Change the key of a song without changing its speed, or slow a recording down without lowering it - to sing along in your own range, learn a fast solo, transcribe a lecture or match a track to another. The pitch and speed are changed by Signalsmith Stretch, a high-quality time-stretching library, with an option that keeps voices sounding like themselves when the pitch moves. You hear each change as you make it, and can loop the bar you are practising. It is free to use, with no account and no upload limit, and it runs entirely in your browser: nothing is uploaded, and while the page stays open, a feature you have already used keeps working offline.
- Does changing the pitch change the speed?
- No. Pitch and tempo are separate here: a song moved up two semitones keeps its length, and one slowed to 75% keeps its key. Changing both at once works too.
- What does formant preservation do?
- A voice has a pitch, the notes sung, and formants, the resonances of the throat and mouth that make it sound like that person. Plain pitch shifting moves both, which is why a raised voice sounds like a cartoon. With Keep voices natural on, the notes move and the formants stay, so the singer still sounds like themselves a few semitones up or down.
- How many semitones is a key change?
- One semitone is one step on a piano, black keys included, so moving from C to D is +2 and from G down to E is −3. Set the original key under Musical help and the page shows the key you end up in.
- Can I slow down a song to learn it?
- Yes. Set the tempo to 50-75%, mark the passage with Set A and Set B, and press Loop: it repeats at that speed, in the original key, until you stop it. Raise the tempo step by step as you get it.
- Can it fix a recording that is slightly out of tune?
- For the whole recording, yes: type a fraction of a semitone, such as 0.3 or −0.15, to move everything up or down by that much. It cannot correct individual notes, as pitch-correction software does.
- Is my music uploaded?
- No. The file is read and processed in your browser, and the saved file is made there too. MP3, M4A and FLAC are written by an encoder that runs on this page.