BPM and key
What it is
Every track you export carries two extra tags: its tempo, in beats per minute, and its musical key (E minor, F, A♭). DJ software reads them to line up mixes; GP-33 shows them in its BPM and Key columns. You don't switch anything on. We read each track after it's cut and write the numbers into the file.
How we read the tempo
We listen for the pulse. Every time the sound jumps (a drum hit, a plucked string, a strummed chord) we mark it, then we ask which steady beat lines up with the most marks. We do that across the whole track in 30-second stretches and keep the tempo that holds for the longest stretch, so a song with a slow intro or a two-part piece gets the tempo it spends most of its time in.
How we read the key
We measure how much of the track sits on each of the twelve notes, then match that shape against what a song in each key usually looks like. The closest match is the root; whether it's major or minor comes from which third sits above that root.
When we leave it blank
An honest blank beats a wrong number. We leave the tempo off when:
- the slow reading and the fast reading are a near tie.
- the track has no pulse to read: a spoken intro, a drone, silence.
- the track is shorter than ten seconds.
We leave the key off when two keys score nearly the same.
How good it is
About as good as the analyzers built into the major DJ apps, and like every one of them, not perfect. A dedicated key tool does a little better on key. Every reader, ours included, will sometimes call a slow song at double its tempo, which is why DJ apps and GP-33 carry a ÷2 / ×2 button. When a key is off, it's most often a neighbour on the Camelot wheel, which still mixes.
You can edit both numbers in GP-33's Get Info.
What we never do
We never change the audio to read it, and we never send it anywhere. The reading happens on your Mac, from the cut track, after the cut is made.
Still need help? hit us up.