Load an audio file, choose a speed between 0.25x and 4x and pick classic or pitch-preserving mode. Press Apply, listen to the preview, then download the new WAV.
In preserve mode the tool time-stretches the waveform using overlapping grains that are cross-faded together, so the recording gets shorter or longer without the frequencies moving. Speech stays natural instead of turning into a chipmunk or a growl.
Classic mode simply resamples, exactly like changing the speed of a tape, so pitch rises when you speed up. That is what you want for sound design, for matching an old recording's pitch, or when the artefact-free result matters more than pitch.
Granular stretching is a real-time-friendly approximation, so extreme settings can introduce a slight flutter on tonal music. Between roughly 0.7x and 1.6x the result is usually transparent for speech and very close for music.