Pitching a sample

From pitch to tempo

With repitch, shifting by +2 semitones multiplies the playback speed by 1.1225. A loop at 90 BPM therefore moves to 101.02 BPM, and its 4 bars last 9.5 seconds instead of 10.67.

From tempo to pitch

Going from 90 to 95 BPM with repitch raises the sample by 0.94 semitones. That is not a whole number of semitones: the sample will sound out of tune with the rest. Stick with time-stretch, or choose 95.35 BPM, which gives exactly +1 semitone.

Repitch, time-stretch and formants

With repitch, your DAW plays the sample faster or slower, like speeding up a record: pitch and tempo change together. Going up one half step multiplies the speed by about 1.0595, and going up an octave, which is 12 half steps, doubles it exactly.

Time-stretch, on the other hand, changes the length without touching the pitch, and its opposite, pitch-shifting, changes the pitch without touching the length. Both slice the sound into tiny pieces. Pushed too far, it leaves artifacts: soft transients, a metallic or grainy sound.

Formants are the resonances that give a voice or an instrument its character. With repitch, they move with the note: a voice pitched up sounds like a cartoon character, a voice pitched down sounds huge. Formant-preserving algorithms change the note while keeping that character.