Rhythm, meter and groove

Some beats make your head nod before you've decided anything. Others, with exactly the same drums on exactly the same beats, just sit there. The difference is often a few hundredths of a second, and it isn't random.

Here's a plain drum line: kick, hi-hat, snare, hi-hat. Press play and let it loop for a bar or two.

Before you move Swing: when the hi-hats start arriving late, will the whole beat feel slower, or will something else happen? Then raise it slowly and listen for the moment it starts to lean.

What just happened

The kick and snare didn't move. Watch the piano roll: only the hits between the beats slid to the right. Each beat still starts exactly on time, so the tempo didn't change at all. What changed is how the two halves of each beat share their time. The first half got longer, the second got shorter. Long, short. Long, short.

That's swing: pairs of subdivisions played long-short instead of even.

• Pulse is the steady beat you tap your foot to.
• Subdivision splits each beat into smaller, even slots: two per beat (eighths), four (sixteenths) or three (triplets).
• Tempo is how fast the pulse goes, in beats per minute. At 96 BPM, one beat lasts 625 ms.

Swing keeps the pulse and bends the subdivision. In the lab's drum line, the low C is the kick, D is the snare and F♯ is the closed hi-hat, the usual drum-machine note map.

How much swing?

The Swing control counts where the off-beat lands, as a percentage of the beat. 50% is dead even. 67% puts it two thirds of the way through, which splits the beat into a triplet's long-short (2:1). Anything in between is a lighter lean.

These numbers come straight from drum machines. Roger Linn's machines, and the Akai MPCs he designed, offered swing as exactly this kind of percentage, and a lot of hip-hop and house lives in the low 50s and 60s, where the beat leans without fully skipping. Jazz drummers don't think in percentages at all. Their swing ratio changes with tempo: tighter and closer to even at fast tempos, looser and more lopsided at slow ones. A number is a starting point, not a style.

Try 54%, then 58%, then 62%. You'll probably find a point where the hats stop sounding late and start sounding relaxed. That spot depends on the tempo, the sounds and your taste, which is why the control is a dial and not a switch.

Why random isn't groove

A common shortcut for "make it feel human" is to nudge every hit by a random few milliseconds. Try imagining it on this beat: one hat 30 ms late, the next 5 ms, the next 40, the next on time. It's looser, but it doesn't swing, because nothing repeats. Swing works because the long-short pair comes back every beat, so your body can predict it and lean into it.

That's also what makes the most famous "off-grid" beats work. J Dilla is widely reported to have programmed with quantize switched off, so kicks and snares land slightly ahead of or behind the grid. Listen closely and the pushes and drags recur: it's a placement you can learn to feel, not noise.

Random variation still has a job. It keeps a repeated sample from sounding machine-gunned, or loosens a dense texture. Decide where the important hits go first, then add variation if it helps. Maru's Humanize adds that kind of variation; its timing nudges only ever push notes later, so put deliberate pushes ahead of the beat in the pattern itself.

Where the strong beats are

Timing is one half of groove. The other half is which hits are strong. Here are twelve identical notes. Only the accents change.

With accents on 1, 4, 7 and 10 you'll hear a rocking ONE-two-three, ONE-two-three: the swaying feel of a slow blues ballad, or a jig. Move them to every second note and the same twelve notes march in twos. Neither the notes nor the tempo changed. Your ear grouped them differently.

That grouping is meter: a recurring pattern of strong and weak beats. A time signature like 4/4 or 6/8 is one way to write it down, and a waltz's ONE-two-three is meter you can dance to. Groupings don't have to be even, either. Dave Brubeck's "Take Five" counts in five. Much Balkan dance music groups beats unevenly, such as a seven split 3+2+2, and it feels perfectly natural to the people dancing it. The Afro-Cuban tresillo splits eight subdivisions 3+3+2, and you can hear that rhythm everywhere from son and salsa to reggaeton and plenty of pop. Try it here: accent 1, 4 and 7 and listen to the first eight notes.

Software that finds the beat in a recording has to make this same grouping decision without being told, and it often settles on twice or half the tempo you feel. Beat and tempo tracking shows why both answers can be honest.

Other traditions build whole systems on this. In Hindustani music, a tala is a rhythmic cycle such as the sixteen-beat tintal. Its first beat, sam, is the strongest arrival, and musicians improvise long, elaborate phrases that land together on sam. The cycle is felt as a loop with a home, very like the way a chord progression has a home key.

Where the rule breaks

Swing depends on tempo. A 40 ms push is a big lean at 160 BPM, where each eighth note lasts 188 ms, and barely there at 70 BPM. If you change tempo a lot, retune the swing by ear.

It also depends on which subdivision you swing. Swinging sixteenths at 90 BPM gives the skippy bounce of a lot of hip-hop and UK garage; swinging eighths at the same tempo sounds closer to a shuffle. Same percentage, different feel.

And the parts have to agree, or disagree on purpose. A swung hi-hat over a dead-straight bass line can sound deliberately tense, or just sloppy. Pick which part is the anchor and let the others play around it.

Same idea, different place: a sidechain duck has a release time, and that recovery lands somewhere in the beat. Set it to recover on a swung off-beat and the whole mix breathes in the groove. See Gates, sidechain and ducking.

Make it yours

Program a two-bar hi-hat line in your own sequencer, or tap one on a table. Make a straight version and a swung version, keeping every velocity the same so you only hear the timing. Then find the swing amount where it feels best at your tempo, and add two or three accents on purpose.

Write down the swing percentage and where the accents fall. That pair of numbers is your groove, and you can drop it onto any new pattern.

Quick check

1. You delay every off-beat but keep the main beats fixed. Does the tempo change? No. The beats arrive on time, so the pulse is the same. Only the split inside each beat changes. It's tempting to think "later" means "slower", but the late notes borrow time from the gap after them.
2. A plugin adds random timing that averages 20 ms late. Has it swung your pattern? Not really. Swing is a repeating long-short pair, and random offsets don't repeat. The average can be the same while the feel is completely different.
3. A pattern sounds great swung at 90 BPM but drunk at 150. What do you try first? Pull the swing back towards 50%. At fast tempos a heavy long-short split leaves the short note almost no time, which is why drummers naturally even out their swing as the tempo rises. Swing usually needs retuning when the tempo moves a lot.

Next steps

• Go deeper: Scales, modes and tonal centers. A groove makes some beats feel like landing points. Pitches do the same: why does one note feel like home?
• Use it: Drum programming. Give each drum its own job in the groove.