Audio Speed
Speed up or slow down audio 0.25x-4x with pitch-preserving atempo
Drag & drop files here
or browse files
Speed audio up or down with pitch-preserving atempo
About this tool
An hour-long audiobook you want to finish in forty minutes, a lecturer who speaks too slowly, a meeting recording to skim - changing speed is a daily need, yet most players turn voices into chipmunks or giants. This tool uses the FFmpeg atempo filter chain: tempo changes while pitch stays put, so 1.5x audiobooks and 2x meeting skim remain natural.
Any factor from 0.25x to 4x: 0.5x for foreign-language dictation, 2x for commutes, 3x and above for locating a passage fast. The output duration shrinks precisely by the factor, and the page shows the expected result live.
The work runs on FFmpeg compiled to WebAssembly inside your browser with nothing uploaded; output can be MP3 / WAV / M4A / OGG / FLAC, so conversion comes for free.
Features
- Any factor from 0.25x to 4x, presets 0.5 / 0.75 / 1.25 / 1.5 / 2 / 3
- atempo keeps pitch unchanged - voices stay natural
- Live output-duration estimate; speed and format in one pass
- Output as MP3 / WAV / M4A / OGG / FLAC
- Fully local processing with live progress and cancel
How to use
- Drop the audio file - duration is read
- Choose a factor (preset or custom 0.25-4)
- Pick the output format and click Apply
- Audition the result and download
Frequently asked questions
- Does the pitch change?
- No. The atempo filter stretches time without shifting pitch, which is why 2x audiobooks still sound human. At the extremes (0.25x or 4x) the algorithm leaves slight artifacts - normal for any time-stretcher.
- Why is 4x the limit?
- A single atempo stage covers only 0.5-2.0; the tool cascades stages to reach 0.25-4. Beyond that the result stops making sense to listen to. To find something in a long recording, cut the relevant segment first with the Audio Cutter.
- Does speed change hurt quality?
- Speed change requires re-encoding - there is no lossless tempo change. One high-quality encode is inaudible; keeping the bitrate at or above the source level minimises the loss.