What Sync is and how to use it correctly.

What Sync is and how to use it correctly

What Sync does exactly

Sync does not guess where the beat is: it reads the grid. Using that information, it makes two adjustments:

• Tempo. It matches playback speed so the BPM values agree.
• Beat position. It aligns both tracks’ beats, making one’s kick land with the other’s.

Together, the adjustments form the full mode. Rekordbox calls it BEAT SYNC: its official definition states that the playing track’s BPM and beat positions can automatically synchronise with the master deck’s track. Traktor’s equivalent mode is BeatSync, described in terms of tempo and phase: it maintains both at all times.

Keep that distinction—tempo and phase—clear from the outset. Matching tempo alone leaves tracks at the same speed but with displaced hits; matching phase too makes them sound “locked together”. The second component distinguishes Sync from a simple tempo adjustment and explains why an incorrectly placed grid spoils the result even with correct BPM.

Before Sync, the beatgrid

The documentation states a prerequisite before explaining the function: music files must be analysed to obtain beatgrid information. Without analysis there is no grid, and without a grid Sync has no source for beat positions.

Sync is therefore a derived function. It is not an independent programme capability; it follows from having an analysed and, especially, corrected library. Traktor documentation warns explicitly that track grids must be correctly placed for BeatSync to work.

There are two practical consequences:

• Two people using the same programme get different Sync results because one has corrected the grid and the other has not. Someone saying “Sync sounds bad” is almost always describing a grid rather than Sync.
• A displaced grid produces consistently displaced synchronisation. Tempo will be correct, phase will be wrong, and the result will sound misaligned regardless of BPM.

When starting out, the order is always analysis, grid correction, then Sync. Reversing it gives you false confidence while poorly prepared tracks accumulate.

The reference deck

Sync needs a reference point. That deck is designated with [MASTER], and rekordbox calls it the sync master.

Its documented behaviour has two rules worth knowing:

• You can transfer master status whenever you wish. Pressing [MASTER] on the other deck transfers it there.
• Master status transfers automatically in two situations: changing or unloading the master’s track transfers it to the other deck. In EXPORT mode with two players, the first to start playing becomes sync master.

That second rule explains behaviour that confuses beginners: starting the opposite deck to hear how it sounds may change the master unintentionally. If something stops sounding as expected after previewing, check master status first.

Traktor’s equivalent is the Tempo Master, with a central Master Clock coordinating deck, loop and effect tempo and synchronisation. Traktor also documents a detail that differs from rekordbox: a deck synced to a Tempo Master cannot have its tempo adjusted manually; only the master can change it. When the Tempo Master’s track ends or stops, the synced deck automatically becomes the new Tempo Master.

This distinguishes “Sync locks my tempo”—documented behaviour—from “Sync is broken”.

The official procedure

Rekordbox documents four steps, best followed in order because each depends on the preceding one:

1. Press [MASTER] in the track-information panel of the deck you want as sync master.
2. Start playing the track on the deck you will synchronise.
3. Press [BEAT SYNC] in that deck’s track-information panel.
4. To cancel, press [BEAT SYNC] again.

An often overlooked detail: with BEAT SYNC enabled in rekordbox, BPM can change to the same as, double or half the sync master’s BPM. The control is SYNC RATE, cycling x1 → x2 → x1/2. The documentation adds that if doubling tempo would exceed +100%, x2 is skipped.

SYNC RATE is useful for mixing tracks deliberately at half or double tempo, and for quickly correcting synchronisation that has landed at the wrong scale.

Sync and Quantize work together

The documentation describes them reinforcing each other: with BEAT SYNC and Quantize enabled, rhythm is maintained at the synchronised beat position even when triggering Hot Cues and loops. Your triggered points do not break synchronisation because both functions use the same grid.

The relationship also has a limit worth knowing:

• Setting the quantisation value to a fraction (1/16, 1/8, 1/4, 1/2) disables the tracks’ BEAT SYNC.
• Setting a fractional loop (from 1/32 to 1/2) does the same.

If Sync “drops out” when you set a short loop, that is a documented restriction. The documentation only states the disabling behaviour; the consulted sources do not explain its technical cause, so do not invent one. The useful notice for a DJ is: when synchronising, avoid fractional loops and quantisation values, or accept losing the lock.

