Stems vs Parts: What’s the difference?

If a mix engineer as decorated as Bob Clearmountain is still having to say this out loud, you know it's a genuinely widespread mix-up, not just a pet peeve of mine. Bob posted about this a while back, visibly a bit exasperated, and a fair few of the industry's heaviest hitters piled on in agreement (CLA/Scheps). The distinction he was drawing is simple:

• Multi-track parts are the individual channels that make up a session.

• Stems are those channels sub-mixed down into groups that sum to make the mix.

One is the raw ingredients. The other is a partially cooked dish. Every few months a client emails me and discusses mixing stems, we agree a rate and timeframe that suits us both. What turns up is a Zip file with forty-something individual tracks; kick, snare, a few hat tracks, three synths playing the same part, two basses, lead vocal, fourteen backing vocal takes, FX sweeps, the lot. That's not stems. That's the multi-track parts.

A mix may only bare 8-15 stems in total. Drum stem, perc stem, bass stem, brass stem, string stem, 2 synth stems, 2 guitar stems, ld vox stem, bvox stem.

Why the confusion actually costs you

This isn't pedantry for its own sake. If a client thinks they've sent you stems but they've actually sent you the parts, or vice versa, you can lose time on a project before anyone's even hit play. The parts need full mixing decisions, panning, EQ, dynamics, the works. A stem arrives with a lot of those decisions already baked in; you're now blending pre-cooked elements rather than building a mix from scratch. Confuse the two and the mixer may have to do far more work than the brief called for thus pushing your budget up. Bob's point wasn't "know your jargon for the sake of it", it was "get this wrong and it slows the whole session down."

Stems are great

What I love about stems is the in ability to change the vibe of what the producer is going for. I was mixing a 70s soul inspired track and just had no chance of recreating the drum sound the producer had, I didn’t have a clue what they’d done but it sounded great. Instead of convincing the client my version was cleaner or more dynamic, I had the drum stem sent over and worked from that and didn’t need to touch it at all. Using a bvox stem can save hours of EQ’ing, fading and automation riding or an FX stem with baked in delays can maintain the producers intention instead of sifting through a bunch of tracks trying to figure out why they don’t sound like the rough mix.

The takeaway

If you're a producer, artist, or student sending work to a mixer:

• Multi-track parts - Every individual channel, unprocessed or close to it. Send this if you want someone to build the mix from the ground up.

• Stems - Grouped, sub-mixed audio, such as drums, vocals group, brass section, whatever the split, a stereo file. Send this if the balance is largely set and you need it to remain that way, great for time saving on the mix or straight to mastering.

Get the terminology right with who ever you're working with before you export the session. It's a two-minute conversation. Bob's been doing this since the seventies and he still thinks it's worth saying clearly, which tells you it's not a small thing.