Speed up or slow down audio, with or without changing the pitch

How to use the speed changer

1. Add the audio file. MP3, M4A, WAV, OGG, FLAC and WebM work, and so does the sound from an MP4 or MOV video.
2. Drag Speed (0.25× to 4× in 0.05 steps, default 1.5×).
3. Choose a Method: Keep pitch or Classic (pitch changes).
4. Pick Save as (WAV by default; M4A, WebM or OGG with a bitrate), then press Change speed.
5. Download the file. The result shows New length and Original length, and in Classic mode how many semitones the pitch moved.

What it does and when to use it

Speeding up saves time on lectures, voice messages and audiobooks you want as a file rather than relying on a player’s speed button. Slowing down helps with transcribing fast speech, learning a guitar solo, or studying a language. Classic mode is a sound-design effect: the slowed, deep “tape stop” voice or the chipmunk voice at 2×.

To change pitch while keeping the length, use the audio pitch shifter. To cut long pauses before speeding speech up, run the audio silence remover first. For video, the video speed tool changes picture and sound together.

How it works

Both methods run in a Web Worker on your device after the file is decoded.

• Classic: the audio is resampled by 1 ÷ speed with a band-limited (windowed-sinc) filter, then played at the original rate. Pitch changes by 12 × log₂(speed) semitones, so 1.5× is about +7 and 0.5× is −12.
• Keep pitch (WSOLA): the sound is cut into frames of about 46 ms with 50% overlap. For each output frame the tool searches ±10 ms around the expected input position for the piece that best matches the previous frame, then overlap-adds it with a smooth window. The search keeps waveforms in step and avoids clicks. Frame positions are chosen on a mono mix and applied to every channel, so the stereo image stays together.

Worked examples

From the tool’s output on a 60-second recording:

• 1.5×, Keep pitch: New length 0:40.00, saved as lecture-1.5x.wav.
• 0.75×, Keep pitch: New length 1:20.00.
• 0.5×, Classic: New length 2:00.00, and the summary reads “0.5× · pitch −12 semitones”, one octave down.

Limits and tips

• Speeds outside the 0.25–4× range are clamped to it.
• Slowing down makes bigger files: a slowed WAV grows in step with its new length.
• Speech above about 2× gets hard to follow even when the processing is clean. Test a short piece before converting a long file.
• The whole file is decoded into memory first, so very long recordings can fail on phones.
• Non-WAV files need your browser’s WebCodecs support (current Chrome, Edge, Firefox, or Safari 26+). MP3 output and rare inputs such as AIFF or WMA need the optional ffmpeg fallback, about 30 MB downloaded once from cdn.jsdelivr.net.