Sync is not mixing

This is the central misunderstanding. Sync aligns beats; it does not align sections. Two tracks can be perfectly synchronised in tempo and phase yet sound wrong because one changes section halfway through the other’s section.

Everything Sync leaves unfinished remains your job:

• Choose the entry point, especially one that makes musical sense.
• Align phrases, so section changes coincide rather than cross.
• Decide when each track enters and leaves.
• Manage bass, which turns a synchronised mix into a clean one.

Sync solves the arithmetic part, which the machine does best. The musical part still depends on you, and that is what people hear.

Limits and when it gets in the way

Sync is excellent assistance and a poor crutch. Situations where it interferes or does not apply include:

• Tracks with uncorrected grids. It amplifies the error.
• Variable tempo. The lock suffers because tempo changes within the track, and the software documents specific accommodations for that case.
• Learning manual beatmatching. Depending on Sync from the outset delays ear development. Hardware or media without analysis or a grid offers no Sync to fall back on.
• No available grid or analysis. Without that information, the function has no reference.
• A synced deck preventing tempo adjustment. This is documented Traktor behaviour: correct from the master or leave synchronised mode if you need manual control.

One naming point causes considerable tutorial confusion: rekordbox has two Sync types, BEAT SYNC and BPM SYNC, selectable in preferences. Traktor also has two, BeatSync and TempoSync. “Tempo Sync” is not a rekordbox name; it belongs to Traktor. The modes’ practical differences deserve their own comparison guide.

Sync with stems

Stem separation is not a separate world: it operates on the audio playing in the deck, while Sync continues reading the analysed grid. Different layers are not necessarily independent, and documentation addresses their relationship in both directions:

• Stem functions anchor to the grid and Sync. Rekordbox warns that DRUM SWAP automatically stops when BEAT SYNC cannot be maintained—for example with a manual loop made with quantisation disabled or reverse playback—and that DRUM CAPTURE must start on the BeatGrid, requiring [Q] enabled. If Sync drops out, beatgrid-dependent stem functions drop out with it.
• Nothing documented suggests the reverse. The consulted documentation does not state that stems analysis alters a deck’s BPM or grid; the written dependency goes the other way.
• Practical risk. Muting the kick or drums with stems removes the audible reference used to check phase. If Sync slips, you will not hear it until restoring that layer. Practice heuristic: verify phase before muting drums, or keep one ear on the headphone kick while working.
• Processing cost. Serato documents stems analysis triggering by default on use, and offers preparation: Analyze Stems (on song load) analyses on loading, while the Stems crate prepares tracks before performing to avoid that cost in the booth. Prepare ahead if your computer is stretched.

Recovering from a desynchronised set

Apply this recovery procedure in order:

1. Do not keep correcting with the jog. First identify what changed: the master, a loop, a grid change or new analysis.
2. Press Sync again. Serato documentation directly instructs you to press it again to resynchronise a track that has slipped out of time.
3. If that fails, check the grid. Serato warns that an out-of-time track may have an incorrect grid or Sync disabled. Loading a track without a grid disables Sync on that deck; a BPM value alone does not make synchronisation available.
4. Find the known cause of the dropout. A fractional loop or quantisation value disables BEAT SYNC, as documented. If the dropout coincides with a short loop, that is the cause rather than a Sync failure.
5. Check whether you moved the platter. In Serato, moving the platter or playback position with Sync enabled disables Beat Sync and leaves the deck in Tempo Sync: tempo remains matched, but phase no longer does.
6. If tempo no longer matches, separate the deck, match tempo manually and lock again: tempo first, phase second.
7. Plan B: finish without Sync. Disable synchronisation and finish the mix manually. Traktor documents that a Tempo Master-synced deck does not allow manual tempo adjustment, so correct from the master or leave synchronised mode.

Common mistakes

Thinking Sync fixes an incorrectly placed grid. Sync reads the grid. If the grid lies, Sync lies with it, with perfect precision.

Using Sync before analysing and correcting. The requirement is documented: without grid information, synchronisation is impossible.

Missing which deck is master. Start playback on the other deck and master status changes. Check it before blaming Sync.

Confusing synchronisation with a good mix. They are different. Sync does not put a section change in the right place.

Setting a fractional loop and expecting Sync to hold. BEAT SYNC is documented to switch off in that situation.

Replacing manual beatmatching with Sync from day one. It is a tool, not an ear. Your reference remains knowing how to hear whether two tracks are together.