Tempo & rhythm
Half-time vs double-time
Half-time keeps the tempo and moves the drums to half the rate, so the track feels slower without being slower. Double-time does the reverse. Neither changes the BPM — both change what the BPM feels like.
In practice
Both are a drum feel at a fixed tempo. That is why 174 and 87 mix, and why detectors read one as the other.
Use the relationship deliberately: a half-time section is how a track drops in intensity without losing the grid, and switching between a half-time record and a straight one at the same BPM is a large change in feel from a transition that is technically trivial. In your library, expect the detector to have made this choice for you and check the extremes of your BPM sort — a cluster of drum and bass in the eighties is this ambiguity, not a genre of slow records.
Same BPM
What neither changes
174 / 87
The pair that feels identical
Sort by BPM
How to find the errors
Where these come from: The tempo relationship itself. The measured share of the catalog affected by half-time detection is on the linked article. For what we can measure, see the half-time correction, measured.
Why it matters
The reason this matters for mixing is that two tracks at the same BPM can feel like completely different tempos, and two at half and double can feel identical. A 174 BPM track with half-time drums sits comfortably against 87, which is why the pairing works and why detection software gets confused by it.
It is also the single most common source of a wrong BPM in a library. A detector looking at a half-time drum pattern will often report half the playing tempo, and it is not exactly wrong — the pulse it found is real, it is just not the one the record is played at.
Frequently asked
Can you mix a 174 BPM track with an 87 BPM one?+
Yes, and it is a standard move — one beat of the slower track lines up with two of the faster one, so the grids agree even though the numbers look far apart.
Why does my library have drum and bass at 87 BPM?+
The detector found the half-time pulse, which explains the record perfectly well mathematically. Doubling the tempo and re-gridding fixes it.
Does half-time change the tempo?+
No. The BPM stays exactly the same and only the drum pattern changes rate, which is why it feels slower without any grid or pitch change.
Related terms
Half-time
Half-time is a groove that feels half as fast as it counts — the snare lands every other bar instead of every other beat. Drum & bass written at 174 BPM is felt, and often detected, at 87.
Double-time
Double-time is the mirror of half-time: a groove counted at one tempo and felt at twice the rate. A 70 BPM beat played as 140 is the same record, counted differently, and mixes on the same grid.
BPM detection
BPM detection finds the repeating pulse in a track by measuring where energy rises and looking for the interval that best explains those onsets. It returns a tempo and a grid, and both can be right about the wrong thing.
Beat vs bar
A beat is one pulse; a bar is a group of them, four in almost all club music. Tempo is counted in beats and structure in bars, which is why DJs use one for matching and the other for planning.
Explore: Half-time and double-time · Half-time · Double-time · All DJ terms