Tempo & rhythm
Pitch vs tempo
Tempo is how fast a track plays; pitch is how high it sounds. On a turntable they are one control, because speeding a record up raises its pitch. Digitally they can be separated, which is what key lock does.
In practice
Coupled, tempo drags pitch with it. Key lock separates them and charges you artefacts for the privilege.
Under about three per cent, leave key lock off — the pitch shift is small, it often sounds better than the processing, and the key change is usually musically harmless. Above that, turn it on, because the key drift starts to matter more than the artefacts. And remember the two names describe the same fader: a DJ saying "pitch it up two" and a display reading a tempo change are talking about one movement, which is worth knowing before someone says it to you in a booth.
±3%
Below this, leave key lock off
1 fader
What both words describe
Artefacts
What separating them costs
Where these come from: Working thresholds for key lock in DJ use and the mechanical coupling on vinyl — practice, not catalog figures. For what we can measure, see the control that separates them.
Why it matters
The coupling is why the control on a deck is called a pitch fader while the number it changes is a tempo. On vinyl there was no distinction to make — the record turned faster and everything went up with it — and the vocabulary never caught up with the technology that separated them.
The practical consequence is a choice you make every time you move the fader more than a little. Leave them coupled and a big tempo change moves the key, which may be exactly what you want harmonically. Separate them with key lock and the key holds, at the cost of processing artefacts that grow with the size of the change.
Frequently asked
Why is it called a pitch fader if it changes tempo?+
Because on a turntable they are the same thing — the record turns faster and everything rises with it. The name survived the technology that separated them.
Should I always use key lock?+
Not below about three per cent, where the pitch shift is small and often preferable to the processing. Above that the key drift matters more than the artefacts.
Does changing tempo change the key?+
With key lock off, yes — proportionally. That is sometimes useful harmonically, which is why leaving it off on small changes is a real choice rather than laziness.
Related terms
Pitch fader
The pitch fader is the slider that speeds a track up or slows it down, usually by up to 6 or 8 percent. It is how two records are brought to the same tempo before they are mixed.
Key lock
Key lock — master tempo on a CDJ — holds a track at its original pitch while you change its tempo. Without it, speeding a record up raises its key and quietly undoes whatever harmonic mixing you had planned.
BPM
BPM — beats per minute — counts how many beats land in sixty seconds. It is the first number a DJ checks, because two tracks have to agree on tempo before anything else about them matters.
Key sync
Key sync shifts a track’s pitch so its detected key matches another track’s, independently of tempo. It is not key lock: key lock preserves pitch while tempo changes, key sync deliberately changes pitch.
Explore: Pitch and tempo calculator · Pitch fader · Key lock · All DJ terms