Audio Speed Changer
Time-stretch audio between 0.5× (half speed) and 2× (double speed) while keeping the original pitch intact.
The same kind of processing your DAW does when you warp a sample or your DJ software does when it sync-locks two tracks at different tempos. Useful for transcribing solos, slowing down lyrics, speeding up podcasts, or matching tempos.
How it works.
- 1Drop the audioMusic, voice, anything. Decoded locally.
- 2Pick a speed0.5× . Half speed, useful for transcribing fast passages. 0.75× . Slow practice tempo. 1.25-1.5× . Most podcast listeners' preferred speed-up. 2× . Double speed for skim listening.
- 3Processffmpeg's atempo filter rearranges short audio frames (~20 ms each). Repeating or skipping them. To change duration without changing pitch. Quality is transparent within 0.5-2× for music; outside that range artifacts become noticeable.
Slow down a song without turning the singer into a monster
Speed a record up the old-fashioned way and everything goes chipmunk; slow it down and the vocalist drops an octave. This tool time-stretches instead, it changes how long the audio plays while the pitch stays exactly where it was. Slow a guitar solo to half speed to learn it note by note, or push a podcast to 1.5× and it still sounds like the same person talking, just faster.
- 0.5× half speedTranscribe fast solos and lyrics
- 0.75×Comfortable practice tempo
- 1.25 to 1.5×Podcast and lecture speed-listening
- 2× double speedSkim through long recordings
No upload, no queue, no watermark
The audio is processed on your own machine with ffmpeg compiled to WebAssembly, the identical time-stretch a desktop editor would run. Your file never touches a server, and a 200 MB recording processes about as fast as your laptop can read it.
Made for practice, transcription, and DJ prep
Changing audio speed is a musician's problem more often than a file-format one: learning a fast passage, slowing lyrics down to write them out, matching a track's tempo before a mix. That's why the range is capped at 0.5 to 2×, the zone where time-stretching stays clean, instead of letting you dial in 10× and handing back audio that sounds like it's underwater.
How to change the speed of a song
Step by step
- Drop an MP3, WAV, FLAC, OGG, M4A, AAC or AIFF file into the tool above (up to 200 MB).
- Click a preset (0.5×, 0.75×, 1.25×, 1.5×, 1.75×, 2×) or move the slider in 0.05 steps.
- Press Change speed. The file is processed on your device.
- Play the result in the page, then download the WAV.
Speed and BPM
New BPM = original BPM × speed. For a 120 BPM song:
| Speed | New tempo | Good for |
|---|---|---|
| 0.5× | 60 BPM | Learn a fast solo note by note |
| 0.75× | 90 BPM | Practice at a comfortable tempo |
| 0.85× | 102 BPM | Base for a slowed version |
| 1.25× | 150 BPM | Sped-up version, podcasts |
| 1.5× | 180 BPM | Lectures and voice notes |
| 2× | 240 BPM | Skim a long recording |
Do not know the tempo? Find it first with the Key & BPM Finder.
Making slowed and sped-up versions
This tool keeps the pitch. The popular “slowed” and “sped up” edits change the pitch too, the way a record does when it plays slower or faster. To get that sound, use two tools:
- Slowed: set 0.85× here, then lower the result by 3 semitones in the Pitch Shifter. A record played at 0.85× drops about 2.8 semitones.
- Sped up / nightcore: set 1.25× here, then raise it by 4 semitones. A record played at 1.25× rises about 3.9 semitones.
Mistakes to avoid
- Expecting perfect drums at 0.5× or 2×. Sharp hits can sound slightly smeared or doubled at the ends of the range. Between 0.75× and 1.5× most music sounds clean.
- Processing a whole album track to practise one solo. Cut the part first with the Audio Trimmer; it is faster and the file is smaller.
- Uploading a low-quality MP3 for a release. Speed changes make encoding artefacts easier to hear, so start from the WAV if you have it.
Questions.
Why doesn't the pitch change when speed changes?
If you sped up audio the way a record player does (raising playback rate), pitch goes up too. Time-stretching uses overlap-add windowing instead. It splits audio into short frames and either repeats them (slowing down) or drops some (speeding up). The frame-level pitch content is preserved, only the timeline changes.
Does the audio degrade at extreme speeds?
At 0.5× and 2× the artifacts are subtle. Slight echo or warble on transient sounds (drums, percussion, plucked strings). Below 0.5× or above 2× artifacts become obvious. This tool caps at 0.5-2× for that reason. For more extreme stretching, dedicated tools like RubberBand do better.
Speed change vs pitch change. What's the difference?
Speed changer changes how long the audio plays, keeping pitch the same. Pitch shifter changes the pitch (key) without changing how long the audio plays. Use speed for transcription/practice/playback rate; use pitch shift to transpose a song into a different key.
How do I slow down a song without changing the pitch?
Upload the song, set the speed below 1×, for example 0.75×, and press Change speed. The tool time-stretches the audio, so the song gets longer but stays in the same key.
How do I change a song to a specific BPM?
Divide the BPM you want by the song's BPM. For a 124 BPM song you want at 130, that is 130 ÷ 124 = 1.05, so set 1.05×. The slider moves in 0.05 steps, so you can get within about 2.5% of any target.
What file do I get?
A 16-bit WAV at the original sample rate, named with the speed, for example song_0.75x.wav. A WAV is about 10 MB per minute of stereo audio at 44.1 kHz.
Why not chain multiple atempo filters for extreme speeds?
ffmpeg's atempo only accepts 0.5-2.0 in a single application. For wider ranges you can chain (e.g., atempo=2.0,atempo=2.0 for 4×), but artifacts compound. The 0.5-2× single-stage range is where time-stretching stays transparent for most material.