Audio Speed Changer

How to change audio speed without changing pitch

Slowing a tape machine down shifts both tempo and pitch together — vocals become deep and sluggish. Modern time-stretching separates the two: a phase vocoder analyzes the sound in overlapping frequency frames and re-synthesizes them closer together or further apart, keeping every frequency where it was while shortening or lengthening the timeline. That is what the 'Preserve pitch' option does here.

If you want the classic vinyl/tape effect, just switch pitch preservation off: 0.9× gives you the pitch-drop of slowing a record.

Common uses for an audio speed changer

• Practice: slow difficult solos to 0.75× to learn them note-for-note.
• Transcription: transcribe fast passages accurately at reduced speed.
• DJ prep: pre-adjust tracks so beatmatching needs less pitch riding.
• Content: speed up podcasts or voice notes to 1.5× for review.
• Fitness: nudge songs up a few percent to match a running cadence.

BPM changer: changing a song's tempo by number

Whether you call it a speed changer or a BPM changer, it's the same operation: the percentage you move the speed slider is exactly the percentage the BPM moves. Slowing a track from 126 to 122 BPM is a 3% speed change — set the slider to 0.97× and you're there. DJs use this constantly to nudge a song into a target BPM window for beatmatching; fitness runners do the same to lock a playlist to their cadence. If you don't know the track's current BPM, run it through the BPM Finder first, then come back and dial in the exact tempo you need.

Quality notes

The live preview uses your browser's built-in high-quality time-stretch, and the exported WAV is rendered with a phase-vocoder using identity phase locking — the same family of algorithms used by DAW time-stretch presets. Modest changes (0.7×–1.4×) sound essentially transparent; extreme stretch factors introduce progressively more processing artifacts, especially on sparse transients.