Slowed + Reverb Maker

Yes. It is completely free, with no sign-up, no watermark and no limit on how many songs you process.

No. The file is decoded and processed entirely in your browser with the Web Audio API. Your audio never leaves your device, which also means the tool works offline once the page has loaded.

It is a remix style that slows a track down and adds a wide reverb tail, which makes it sound dreamier and more spacious. Slowing a song also lowers its pitch, and that drop is part of the sound.

Yes. The speed slider moves tempo and pitch together for the classic slowed sound, and the separate pitch slider shifts pitch in semitones while leaving the tempo where it is.

Anything your browser can decode, which normally covers MP3, WAV, M4A, AAC, OGG and FLAC. Files up to 60 MB are accepted.

A 16-bit WAV, so the audio does not go through a second round of lossy compression. WAV files are large, so a long track can run to a few hundred megabytes.

Pick the Nightcore preset, or set the speed above 1.00x and add a couple of semitones of pitch. Nightcore is the same idea as slowed and reverb, just in the opposite direction.

The tool adds no restriction of its own, but the song still belongs to its rights holder. Make sure you have the right to publish the track you upload.