Audio Speed and Pitch Changer

How to change the speed or pitch of an audio file

1. Drop an audio file on the drop zone or click it to choose one (MP3, WAV, M4A, OGG, FLAC…). It is decoded in your browser.
2. Set the Speed: type a value from 0.25 to 3, drag the slider, or use a preset from 0.5× to 2×. 1 is the original speed, 0.75 is 25 % slower, 1.5 is 50 % faster.
3. Leave Keep the original pitch (change tempo only) ticked to change the tempo without the “chipmunk” or “slow-motion” effect. Untick it for a tape or turntable effect, where the pitch follows the speed.
4. Set the Pitch (semitones) to transpose, from −12 to +12. The slider moves by whole semitones; type decimals in the box for fine tuning (0.1 semitone = 10 cents).
5. Press Preview 15 s to hear the first 15 seconds with your settings.
6. Choose the Format and MP3 bitrate, then press Process and export. Listen in the player and press Download.

The New length and the total Pitch change update as you move the controls. Reset returns to 1× and 0 semitones.

Tempo, pitch and the tape effect

Playing a recording faster raises its pitch in proportion: at 2× every frequency doubles, which is one octave (12 semitones) up. In general the shift is 12 × log₂(speed) semitones, so 1.5× is about +7 semitones and 0.75× about −5.

To change the tempo alone, this tool uses SoundTouch, an open-source time-stretching library. It cuts the sound into short overlapping segments of a few tens of milliseconds and splices them back closer together (faster) or further apart (slower), choosing each splice point where the waveforms match best, so the pitch stays the same. Pitch shifting works the other way round: the tempo is stretched, then resampled back to the original length.

When Keep the original pitch (change tempo only) is unticked and the pitch is at 0, no time-stretching is needed: the tool simply resamples the audio with your browser’s own high-quality resampler, like a turntable at another speed.

Uses

• Learning music: slow a solo to 0.5× or 0.75× without changing its key, and play along.
• Transposing: move a song down 2 semitones to fit your voice, or tune a backing track to your instrument.
• Speech: speed up a lecture or a podcast to 1.25× or 1.5× while keeping voices natural.
• Effects: “nightcore” (faster and higher) or “slowed” (slower and lower) versions, with the tape mode.

Quality and limits

Time-stretching always leaves some artefacts. Between about 0.75× and 1.5×, and within a few semitones, the result is clean on most material. Extreme values (0.25× or 3×, ±12 semitones) can sound phasey or echoey, especially on drums and reverb. Processing happens on your device and takes a few seconds per minute of audio. Mono files stay mono; files with more than two channels are mixed down to stereo when SoundTouch is used.