Understanding BPM and Beatgrids

DJ software shows you a BPM value and a grid of lines over the waveform. Both look simple – but most problems with loops, sync and edits come from a grid that doesn’t sit exactly on the music.

BPM: the tempo

BPM (beats per minute) is the tempo of a track. At 120 BPM, one beat lasts exactly 0.5 seconds; at 128 BPM, 0.469 seconds.

BPM alone doesn’t tell the software where the beats are. Two tracks can both be 128 BPM but start their first beat at completely different moments.

Beatgrid: tempo + position

A beatgrid is a set of markers – one per beat, with the first beat of every bar (the downbeat) highlighted. For a track with steady tempo it’s defined by just two numbers:

1. the tempo (BPM) – the distance between the lines, and
2. the offset – where the first downbeat sits in the file.

If either is off, the grid drifts away from the music.

Typical grid problems

• Wrong offset: the BPM is correct, but all lines sit slightly before or after the kicks. Loops then start with a tiny gap or cut off the attack.
• Half or double tempo: a 140 BPM track detected as 70 BPM (or vice versa). Bar lengths are then wrong by a factor of two.
• Downbeat on the wrong beat: the grid is on the beats, but “beat 1” is actually beat 3. Bars and phrases are shifted by half a bar.
• Slight tempo error: e.g. 127.9 instead of 128 BPM. At the start everything looks fine, but after a few minutes the grid is visibly off.
• Variable tempo: live-played music doesn’t keep a perfectly constant tempo, so one fixed grid can’t fit everywhere.

How to check a grid

1. Zoom in on a few kicks at the start, in the middle and at the end of the track. The grid lines should sit on the start of each kick, everywhere.
2. Listen with a metronome or click on top of the track. Any drift becomes obvious within a few bars.
3. Check the downbeat: does the drop or the vocal entry start on a bar line (beat 1)?

Why it matters for edits

An intro edit loops bars and then hands over to the original track. If the grid is off by even a few milliseconds, every loop seam and the transition into the track are off by the same amount – and you hear it.

Beatgrids in DJsExtended

DJsExtended detects tempo and grid on its own when a track loads, and can also use the grid from your Serato library. You can correct the grid (tempo and offset separately), check it with a metronome and always restore the original grid.