What Is an Audio Speed Changer?
An audio speed changer increases or decreases the tempo of a recording, making it play faster or slower with a correspondingly shorter or longer duration. Preserve Pitch mode changes tempo without intentionally moving voices or notes higher or lower. Natural Speed Change links the two properties, like playing tape or vinyl at a different rate.
Common uses include speeding up podcasts and lectures, slowing speech for transcription or language practice, rehearsing music at a more manageable tempo, creating tape-style effects, and transposing a recording by semitones. This tool previews the settings locally and creates MP3, WAV, OGG, or M4A output in your browser.
How to Change Audio Speed or Pitch
- 1
Upload audio
Choose a supported audio file or a video file that contains an audio track.
- 2
Set the speed
Use a preset, slider, or the precise number control to choose 0.25×–4×.
- 3
Choose a pitch mode
Preserve pitch, change speed and pitch naturally, or shift pitch only by semitones.
- 4
Preview the result
Listen with the live preview and confirm the estimated output duration.
- 5
Process and verify
Select MP3, WAV, OGG, or M4A, process locally, then preview the exact export.
Speed vs. Pitch — What's the Difference?
Pitch-Preserved Speed Change
Time-stretchThe tempo changes while the musical pitch is intended to remain stable. A speaker at 1.5× talks faster without the automatic octave rise caused by simple resampling. This tool exports the effect with FFmpeg's atempo filter. Very large changes can still introduce audible artifacts.
Natural Speed Change
ResampleSpeed and pitch change together, exactly like playing a tape or record faster. Doubling the speed raises the pitch by one octave. This can create nightcore-style speed-ups, lowered slowed-down audio for later effects work, chipmunk voices, and tape-style sound design. Export uses FFmpeg's asetrate filter.
Pitch Shifting in Semitones
A semitone is the smallest interval in Western music — the distance between adjacent keys on a piano. There are 12 semitones in an octave. Shifting pitch by +12 semitones raises it exactly one octave; −12 semitones lowers it one octave. Common musical uses: shifting a song from the key of C to D is +2 semitones. Transposing from E to A is +5 semitones. The tool supports ±12 semitones (a full octave in either direction) with 1-semitone precision.
| Semitones | Effect | Music Use |
|---|---|---|
| +12 | One octave higher | Harmonize above, create ultra-bright vocal effect |
| +5 | Perfect fourth up | Transpose C → F, G → C |
| +2 | Whole tone up | Transpose C → D, common key change |
| +1 | Semitone up | C → C♯/D♭ |
| 0 | No change | Original pitch |
| −1 | Semitone down | C → B |
| −2 | Whole tone down | Transpose D → C |
| −5 | Perfect fourth down | Transpose F → C |
| −12 | One octave lower | Deep bass effect, lo-fi or horror audio |
Common Speed Settings & Use Cases
Slow-motion effect, transcription, music practice
Calm listening, 'slowed + reverb' aesthetic (with natural mode)
Original speed — no change
Light speed-up for lectures and dense content
The most popular podcast speed — saves 33% of listening time
Fast content consumption for familiar topics
Double speed — half the time, high comprehension for practiced listeners
Extreme review mode, scanning recordings, audio skimming
Frequently Asked Questions
Technical note: Pitch-preserved speed change uses FFmpeg's atempo filter. The tool chains stages below 0.5× and above 2×; FFmpeg notes that a single stage above 2× may skip samples instead of blending them. Natural speed change uses asetrate to reinterpret samples at a different rate, changing speed and pitch together. Pitch-only shift combines asetrate with a compensating atempo to shift pitch while keeping tempo. All processing runs via FFmpeg compiled to WebAssembly, entirely in your browser.