Key and BPM Finder

How to use it

1. Drop a finished track, a stem or a loop onto the panel, or press it to choose a file. Anything from a few seconds to 12 minutes works.
2. Read the key and tempo. If the confidence is moderate or low, the two closest alternatives are listed; check them against the song by ear.
3. Click the key, Camelot code or tempo to copy it for your DAW, sampler or DJ software.

For the key, material with chords or a bass line reads best. A drum loop on its own has a tempo but usually no key, and the finder says so rather than guessing.

Reading the result

• Key and confidence. The confidence is the share of the evidence the winning key takes from all 24, scaled down when the best match is weak, when there is little sustained pitched sound (noise and drums give no key at all), and when there are only a few seconds of it. High means one key clearly fits; low means several fit about equally, which is common for loops that never resolve. A single held chord tops out at Moderate, because one chord fits several keys, and with no third above the root the finder names the root and leaves major or minor open.
• Relative key. Every major key shares its notes with a minor key three semitones below (C major and A minor). Producers often need both: samples tagged in one work in the other.
• Tuning. The reference the track is tuned to, as A4 in hertz. Most music sits within a few cents of 440 Hz. If yours reads 432 or 445, set your synths or the note converter to match before tuning an 808.
• Pitch-class profile. How much of each note the track contains. The notes of the detected key are lit, so you can see why it was chosen.

Half time and double time

Tempo detectors disagree with each other most often by a factor of two, because a groove has a pulse at several levels at once: the kick, the snare backbeat and the hi-hats. This finder reports a tempo between 70 and 180 BPM and always shows the half-time and double-time values next to it. Trap is usually counted at 130 to 150 BPM even though it feels half as fast, and drum and bass at around 170 to 176 BPM with a half-time feel near 87. Use the one your genre and DAW grid expect.

Mixing with Camelot codes

The Camelot wheel arranges the 24 keys so that neighbours share all but one note. From any code, three moves stay in key: one step clockwise (a fifth up, 8A to 9A), one step anticlockwise (8A to 7A), and the same number with the other letter (8A to 8B, the relative major). Moving two or more steps, or jumping across the wheel, is an energy change that works best on a breakdown.

How it works and how accurate it is

Key. The audio is folded to mono and resampled to about 11 kHz. Roughly every fifth of a second, a window of about 0.7 seconds is searched for tonal peaks between 50 Hz and 5 kHz that stand out from the noise around them. The tuning is estimated from those peaks, each peak is assigned to its note with its overtones pointed back to the fundamental, and the twelve note totals are correlated with the Krumhansl-Kessler major and minor key profiles in all 24 keys.

We chose Krumhansl-Kessler after testing three published profile sets on synthesized triads, cadences and pop progressions in every key. Temperley's classical profiles missed nearly every natural-minor loop (the i, VI, VII progression behind much of modern pop and hip-hop), reading them as the relative major. EDMA profiles, built from electronic dance music, came close but lost more short loops and bright synth tones.

On that test set (all 24 keys, tuned 30 cents flat, in tune and 30 cents sharp, clean, with noise as loud as the music, and with drums), it named 862 of 864 keys exactly at 22.05 and 44.1 kHz and 863 of 864 at 48 kHz. Triads, cadences and minor loops were right every time. The misses were the I, V, vi, IV pop loop with drums, read as its relative minor with the right key listed as the alternative. Real recordings are harder than synthesized ones: modal songs, key changes and loops that never land on the home chord can all read as a neighbouring key, which is why the confidence and alternatives are shown.

Tempo. An onset envelope is built from rises in energy across twelve frequency bands, so the kick and snare count as much as the hi-hats. Its autocorrelation is scored at one, two, three and four beats, because a real beat repeats at every multiple. On twelve synthesized genre patterns from 70 to 172 BPM it never picked a tempo outside the true value, its half or its double.

Common mistakes

• Analyzing a drum loop for its key. Drums are mostly noise. Use a chord, bass or melody stem for the key and the drums for the tempo.
• Trusting a low-confidence key. When the top keys are close, play the alternatives against the track. The one whose root chord sounds like home is the key.
• Ignoring the tuning. A sample tuned 30 cents sharp sounds out against an 808 tuned to 440 even when the key is right.
• Mixing up relative keys. A minor and C major share their notes but not their home chord. For harmonic mixing either works; for writing a bass line, the tonic matters.