what each actually gives you, and when you’d genuinely reach for one over the other.
What the stem count actually refers to
Stem count is just how many separate audio outputs the model produces from a single mixed track. A 4-stem model splits the audio into 4 files. A 6-stem model splits it into 6. Tools like Demucs, the open-source model from Meta AI Research, support both configurations and are worth knowing about even if you use an online tool built on top of them.
That sounds obvious, but the important thing to understand is that more stems doesn’t mean the model is more capable overall. It means the model has been trained to identify and separate more specific sources. That added specificity comes with trade-offs, which we’ll get to.
The underlying AI process is the same regardless of stem count – the field of stem separation frames it as estimating the probability that a given sound belongs to a given source, and that calculation happens for each output the model was trained to produce. More outputs means more competing estimates, which means more room for errors.
The standard 4-stem breakdown
A 4-stem separation gives you: vocals, drums, bass, and other.
Vocals and drums are self-explanatory. Bass covers the low-frequency melodic content, typically bass guitar or synth bass. The “other” category is where it gets interesting.
“Other” is a catch-all for everything that isn’t vocals, drums, or bass. That means guitars, piano, synths, strings, horns, sound design, pads, keys, and anything else in the mix. It all gets collapsed into a single stem.
For a lot of use cases, that’s fine. If you’re making a karaoke track, you need the vocal stem. If you’re sampling a break, you need the drum stem. The “other” stem might not matter to you at all, and even when it does, a lot of mixed-down arrangements actually blend those non-rhythmic, non-bass elements in a way that sounds coherent as a single file.
The complete guide to stem splitting covers how these stems get used across different workflows, if you want a broader picture.
What 6-stem adds
6-stem (and beyond) pulls specific instruments out of that “other” category and gives them their own output. Common additions are guitar and piano. Some tools go further and also separate synths, strings, or other labeled categories.
So instead of one “other” stem containing guitar, piano, and synths together, you’d get a guitar stem, a piano stem, and whatever’s left.
That’s genuinely useful in specific situations. The honest trade-off: more stems means the model has to make harder decisions. The artifacts and bleed that come with any separation get more pronounced when you’re asking the model to distinguish between a piano and a guitar playing in overlapping frequency ranges. A strummed acoustic guitar and a piano chord voiced in the same octave are not obviously different things to an AI model trained on audio alone.
In practice, the vocal and drum stems from a 6-stem model are often just as clean as from a 4-stem model. But the guitar and piano stems, specifically, tend to have more leakage between them. You’ll pull out what’s labeled “guitar” and hear some piano, and vice versa.
That’s not a flaw in any particular tool, it’s a fundamental challenge of the task.
When 4-stem is genuinely enough
Most remixing workflows don’t need individual instrument stems. If you’re building an acapella for a remix, you need the vocal stem from a 4-stem model. If you’re pulling drums for a new beat, same story. If you’re making a karaoke version, isolating the vocal cleanly matters far more than what happens to the instrumental.
Sampling falls into this category too. You want the drum break, you want the bass loop, maybe you want the “other” stem to chop something off the top. All of that is 4-stem territory.
Beat production, practice tracks, quick remix sketches — start with 4-stem. It’s faster, the quality is generally higher per stem, and you probably don’t need to isolate a piano anyway.
When you actually need 6
Two scenarios where the extra stems are worth it:
Learning a specific instrument. If you’re trying to transcribe a piano part, or learn a guitar riff by ear, having that instrument isolated even with some light bleed is far better than having it buried in the “other” stem with everything else. The isolation doesn’t have to be perfect to be useful for learning purposes. Drum extraction for transcription is a similar case.
Heavy post-production. If you’re doing restoration work on a track and need to process individual instruments separately, 6-stem gives you more surgical control. A session musician overdubbing on a specific instrument, a producer replacing a piano sample with a live recording, someone re-amping a guitar stem — these are the real 6-stem use cases.
For anything else, the added complexity and the quality cost usually aren’t worth it.
The honest take
Start with 4-stem. Most of the time, it’ll do exactly what you need, and the per-stem quality will be noticeably better than what you’d get from a 6-stem model under the same processing conditions.
If you find yourself specifically needing to work with guitar or piano as separate elements, then run the 6-stem version and manage the bleed from there. But don’t reach for 6-stem by default just because it sounds more thorough. More separation categories isn’t the same as better separation quality.