Castos
Free Podcast Tool

Change Audio Speed Online

Speed up or slow down any audio file from 0.5x to 2x without changing the pitch. Free, private, and entirely in your browser.

Your audio stays on your device. Nothing is uploaded or stored.

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How To Change The Speed Of An Audio File

  1. Step 1

    Choose Your Audio

    Select an MP3, WAV, M4A, AAC, OGG, or FLAC file from your device. The recording stays in your browser and is never uploaded.

  2. Step 2

    Pick A Speed

    Tap a preset or drag the slider anywhere from 0.5x to 2x. The tool shows the new length right away, and you can preview the result before you commit.

  3. Step 3

    Export And Download

    Click Change Speed and download a podcast-ready MP3. The export is fixed at 128 kbps for clear spoken audio and a practical file size.

Faster Or Slower Without The Chipmunk Effect

Speed a recording up the simple way and voices climb in pitch, like a tape running fast. Slow it down and they drop into a drawl. This tool keeps the original pitch by default, so a speaker still sounds like themselves at 1.25x or 0.75x. If you want the tape-speed sound on purpose, turn off Keep the original pitch before you export.

Good Uses For A Speed Change

Speed changes work best on short, specific pieces of audio. An ad read that runs 33 seconds can fit a 30-second slot at 1.1x. An intro that was read a little too slowly can be tightened without re-recording it. Slowing a clip to 0.75x makes it easier to transcribe a fast talker or pick out a word you missed. Small adjustments are the hardest for listeners to notice, so start near 1x and move out only as far as you need.

Leave Episode Speed To Your Listeners

Most podcast apps already let listeners pick their own playback speed. If you speed up a full episode to make it shorter, anyone who already listens at 1.5x will hear it faster still. For a shorter episode, editing out tangents and dead air usually sounds better than a blanket speed change.

Podcast-Ready MP3 At 128 kbps

Every file is exported as an MP3 at 128 kbps. This is a standard podcast setting that keeps voices clear while controlling file size. There is no format menu to configure and no extra setting to second-guess.

Audio Ready? Publish Your Podcast In 3 Steps

  1. Upload a new episode in Castos

    Upload The MP3

    Create a show in Castos and upload your MP3 with your episode title, description, and artwork.

  2. Fill in podcast details in Castos

    Get Your Feed And Website

    Castos creates the RSS feed podcast apps need and a customizable site where listeners can find every episode.

  3. Link your feed to each podcast directory

    Publish Everywhere

    Submit your feed to Apple Podcasts, Spotify, and other directories once. Future episodes are distributed automatically.

Frequently Asked Questions

How do I change the speed of an audio file?
Choose an audio file above, pick a preset or drag the slider anywhere from 0.5x to 2x, and preview the result. Click Change Speed when it sounds right, then download the finished MP3.
Will changing the speed change the pitch?
Not by default. Keep the original pitch is turned on when you open the tool, so voices keep their natural tone at any speed. Turn it off if you want the tape-speed effect, where faster audio also sounds higher and slower audio sounds lower.
How long will the new file be?
Divide the original length by the speed. A 10-minute file at 1.25x becomes 8 minutes, and at 0.5x it becomes 20 minutes. The tool shows the new length before you export.
Should I speed up my whole podcast episode?
Usually not. Most podcast apps already let listeners choose their own playback speed, and someone listening at 1.5x will hear a sped-up file even faster. The tool is better suited to shorter pieces, such as fitting an ad read into a set time slot or tightening an intro that was read too slowly.
Is my audio uploaded or stored anywhere?
No. Your browser processes the audio on your device with WebAssembly. Castos never receives or stores the source file or the exported MP3. Close the tab and the working files disappear.
Which audio formats can I use?
The tool accepts MP3, WAV, M4A, AAC, OGG, and FLAC files up to 500 MB and always exports a 128 kbps MP3. Browser codec support can vary, so converting an unusual file to MP3 or WAV is the best fallback.

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Publish Your Audio With Castos

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