Audio Speed Changer — Free Online
Speed up or slow down any audio file without changing the pitch — entirely in your browser. 0.25× to 3× speed range. Pitch-preserving time-stretch via the SoundTouch WSOLA algorithm. No upload, no account.
How to change audio speed without changing pitch
- 1
Drop your audio files
Drag MP3, WAV, M4A, FLAC, or OGG files into the upload area — or click to select them. Files stay on your device.
- 2
Choose a speed
Click a preset (0.5×, 0.75×, 1.25×, 1.5×, 2×) or fine-tune with the slider from 0.25× to 3×. Pitch stays the same at any speed.
- 3
Select output format
MP3 for a smaller file; WAV for lossless 16-bit PCM. Use WAV if you plan to edit or re-encode the output.
- 4
Download the result
Click Change Speed. Each file shows a progress bar, then a Download button. The output name includes the speed multiplier — e.g. lecture_1_5x.mp3.
Common use cases for changing audio speed
- Speed up a 2-hour lecture recording to get through it in 80 minutes at 1.5×
- Slow down a fast-talking podcast guest to catch every word at 0.75×
- Learn a difficult guitar solo by slowing the song to 0.5× to hear each note
- Transcribe an interview more accurately by slowing to 0.75× while typing
- Speed up a language learning audio lesson to challenge your comprehension
- Slow down native-speed speech for language learners to follow pronunciation
- Fit audio narration into a fixed video duration by adjusting speed ±10%
Speed guide by use case
| Speed | Time saved on 1-hour recording | Best for |
|---|---|---|
| 0.5× | +60 min (takes 2 hrs) | Transcription, learning music passages |
| 0.75× | +15 min (takes 80 min) | Slow speakers, non-native accents, detailed study |
| 1.0× | No change | Normal playback |
| 1.25× | −12 min (takes 48 min) | Comfortable speedup, familiar content |
| 1.5× | −20 min (takes 40 min) | Most popular for lectures and podcasts |
| 1.75× | −26 min (takes 34 min) | Very familiar material, practiced listeners |
| 2.0× | −30 min (takes 30 min) | Skimming, review sessions |
How pitch-preserving time-stretch works (WSOLA)
Naive speed change (like playing a vinyl record faster) shifts pitch upward because the same number of wave cycles is delivered in less time. To change only tempo, the audio must be time-stretched — sections of the waveform are repeated or skipped while keeping the pitch-determining frequency content intact.
This tool uses the WSOLA (Waveform Similarity Overlap-Add) algorithm via the open-source SoundTouch library. WSOLA divides audio into short overlapping frames, searches for the most similar adjacent segment, and blends (cross-fades) them together — eliminating the echo artifacts of basic OLA while keeping pitch unchanged. The same algorithm powers professional DAW time-stretch plugins and YouTube's playback speed controls.
Frequently asked questions
Will speeding up audio make it sound like a chipmunk?
No — this tool uses the SoundTouch WSOLA (Waveform Similarity Overlap-Add) algorithm, which changes playback tempo independently of pitch. A 1.5× speed file sounds like the same voice speaking faster, not higher. The same principle is behind YouTube's playback speed controls.
What speed should I use for lecture recordings?
1.5× is the most popular speed for lecture playback — fast enough to save significant time while remaining fully intelligible for most speakers. 1.25× is more comfortable for dense technical content or non-native speakers. 2× is feasible for familiar material but tiring for long sessions.
What speed should I use to slow down audio for transcription or learning music?
0.75× is a comfortable slowdown that preserves naturalness. 0.5× is useful for picking out fast passages in music or dense speech. Below 0.5×, WSOLA artifacts (a "watery" echo effect) become noticeable.
Is there a difference between changing tempo and changing speed?
Speed changes both tempo (timing) and pitch together — like playing a vinyl record faster, everything shifts up. Tempo change (what this tool does) only changes timing, keeping pitch constant. "Speed change without pitch change" = tempo change.
What formats are supported?
MP3, WAV, M4A, AAC, OGG, FLAC, and OPUS — any format your browser can decode via the Web Audio API. Output is 128 kbps MP3 or 16-bit PCM WAV. Choose WAV if you plan to edit or re-encode the result further.
How long does processing take?
A 1-hour lecture at 1.5× typically takes 30–90 seconds on a modern laptop — the SoundTouch algorithm runs on your CPU in JavaScript. Longer files and extreme speeds (below 0.5× or above 2.5×) take proportionally longer. Progress is shown per file.
Is my audio uploaded to a server?
No. All processing uses the Web Audio API and SoundTouchJS running entirely in your browser tab. Your audio file never leaves your device. This is especially important for sensitive recordings like meetings, interviews, or lectures.
Can I process multiple files at once?
Yes — drop as many files as you need and click Change Speed. All files process with the same speed setting. Each file gets its own progress bar and Download button.
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