Two tracks in, one answer out. The tool checks the tempo gap against a real pitch fader, the keys against the Camelot wheel, and — the part no chart can give you — whether any DJ in a corpus of 70,000 published sets has played this exact pair back to back.
Most "will these mix" answers online are a Camelot lookup: same number, neighbour, or letter flip. That is one third of the question, and not the most important third. The checker above runs three, and weights them the way the data says DJs do.
A standard pitch fader travels ±6%. If the incoming track is inside that window you can match them and they will stay matched — matched tempos do not drift, however long the blend. Outside it you have run out of fader, and the move has to be a technique instead of a blend. The window is a percentage, not a fixed 3 BPM: 3 BPM is over half the fader's travel at 90 and under a third of it at 174. Half-time and double-time are the exception the raw number gets wrong: 140 into 70 is a 50% change on paper and lands on the beat. The checker folds those before judging.
From any Camelot code, four moves are safe: the same code, one step clockwise, one step anticlockwise, and the letter flip to the relative major or minor. The corpus adds something the wheel does not: how much each move is actually used. Same key runs at 1.9× chance, one step at 1.2×, and the relative flip at 1.0× — DJs use it exactly as often as they would if they ignored key. Two steps around the wheel is actively avoided, at 0.7×. The checker names the move and prints the lift, so "in key" is never a single green tick.
When both tracks are picked from the corpus search, the tool looks up every record DJs have been documented playing after the first one and checks whether the second is among them. A hit is the strongest answer this page can give: not "the theory says yes" but "this has been done, in this order, this many times". A miss proves nothing — most good pairs have never been written down — and the result says so rather than dressing the absence up as a verdict.
| Verdict | When | What to do |
|---|---|---|
| Blend it | Tempo inside the fader, keys compatible | Line them up and overlap as long as the arrangement allows. Keylock on if the gap is over 3 BPM. |
| Blend, keys clash | Tempo fits, keys are not compatible | Normal — this is most real transitions. Keep the overlap short, swap the bass on a phrase, and never let both melodies sit together. |
| Blend, key unknown | Tempo fits, one key missing | Trust your ears over the tag. Cue the incoming track's melodic section against the outgoing one in headphones first. |
| Half-time move | One tempo is about double the other | Treat as a blend. The beats still line up; let the room feel the tempo halve or double. |
| Not as a blend | Tempo gap beyond the fader | Cut on the drop, filter through a breakdown, loop out, or ride an echo tail. A different move, not a failed one. |
Two records in 8A at 126 BPM pass every check on this page and can still sound terrible together: two basslines fighting, two vocals overlapping, a hypnotic warm-up cut under a peak-time roller. Key and tempo are the checks a tag can answer; arrangement and energy are the ones you have to hear. What the checks buy you is a shortlist — the pairs worth putting in headphones — and a name for the technique when the pair fails one of them.
The reverse is also true. Across 200,000 measured transitions, 22% were Camelot-compatible against a chance rate of 16.7%. DJs demonstrably take key into account — and then, four times in five, play something else. They can, because a bass swap on the drop overlaps no melody, and a cut overlaps nothing at all. The full study is here →
| Gap | Share of real transitions | What it takes |
|---|---|---|
| Under 1 BPM | 26% | Nothing. Blend as long as you like. |
| 1–3 BPM | 49% cumulative | A nudge on the fader. |
| 3 BPM up to 6% | 66% cumulative | Blendable; keylock decides how long. |
| Beyond 6% | the remaining third | A technique, not a blend. |
One transition in twelve crosses a half-time or double-time boundary, which is why the checker looks for it before it judges the raw percentage. The tempo study →
Check three things in order. Tempo: the gap should sit inside about 6% of the playing track's BPM, which is what a standard pitch fader gives you. Key: the incoming track should be in the same Camelot code, one step either way, or the relative major or minor. Arrangement: two basslines or two lead vocals must not overlap. The first two can be read from the tags; the third you have to hear.
Yes, and most of the time they are. Across 200,000 transitions from published DJ sets, 78% were not harmonically compatible. A key clash only matters while both tracks are melodically audible at once, so a bass swap on the drop, a filter through a breakdown, or a cut avoids it entirely. Key is a filter for long blends, not a rule for every transition.
For tempo, slightly: the percentage is measured against the track already playing, so 124 into 128 is a 3.2% move and 128 into 124 is 3.1%. For key, no: the four safe moves are symmetric. For evidence, yes: the corpus counts ordered pairs, because a set that goes from A to B tells you nothing about whether B into A works.
What plays next · Camelot wheel · BPM transition calculator · Major vs minor keys · Mixing with vocals
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