Changing speed without changing pitch
If you simply play a recording faster, the pitch rises and voices sound like chipmunks. Play it slower and everything drops into a deep drawl. A time-stretch filter avoids this by changing the duration while keeping the pitch roughly where it was, so a voice stays natural-sounding.
This tool uses ffmpeg's atempo filter for that job. It accepts a speed between 0.5x (half speed) and 2x (double speed). A 10 minute file at 2x finishes in 5 minutes, and at 0.5x it takes 20 minutes.
Why people adjust audio speed
Speeding up is a common way to get through lectures, meetings, and spoken content in less time. Slowing down helps when you are transcribing an interview, learning a language, or working out a fast musical passage by ear.
There are limits. Very high speeds make speech hard to understand, and very low speeds can introduce a slightly warbling or smeared sound because the filter has to stretch the audio. Moderate changes, such as 1.25x or 0.8x, tend to sound the most natural. If you need to cut out a section instead of changing the speed of the whole file, use the Audio Cutter.
How to change audio speed with this tool
- Drag an audio file onto the drop area, or click it to choose one.
- Use the Speed slider that appears. It runs from 0.50x to 2.00x in steps of 0.05 and starts at 1.25x.
- Click Run. On first use the page downloads the ffmpeg engine (roughly 30MB). A progress bar shows while it works.
- Listen to the result in the audio player. To try another speed, move the slider and click Run again.
- Click Download. The output is an MP3 named after your original file with "-speed" added, for example
podcast-speed.mp3. - Start over clears the file.
Everything happens in your browser. Your audio is not uploaded.
Tips and limits
The range is fixed at 0.5x to 2x. If you need something faster or slower than that, you can run the output through the tool a second time, since each pass changes the original speed again. For example, running a file at 2x and then running that result at 2x gives you four times the original speed, though quality may suffer from repeated processing.
Always process from your original file when trying different speeds. Each run is re-encoded to MP3, so stacking changes slowly degrades the audio.
If the speed is only for listening, it can be easier to use your player's playback speed control. This tool is for when you want the sped-up or slowed-down version as an actual file. If the recording is also noisy, try the Noise Reducer on the original before changing the speed.