Audio Speed Changer
Faster podcasts, slower practice, nightcore or slowed + reverb — in pitch or not.
Try before you buy.
- Free preview: the first half of the result (up to 30 seconds) at the speed and format you chose, with a short MySmartCoPilot chime every 10 seconds.
- Locked until you unlock it: download.
- Unlock: Pro pass, ₹179 for 30 days, a one-time payment that never renews.
Ways to unlock shows how to get the full result.
Printing this result is locked in the free preview.
Play starts at A. Drag A and B on the waveform to choose the part to hear (or loop, to practise).
Your new file
Locked in the free preview. Opens the ways to unlock this result.
Locked in the free preview. Batch runs unlock with a pass.
Locked in the free preview. Query results unlock with a pass.
About the Audio Speed Changer
Change how fast a recording plays — anywhere from 0.25× to 4× — and, with a pass, save the result as MP3, M4A or WAV. Keep the pitch to listen to podcasts and lectures faster or to slow a song down for practice without it sounding lower; the time-stretching is done with Signalsmith Stretch, a high-quality open-source stretcher. Or change the speed like a tape, where the pitch rises and falls with it — the sound of nightcore (faster and higher) and slowed + reverb (slower and lower, with a room added).
The waveform has an A–B selection: press Play to hear the speed live from A, loop A–B to practise a passage, change the speed while it plays, and export just that part if you like. Long lectures and audiobooks are processed in one-minute pieces, so even hours of audio do not run out of memory.
Everything runs in your browser; the file is never uploaded. Without a pass, the result is a free preview: its first half (up to 30 seconds) with a short MySmartCoPilot chime every 10 seconds, and the live player plays with the chime too.
How to use it
- Drop an audio file on the box, or press Choose an audio file. Its waveform appears.
- Pick a preset — 1.25×, 1.5×, 2×, 0.75×, 0.5×, Nightcore or Slowed + reverb — or set any speed with the slider or by typing it (for example 1.35 or 135%).
- Choose Keep the pitch or Like a tape (the pitch moves with the speed), and add reverb if you want. Press Play to listen from A; tick Loop A–B to repeat a part.
- Choose MP3, M4A or WAV (and Only the A–B part if you want just that), press Change the speed, then Download, with a pass or after unlocking this result. Without a pass the page plays a free preview instead: the first half (up to 30 seconds) with a short MySmartCoPilot chime every 10 seconds.
Examples
lecture.mp3 · 1:30:00 · keep the pitch
lecture (1.5x).mp3 · 1:00:00 · same voices, a third less time
song.m4a · A 2:05.0 → B 2:21.5 · 0.75× · keep the pitch · loop A–B
Practise along with the loop at 0.75×, then save only the A–B part (22 seconds) as WAV
track.mp3 · 3:12 · preset Slowed + reverb (0.8×, like a tape, reverb 35%)
track (0.8x).mp3 · 4:03 · 3.9 semitones lower, with a reverb tail at the end
Keep the pitch or change it like a tape?
Keep the pitch (time-stretching) re-synthesises the sound so it lasts longer or shorter at the same pitch: voices still sound like themselves at 1.5×, and a song slowed to 0.75× stays in its key. Quality is best between about 0.5× and 2×; at the extremes, speech starts to sound phasey or choppy.
Like a tape plays the samples faster or slower, as a record or tape would: the pitch moves by 12 × log₂(speed) semitones — 1.25× is 3.9 semitones higher, 0.8× is 3.9 semitones lower, 2× an octave higher. It sounds completely natural (nothing is re-synthesised), which is why nightcore and slowed edits use it.
How long the result will be
A speed of s makes the audio last 1 ÷ s as long: 60 minutes at 1.25× take 48 minutes, at 1.5× 40 minutes, at 2× 30 minutes; at 0.75× a 3-minute song takes 4 minutes. With reverb, about 3 seconds of the room ringing on are added at the end.
How it works
Keeping the pitch uses Signalsmith Stretch (MIT licence), which runs as WebAssembly in your browser’s audio engine. The download is rendered in one-minute pieces with a second of extra audio on each side, joined with 100 ms crossfades, so memory use stays small. The tape mode uses a band-limited resampler, so speeding up does not add aliasing. The reverb is a Freeverb design (eight comb and four all-pass filters per side, public domain); the preview plays its exact impulse response, so what you hear is what you get.
Limitations
- Keep-pitch quality drops at very low and very high speeds (below about 0.5× and above 2×), especially for speech.
- The live preview holds up to two minutes from A in memory; the download, with a pass or after unlocking it, always covers the whole file (or the A–B part).
- Changing the pitch without changing the speed is not offered here.
- One file at a time. Video files give their sound only; to change a video’s speed with its picture, use the Video Speed Changer.
Privacy
Everything happens in your browser. What you enter or open here is not uploaded or stored by MySmartCoPilot. The audio engine, the time-stretcher and the encoders download from MySmartCoPilot the first time you use them. Your audio is never uploaded.
Frequently asked questions
What do I get without a pass?
Without a pass, Audio Speed Changer shows the first half of the result (up to 30 seconds) at the speed and format you chose, with a short MySmartCoPilot chime every 10 seconds. Until you unlock it, the result can’t be downloaded. A Pro, Premium or Ultimate pass, a one-time payment that never renews, unlocks the full result. The pricing page lists the passes and their prices.
How do I speed up audio without making voices sound like chipmunks?
Choose Keep the pitch (the default). The speed changes and the pitch stays where it was, so 1.25× to 2× still sound natural.
How do I make a “slowed + reverb” or “nightcore” version?
Press the Slowed + reverb preset (0.8×, like a tape, with reverb) or Nightcore (1.25×, like a tape), adjust the speed and reverb to taste, listen, and press Change the speed.
Can I loop a part to practise it?
Yes. Drag A and B on the waveform around the part, tick Loop A–B, press Play, and change the speed while it plays until you can keep up.
Can I change a whole audiobook or lecture?
Yes. Long files are processed a minute at a time, so a several-hour file works; it takes a while (the progress bar shows how far it is) and the result is kept in the browser until you download it, with a pass or after unlocking it.
Which format should I save as?
MP3 for players and phones, M4A for Apple devices, WAV to keep editing it in an audio editor or DAW without another lossy step.
Is my file uploaded?
No. Decoding, stretching and encoding all happen in your browser.