Count the bars — exact, and free
A drum loop that actually loops gives you an exact tempo with arithmetic. No tool required.
BPM = (beats in the loop × 60) ÷ length in secondsIn 4/4: 1 bar = 4 beats, 2 bars = 8, 4 bars = 16, 8 bars = 32.
A 2-bar loop that is 3.75 seconds long:
(8 × 60) ÷ 3.75 = 128 BPMFor a well-cut loop this beats every detector, because the precision is limited only by how accurately the file was trimmed.
Where it breaks: reverb spilling past the loop point, or a trim a few milliseconds short. If you get 127.4 in a pack where everything else is 128, trust 128 — that is a trim artefact, not a tempo.
Get the exact length
Rounded durations are the enemy. "3.7 seconds" is not enough precision.
- In your DAW: switch the ruler to samples or time and read the region length.
seconds = samples ÷ sample rate. - In an analyser: DropWave reports the length beside the tempo, so you can cross-check its number against your own arithmetic on the same screen.
Half or double: the real question
Drum loops are where metrical confusion happens most, because a drum pattern is periodic at several levels at once and all of them are real.
The clues:
- Where does the kick land? In most four-to-the-floor material it is on every beat. If your candidate tempo puts it on every other beat, you are at half time.
- Where does the snare land? Beats 2 and 4 is the default. If your candidate puts snares on 1 and 3, halve or double it.
- What is the hat subdivision? Hats on eighths at 140 are the same audio as hats on sixteenths at 70.
- Does it match the genre? House 120–130, techno 130–150, hip-hop 80–100, trap 130–150 written (often felt at 65–75), drum & bass 165–175, footwork around 160. Convention is not a rule, but a house loop coming back at 65 is a metrical level, not a discovery.
Use a detector for the first pass
Counting bars is exact but manual. For a folder of two hundred loops, analyse first and verify the odd ones.
DropWave reports tempo to two decimal places and names the other metrical level when both fit — "could also be 206.32 BPM" — which on a drum loop is exactly the information you want, because it tells you both grids are real.
It reads the pulse from across the spectrum rather than the low end alone, which matters specifically on drum material: a loop where the kick drops out for a bar, or a percussion loop with no kick at all, still has hats and rim clicks defining the grid.
The awkward cases
Swung and shuffled loops. Swing displaces the off-beats, so the onset spacing is uneven and both your ear and a detector can land slightly off. Count bars instead.
Breakbeats. A chopped break has hits everywhere and half-time readings are very common. Count bars.
Loops with a pickup. If the loop starts before the downbeat, the file length is not a whole number of bars and the arithmetic is wrong. Trim to the downbeat first.
One-shots and fills. Nothing periodic. There is no tempo to find.
The routine
- Analyse the folder. Note the tempos.
- Sort by BPM. Outliers stand out immediately — the loop that came back at 64 in a pack of 128s is a half-time reading, not a 64 BPM loop.
- Spot-check by counting bars on anything that looks odd.
- Rename with the tempo and key —
break_128_Am_8A.wav. It travels with the file and works in every tool.