The tool resamples your audio at a different rate. Faster = higher pitch (like fast-forwarding a tape). Slower = lower pitch. This is the simple/direct approach. For pitch-preserved speed change you need WSOLA or phase vocoder algorithms, which the Loudify app handles natively.
Common use cases
1.5× / 2× — speed-listen to podcasts and lectures
0.5× / 0.75× — slow down music for transcription or instrument practice