How the pitch shift works here
With Keep the Tempo on, the shift runs through Signalsmith Stretch, a phase-vocoder pitch and time engine compiled to WebAssembly. It analyses the audio in short overlapping frames, moves every frequency up or down by the interval you pick and resynthesises the result at the original length, so the song keeps its exact duration and beat.
With Keep the Tempo switched off, nothing is stretched: the audio is simply resampled, the full turntable effect, with pitch and length moving together. That mode is a genuinely different sound, not just a shortcut, and it stays perfectly clean at any shift. Either way, press Play preview and drag the slider to hear the new key before you export.