Before you can build on a sample, or hand a loop to someone else, you need two numbers: how fast it is and what key it is in. Get either wrong and the new part drifts out of time or clashes with every note. The good news is that both can be found in a couple of minutes, with tools or with nothing but your ears and a keyboard.
This guide covers both routes, what to do when the answer looks wrong, and how to label the result so nobody has to work it out again.
Finding the BPM with a tool
The quickest route is to let software do it. Drop the file into the free BPM and key finder and it reads the tempo and key in your browser, without uploading the audio anywhere. Most DAWs can do the same: drag a loop onto an audio track, switch on warping or tempo detection, and the project reports what it found.
Detection works best on material with a clear, steady pulse. A drum loop or a full beat is easy. A single sustained pad, a free-time piano take or a sample that starts with a long fade-in gives the software very little to lock onto, and you may get a wrong answer or none at all. That is the tool being honest, not broken.
Two habits help whatever you use:
- Cut the sample to whole bars first. A clip that starts or ends mid-bar confuses the maths, and a clean cut makes the result easier to trust.
- Check the answer against the grid. Drop the detected tempo into your project, play the sample, and see whether the hits land on the lines for several bars in a row. If they slide, the number is off, even by a fraction.
Finding the BPM by ear
If you have no tool to hand, the oldest method still works. Play the sample and tap along on a key or the spacebar. A tap tempo does the counting for you, and tapping for ten or fifteen seconds averages out the wobble in your fingers. The BPM tapper is built for this, and if you would rather work it out yourself, how to find the BPM of a song by ear walks through it.
The by-hand method is to count the beats in a stretch of known length. Count how many beats fall in ten seconds and multiply by six. It is rough, but it usually lands within a few BPM, which is enough to narrow the field before you fine-tune against a grid.
Half-time and double-time
The most common wrong answer is not wrong at all. Plenty of tracks sit at two tempos at once. A trap beat with hi-hats rolling at 140 and a snare on the third beat of the bar feels like 70, and both numbers describe the same recording. Drill, much of modern hip-hop and a lot of dancehall do the same thing.
A detector picks whichever pulse is strongest, which may not be the one you count. So when a result looks twice or half what you expected, try the other:
- If a loop sounds slow and heavy but reads 140, it is probably a half-time groove, and 140 is the number that normally goes on it.
- If a bouncy loop reads 70, check whether your ear is really counting at 140.
- Whichever you choose, use it consistently. A producer filtering for trap loops is usually searching around 140, not 70.
BPM by genre shows where each style commonly sits, which is the fastest way to decide which reading a loop should carry. Our finder shows the half and double next to its answer for exactly this reason.
Finding the key by ear
A key is the set of notes a piece is built on, plus the note that feels like home. To find it by ear you only need an instrument, even a free on-screen keyboard.
- Play the sample and hum or play single notes until you find one that feels like the resting place, the note you could end on without it sounding unfinished. That is your candidate tonic.
- Play the third note above it, counting up four semitones for major or three for minor. Whichever sounds right against the sample tells you the mode.
- Play a few other notes from that scale. If none of them clash with the sample, the key is probably right.
Chord-heavy material is often easier. If the loop's first and last chords are the same, the key is usually named after that chord. A minor chord at the start and end points to a minor key, and a major chord to a major key. It is a rule of thumb rather than a law, but it gets you close fast.
Finding the key with a tool
Software finds a key by measuring how much of each of the twelve notes appears in the audio, then comparing that spread with the typical pattern for every major and minor key. The closest match wins. That is how the finder works, and how the key detection built into most DAWs and DJ programs works too.
It is a good method with honest limits. Drums, 808s and noise add energy that is not part of any note. A loop that moves through several chords can fit more than one key. Out-of-tune samples smear across neighbouring notes. So treat a detected key as a strong hint and confirm it by playing the root note along with the loop. If it sounds right, you are done.
Relative keys and why they confuse detectors
The most common near-miss is the relative key. A minor and C major use exactly the same seven notes, so a detector listening to a loop in one can easily rank the other first. They differ only in which note feels like home.
When the first two results are a major key and its relative minor, play the root of each against the loop. The one that sounds settled is the tonic. If both seem to work, the loop is happy in either, which is useful: a part in one will sit over a loop in the other with no clash. Compatible keys explains the relatives and the keys a fifth either side, and how the Camelot wheel numbers them.
When the key will not settle
Sometimes nothing sounds quite right. A few usual causes:
- The loop is modal. A Dorian or Phrygian loop shares its notes with a major key, so a detector will name that major or its relative minor. The notes are right even if the label is not the whole story.
- The sample is tuned off the standard pitch. Old records and tape-speed samples often sit a quarter-tone away from the keyboard. If every note sounds slightly flat or sharp against your instrument, tune your instrument to the sample, or pitch the sample to the grid.
- There is no real key. Percussion, risers and sound design may have no tonal centre. Leave the key off rather than guess.
- The key changes. A sample that modulates is two keys. Tag the one that runs longest, or the one your part will mostly sit over.
If you are still unsure after trying, say so. "Key unsure, sounds like F minor" is more useful to a collaborator than a confident wrong label.
Labelling the loop
Once you have the numbers, put them where people will see them. The simplest place is the filename, for example Dark Keys F# Minor 142 bpm.wav, which how to name loop files covers in detail. Write the tempo you would count, not the one a detector happened to pick, and use the key you confirmed by ear.
When you publish a loop on ColabLoop, ColabLoop reads the tempo and key from a filename like that, and both become filters other producers can search with. A correct label is one of the easiest ways to be found: someone with an A minor idea at 140 BPM can land on your loop, and it will fit. A wrong label does the opposite, because the collaborator finds out only after downloading.
Finally, label what you attest. Tempo and key are measurable, so a quick check with the finder and your ears is enough. Credits and splits are a different matter, and those are claims you make, not numbers a tool can confirm.