BrowserTools

Audio Speed Changer

Speed up or slow down audio, pitch-safe

By Guga — BrowserTools maintainer, Tbilisi, Georgia Updated 2026-08-19
Free Private No uploads

A one-time ~30 MB pull of the WebAssembly FFmpeg core from unpkg.com powers the retiming; your browser caches it afterwards. The atempo filter runs in the tab and your file stays local.

What is Audio Speed Changer?

The tempo moves; the pitch does not. FFmpeg's atempo filter time-stretches the waveform rather than resampling it, so a voice at double speed is recognisably the same voice and not a chipmunk. Range is 0.5x to 2x in steps of 0.05, with chips for the common values. Duration scales exactly inversely: at 1.5x a 20-minute recording comes out around 13 minutes 20 seconds, and at 0.75x an 8-minute lecture stretches to roughly 10 minutes 40 seconds. The trade is a small amount of transient smearing on sharp percussive material, which is inherent to time-domain stretching rather than a fault here. Output is always MP3 at variable bitrate, so a WAV input gains a lossy step on the way out.

Change the tempo of any audio file from 0.5x to 2x while keeping the pitch natural. Great for practicing music, speeding up lectures and creating effects.

Private Audio Speed Changer In Your Browser

Audio Speed Changer is processed locally with client-side JavaScript. Your files never touch a server, and there is no queue to wait in.

Step-by-Step

How to use Audio Speed Changer

1

Choose the file to retime; anything from an MP3 to a FLAC master, or the audio half of a video, will do.

2

Move the Speed slider between 0.5x and 2x, or tap one of the 0.75x, 1.25x, 1.5x, 1.75x or 2x presets.

3

Press Apply speed change. The filter runs faster than real time, once the one-off media engine has arrived.

4

Play the retimed result in the audio player, then download the MP3.

Key Capabilities
  • Adjusts tempo continuously from 0.5x to 2x in 0.05 steps, with five one-click presets.
  • Preserves pitch by time-stretching the waveform rather than resampling it.
  • Produces a new file whose duration changes inversely with the chosen speed.
  • Writes MP3 at variable bitrate quality level 2, playable in any common player.
Common Use Cases
  • A language student slowing a native-speed interview to 0.75x so the grammar is audible.
  • A commuter cutting a 45-minute podcast down to 30 minutes at 1.5x for the drive home.
  • A musician preparing a slowed reference track to transcribe a guitar part note by note.
Clear Answers

Frequently Asked Questions

Does it really keep the pitch, or just sound chipmunky?
Genuinely keeps it. atempo overlaps and cross-correlates windows of the waveform to stretch time, so a pitched note stays at the same frequency. Speed it up and a baritone voice still sounds like a baritone — just faster and, inevitably, more breathless.
Why can I not go beyond 2x or below 0.5x?
The slider is bounded there, and the filter is applied in a single pass. Values outside that range need the filter to be chained, which this page does not do — so a request for 0.25x or 4x is simply not offered rather than approximated.
How do I work out the resulting length?
Divide. Original duration in seconds, over the multiplier: a 3,600-second hour at 1.25x becomes 2,880 seconds, and at 0.8x it becomes 4,500. The output player shows the real length once it is encoded.
Is a very fast or very slow result going to sound clean?
At the extremes, less so. Time-domain stretching has to reuse and blend audio to fill the gap, and the artefacts compound the further you move from 1x. Expect soft drum attacks and slight doubling on sibilants at 1.75x and above, and a slightly smeared, dragging quality below 0.7x.