DJ BPM & Key Detection from Audio
You can hand the SoundStash planner an audio file and get a tempo estimate, a Camelot key and the track length back in a few seconds — without the file ever leaving your computer. Here is exactly how it works, and where it gets things wrong.
Updated September 2026 · 7 min read · SoundStash editorial
What the analyser actually does
In the DJ Set Planner there is a button labelled Add track from audio. Pick an MP3, WAV, M4A, AAC or FLAC file and the planner decodes it, estimates the tempo, takes a guess at the key, reads the duration, and appends a new row to your set with those fields already filled in.
Everything after that is normal planner behaviour: the row is fully editable, the energy arc and harmonic flow update live, and the track counts towards clash detection and transition tips like any track you typed in by hand.
Your file is analysed in the browser, not uploaded
This matters if you work with promos, unreleased edits or client stems. The analysis runs with the Web Audio API inside the page you already have open. The audio is decoded in memory on your own device — it is not sent to SoundStash, not stored in our database, and not passed to any third party. Only the three small values you can see afterwards (BPM, key, length) ever exist as data, and they only exist in your set.
The practical consequence: a long lossless file takes a moment to decode, and very large files can be heavy on an older laptop. If a file fails, the planner tells you and you can still add the track manually.
How accurate is it?
Be sceptical, in a specific way. Tempo detection on four-to-the-floor material is generally reliable. Key detection is genuinely hard, and no analyser — ours, Rekordbox, Serato or Mixed In Key — agrees with the others all of the time.
BPM: usually right, sometimes doubled or halved
The classic failure is the octave error: a 174 BPM drum & bass roller reported as 87, or a 70 BPM halftime dubstep tune reported as 140. Both numbers describe the same groove, so glance at the value and double or halve it if it is not what you count. Live recordings, heavily swung material and intros with no drums are the other weak spots.
Key: treat it as a starting point
A detected key can land a fifth away, or on the relative major instead of the minor. If two tracks are supposed to blend for 32 bars and the planner says they clash, trust your ears first. Fix the field and the harmonic map redraws instantly. The logic behind those relationships is in our Camelot wheel harmonic mixing guide.
What we will not pretend
This is an estimate designed to save you typing, not a replacement for the analysis in your DJ software. Before you play out, the values in Rekordbox or Serato are the ones that count — use the planner to decide the shape of the set, not to grid your tracks.
Free limits and Pro
Auto-analyse is free: three files a day, per browser, resetting at midnight UTC. That is enough to fill in the tracks you cannot remember the numbers for. Pro removes the daily cap entirely and adds unlimited saved sets, PDF set sheets and Rekordbox XML export. Nothing else about the planner is gated — the arc, the Camelot map, clash detection and shareable links are free forever.
A workflow that actually saves time
Analysing 30 files one at a time is not the point. The useful pattern is: sketch the set shape first, then analyse only the handful of tracks whose numbers you are unsure about.
Decide your closer and your peak, block out warm-up, build, peak and descent, then start filling rows. When you hit a track you have not played for months, hand the file to the analyser instead of digging for the numbers. The full method is in how to plan a DJ set.
Then check the key values on anything you intend to long-blend, correct the two or three the analyser got wrong, and export. Five minutes of checking is worth more than any detection algorithm.
Judge the result on decent monitoring
Deciding whether a detected key is right is a listening job, and laptop speakers will not help you. Closed-back headphones with a flat-ish response are the cheapest upgrade to your decisions: our DJ headphones comparison covers the three standards side by side. If you are also choosing hardware to rehearse the set on, the DJ controller comparison is the companion piece.
Try it on one track
Open the planner, hit Add track from audio and give it something you know the tempo and key of. You will learn more about how far to trust it from one familiar record than from any accuracy claim we could make here.