Audio Speed Changer

How to use the Audio Speed Changer

1. Choose or drag in an audio file.
2. On Change speed, pick a speed between 0.5× and 2× with the slider, the box, or a preset.
3. Tick Keep the original pitch if voices should not sound higher or lower. Leave it off for the classic tape-speed effect, where pitch follows speed.
4. Or open Change pitch to move the pitch by semitones, either keeping the length or letting the speed change with it.
5. Click Process and create WAV, listen to the result, and download it.

How it works

Speed and pitch together. The simplest way to change speed is to play the same samples faster or slower, like a record player at the wrong speed. Pitch moves with it: 2× is exactly one octave higher, 0.5× one octave lower, and 1.25× is about 3.9 semitones higher (12 × log₂ 1.25). The tool does this by handing the samples to your browser's built-in resampler (an OfflineAudioContext render), which filters the sound properly so it doesn't alias.

Keeping the pitch. To change speed without changing pitch, the tool uses a time-stretch method called WSOLA (waveform-similarity overlap-add). It cuts the sound into short overlapping windows of about 46 ms, then lays them out closer together (faster) or further apart (slower). Before placing each window it searches a small range, about ±12 ms, for the spot where the waveform lines up best with the previous window, which avoids the warbling you would get from blind cutting. It works well for speech and most music in the 0.75× to 1.5× range. Toward 0.5× or 2× you may hear some echo or roughness, especially on drums or dense mixes.

Pitch shift. A semitone change of n means a frequency factor of 2^n/12. With Keep the original length on, the tool time-stretches by that factor and then resamples back, so the length stays the same and only the pitch moves. With it off, pitch shifting is simply a speed change: +12 semitones plays at 2× speed. Example: A 440 Hz tone shifted +2 semitones becomes about 493.9 Hz.

Frequently asked questions

Why do voices sound like chipmunks when I speed up?
Without Keep the original pitch, speeding up raises the pitch along with the tempo, just like a fast-forwarded tape. Turn the option on to keep voices natural.

Is the result the same length my player would give at 1.5× speed?
Yes, the length is the original length divided by the speed. A 60-second clip at 1.5× becomes 40 seconds, and at 0.75× it becomes 80 seconds.

Why does extreme stretching sound a bit metallic?
Time-stretching has to repeat or skip tiny slices of sound. Near 0.5× or 2× the slices become noticeable, especially on percussion. Smaller changes sound much cleaner.

Which formats and sizes are supported?
MP3, WAV, M4A/AAC, OGG and FLAC (whatever your browser can play). Time-stretching a long file takes a few seconds per minute of audio. Keep files under about 30 minutes on a computer and 10 minutes on a phone.

Is my audio uploaded?
No. All processing happens in your browser, and the WAV file is created on your device.