AnyTool
Your files never leave your device. All processing happens locally in your browser.

How do I slow down or speed up audio without changing the pitch online?

Open AnyTool's Audio Time Stretch, drop in your file, and drag the speed slider (0.25x–4x) — or type an exact target duration or target BPM — and the tempo changes while the pitch stays the same, with a true real-time preview you can hear while playing. Loop a region, add an independent pitch shift, or use an extreme PaulStretch-style mode for ambient stretching, then export WAV, MP3, M4A, OGG or FLAC. Everything runs in your browser with a WSOLA engine and a self-hosted ffmpeg encoder — no upload, no watermark, no length cap, no CDN.

  • Change tempo/duration without changing pitch (0.25x–4x)
  • Speed, exact target-duration and target-BPM modes with live WSOLA preview
  • Independent pitch shift, region loop and an extreme ambient-stretch mode
  • 100% in your browser — no upload, no watermark, no length cap, no CDN

What is

Time stretching

Time stretching changes the tempo or duration of audio without altering its pitch — the opposite of resampling, which changes both together. It can be driven by a speed factor, an exact target length, or a target BPM detected from the source. A client-side time-stretch tool previews this in real time in the browser with a WSOLA engine and exports via ffmpeg, with nothing uploaded.

Audio Tools

Related terms

tempoBPMWSOLApreserve pitchPaulStretch

How to Time-Stretch Audio

Change audio tempo without changing pitch in your browser.

20 secWeb browser
  1. 1

    Add audio

    Drop in any audio file — it stays on your device.

  2. 2

    Set the tempo

    Drag the speed slider or enter a target duration/BPM and hear the result live.

  3. 3

    Export

    Download as WAV, MP3, M4A, OGG or FLAC — nothing is uploaded.

Result: A time-stretched audio file

Frequently Asked Questions

No — the tempo changes while the pitch stays the same.

A WSOLA time-stretch engine preserves pitch in both the preview and the exported file, fixing the classic "tape" effect where speed and pitch change together.

Yes — type a target length (mm:ss) or a target BPM and it solves the factor.

Target-duration mode reverse-solves the tempo from your length, and target-BPM detects the source BPM and stretches to your chosen tempo — both beyond most free tools.

No — stretching runs entirely in your browser.

The file never leaves your device with no length or size cap, unlike AudioAlter (50 MB), Audiotrimmer (100 MB) or VEED/Clideo (watermark + upload).

Detailed Explanation

Methodology

How the Audio Time Stretch Works

AnyTool changes tempo without changing pitch entirely in the browser. For preview it uses a WSOLA time-stretch engine in an AudioWorklet, so dragging the speed slider (0.25x–4x) or setting a target duration/BPM is heard live and pitch-preserving, with a waveform, region select and loop. Three modes drive the factor: Speed (direct), Target-duration (factor = source ÷ target), and Target-BPM (the source BPM is detected from the decoded buffer, then factor = target ÷ source). For export the shared self-hosted single-threaded ffmpeg.wasm engine (bundled core, no CDN) applies a pitch-preserving atempo chain (auto-chained to stay within the per-stage window across 0.25x–4x) and encodes WAV, MP3 (libmp3lame), M4A (AAC), OGG (libvorbis) or FLAC; an extreme spectral-smoothing mode handles ambient stretches beyond 4x.

  • Runs client-side — the audio is never uploaded
  • WSOLA preview changes tempo without changing pitch
  • Speed, target-duration and target-BPM modes
  • Region loop and an extreme ambient-stretch mode
  • Self-hosted ffmpeg core (bundled) — no CDN
  • Export WAV/MP3/M4A/OGG/FLAC
Privacy & Security

Privacy vs Cloud Speed Changers

123apps and AudioAlter upload to a server, Audiotrimmer caps files at 100 MB, VocalRemover.org limits input to 10 minutes, and VEED/Clideo watermark and paywall their output. AnyTool stretches on the device, so the file never leaves the browser, with no size or length cap, watermark or sign-up. Crucially, both the preview and the exported file are genuinely pitch-preserving — fixing the common bug where speed and pitch change together — and it adds target-duration, target-BPM and a real-time WSOLA preview that server tools cannot match.

Time stretching: AnyTool vs typical tools
CapabilityAnyToolTypical tools
Data handlingIn your browserOften uploaded
Pitch preservedYes (preview + export)Sometimes
Target duration / BPMYesRare
Real-time previewYes (WSOLA)Often re-render
Watermark / capNoneCommon

AnyTool is a privacy-first client-side time stretcher — stretching runs locally and nothing is uploaded.