By NaJade · DJ in Bangkok · Published October 20, 2026
This guide is part of how to learn to DJ: the complete guide.
Push the tempo fader up and the vocal shouldn’t start sounding like a chipmunk. If it does, key lock is off.
Every DJ app and every club player has a small button that changes how the tempo fader behaves. On Pioneer DJ CDJs it says MASTER TEMPO; in Serato it’s Keylock; in Traktor and Engine DJ it’s Key Lock. They all do the same thing, and understanding it explains a lot about why some mixes sound clean and others sound slightly off-key.
Key lock (Master Tempo on CDJs) keeps a track at its original pitch when you change its speed. Turn it on for most club mixing so vocals and melodies stay in key. Turn it off for vinyl-style pitch, big tempo jumps or scratching, where time-stretching artefacts become audible.
What Key Lock Actually Does
Without key lock, a digital deck behaves like a turntable: speed and pitch are tied together. Push the tempo up 6% and the track plays 6% faster and about one semitone higher. That is how vinyl has always worked, and on a small change most people never notice.
With key lock on, the software separates the two. It uses time-stretching — an audio process that changes duration without changing pitch — so the track speeds up but stays in its original key. Serato’s own documentation puts it simply: enabling Keylock means the song keeps its key when the tempo changes. The underlying technique is explained well in Wikipedia’s article on audio time stretching and pitch scaling.
| Platform | What it’s called | Where to find it |
|---|---|---|
| Pioneer DJ / AlphaTheta CDJs | MASTER TEMPO | Button beside the tempo fader; “MT” shows on screen |
| rekordbox | Master Tempo | Deck panel, the “MT” button |
| Serato DJ Pro | Keylock | Deck header, padlock icon |
| Traktor Pro | Key Lock | Deck key/lock controls |
| Engine DJ (Denon) | Key Lock / Key Sync | Dedicated button on PRIME and SC LIVE units |
When to Turn Key Lock On
- Mixing anything with vocals. A sped-up vocal is the first thing a crowd hears as “wrong”. Key lock keeps singers sounding like themselves.
- Melodic genres. Progressive house, melodic techno and trance live on chords and leads. Pitching a track up a semitone can make a smooth blend clash. See how to mix in key.
- Long blends. The longer two tracks play together, the more any key difference shows. Key lock keeps the key you planned for.
- Beginners learning to beatmatch. It lets you concentrate on the beat without the pitch drifting as you ride the fader. Start with the beatmatching guide.
When to Turn It Off
Key lock isn’t free. Time-stretching has to rebuild the audio in real time, and the further you move from the original tempo, the more it shows — smeared kick drums, a slightly metallic or “phasey” top end, softer transients. A common rule of thumb from DJ forums and tests is that artefacts start to creep in once you move more than about 5% away from the original BPM; the exact point depends on the software and the track.
- Big tempo jumps. Taking a 122 BPM track up to 132 is roughly 8%. Better to change tempo gradually or use a transition that hides it — see how to mix different BPMs.
- Scratching. Most scratch DJs leave it off so the platter behaves like real vinyl.
- Drum-heavy, vocal-free tracks. If there’s no melody to clash, you may prefer the punchier sound of plain pitch change.
- Deliberate pitch effects. Slowing a track down for that heavy, pitched-down sound only works with key lock off.
Key Lock vs Key Shift vs Key Sync
These three often sit next to each other, which causes confusion. Key lock holds the original key. The other two change it on purpose.
| Feature | What it does | Use it for |
|---|---|---|
| Key lock / Master Tempo | Keeps the original key while tempo changes | Everyday mixing |
| Key shift | Moves the key up or down in semitone steps | Fixing a near-miss key clash |
| Key sync | Shifts to the nearest compatible key automatically | Quick harmonic blends |
On the CDJ-3000 family, rekordbox’s own CDJ/XDJ control mapping lists Master Tempo, Key Sync and Key Shift as separate functions, and pressing Master Tempo or Key Sync again resets to the original key. Serato ties its higher-quality keylock to the Pitch ‘n Time DJ option — the Serato software overview shows where it lives. Shifting key by more than a semitone or two runs into the same artefact problem as big tempo changes, so use it lightly.
A Simple Workflow That Works
- Turn key lock on by default in your software preferences, and on each CDJ when you start your set — club players are often left with it off.
- Keep tempo changes small. Plan your set so neighbouring tracks are within a few BPM of each other.
- Check the key display. If key lock is on, the key shown is the key you’ll hear.
- Listen on headphones before the blend. If the incoming track sounds grainy, bring it closer to its original tempo.
- Don’t rely on sync to hide it. Sync matches tempo; it does nothing about key.
If you’re using CDJs, the full layout is covered in how to use CDJs.
A Note From NaJade
I play a lot of progressive house in Bangkok, and it’s unforgiving with key. Early on I couldn’t work out why some blends felt slightly sour even when the beats were locked. Half the time it was a player in the booth with Master Tempo switched off — the previous DJ had left it that way, and I’d nudged the track up two or three percent. Now pressing MT is part of my plug-in routine, right after checking the USB loaded. The other half was me pushing tracks too far from their original tempo and blaming the music. Key lock is brilliant, but it isn’t magic. Keep your tempo changes small and it stays invisible, which is exactly what you want.
Related: how to mix in key, mixing different BPMs, how to use CDJs, and rekordbox vs Serato.
Frequently Asked Questions
What does key lock do in DJing?
Is Master Tempo the same as key lock?
Should key lock always be on?
Does key lock reduce sound quality?
What is the difference between key lock and key sync?
Do CDJs remember Master Tempo between DJs?
About the Author
NaJade is a Bangkok-based DJ playing progressive house, melodic EDM, pop, and Thai music across clubs, rooftops, and weddings in Thailand. He teaches beatmatching and mixing to beginners both in person in Bangkok and online over Zoom. When he’s not behind the decks, he’s documenting the journey on YouTube, Instagram, and TikTok.