Change a track's tempo and see the speed ratio, the pitch shift in semitones if you vari-speed it, and the new duration.
Speed ratio = target ÷ original BPM. Played vari-speed (like vinyl or a repitched sampler), pitch moves with speed: semitones = 12 × log2(ratio), so 100 → 120 BPM raises pitch 3.16 semitones. Time-stretch algorithms keep pitch constant instead, at the cost of artefacts on large stretches.
If the audio is simply played faster (vari-speed), pitch rises with it: 12 × log2 of the speed ratio in semitones. Going 100 to 120 BPM is a 1.2x ratio, about +3.16 semitones.
Vari-speed changes tempo and pitch together, like speeding up vinyl — clean but transposed. Time-stretch algorithms change tempo while holding pitch, which preserves the key but can smear transients on big changes.
Within about ±10% most algorithms sound transparent; beyond ±20% artefacts get audible on complex material. For big jumps, consider vari-speed plus a separate pitch correction, or choose a track closer in tempo.