- Why slow down music without changing pitch?
- The most common use is instrument practice — slowing a fast guitar solo or piano run to 60% makes every note audible and playable, then you raise the tempo gradually until you match the original. Singers use it to memorize melody at a comfortable speed without the notes sounding lower. Language learners slow down native speakers to catch every word. DJs and beatmakers transpose backing tracks to match a vocalist's range. Standard playback-rate controls lower pitch in proportion to speed (the "chipmunk" or "slow-mo" effect), making them useless for these tasks — pitch-preserving time-stretching decouples the two.
- What is A-B loop and how do I use it?
- A-B repeat (also called "interval loop") lets you isolate a short passage — say, bars 5 through 8 — so it plays continuously without you having to rewind manually. Seek to the moment you want the loop to start, then click "Set A." Seek to where you want it to end, then click "Set B." Playback wraps back to A every time it reaches B. Click "Clear" to remove the loop markers and resume normal playback. You can set new A or B points at any time while playing.
- How much can I slow down or speed up?
- The tempo slider runs from 25% (quarter speed) to 200% (double speed). Below about 40%, gentle time-stretch artifacts become audible because the algorithm must repeat audio windows to fill in the stretched time — the effect is similar to a very slight "phasing" or "fluttering." Most practice use cases stay between 50% and 80%, where the result sounds completely natural. Above 150% the audio stays clear and intelligible, which is useful for listening to lectures or podcasts at higher speeds while keeping the original pitch.
- What does the key / semitone shift do?
- It raises or lowers the musical pitch of the entire track in equal-tempered semitone steps, independently of tempo. Twelve semitones equals one octave. A shift of +5 moves the key of C to F. Common uses: transposing a backing track to suit a singer's vocal range; adjusting an old recording that was not tuned to standard A-440; or checking how a chord progression sounds in a different key before transposing your own part. You can combine tempo and pitch changes freely — for example, slow to 70% and shift down 2 semitones simultaneously.
- Which audio formats are supported?
- Any format your browser can decode natively — in practice that means MP3, WAV, AAC/M4A, OGG Vorbis, FLAC, Opus, and WebM audio on most modern browsers. The file is decoded by the browser's built-in codec (the same engine used for <audio> tags), so there is no additional conversion step and the full bit-depth quality of the original file is used throughout processing.
- Is my audio uploaded to a server?
- No. The file is read from your disk using the browser's File API, decoded in memory, and processed entirely on your own CPU using the Web Audio API. No audio data — and no metadata such as your filename — is transmitted anywhere. The tool does not require an account, and once the page has loaded it will work even without an internet connection. This makes it safe to use with copyrighted material, personal recordings, or anything privacy-sensitive.