Speed up or slow down audio playback from 0.25x to 4x without changing pitch. Perfect for transcription, music practice, podcast speed adjustment, and audiobook listening.
Speed up or slow down audio playback without changing pitch, or change both speed and pitch together. Drag the speed slider from 0.25x to 4x and hear the result immediately. Great for transcription work, language study, music practice, or fitting audio into a specific time window.
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Generate beautiful waveform visualizations from audio files. Choose from bars, mirror, line, or circular styles. Customize colors and export as PNG.
Detect the tempo (BPM) of any audio file. Includes tap tempo feature and genre reference guide.
Trim, cut, and slice audio files with interactive waveform visualization. Drag handles to select portions, use keyboard shortcuts, zoom and pan, preview selection before export. Supports MP3, WAV, OGG, AAC.
A lecture recording is too slow to review and you want 1.5× without chipmunk pitch.
Input
lecture.mp3 · 1.5× · preserve pitch
Output
A 1.5× file at the original pitch, natural voice, shorter runtime
Time-stretching changes duration without resampling, so the pitch stays natural instead of rising like a sped-up tape. Decoupling speed from pitch is exactly what makes faster review listenable.
Speed up or slow down audio playback without changing pitch, or change both speed and pitch together. Drag the speed slider from 0.25x to 4x and hear the result immediately. Great for transcription work, language study, music practice, or fitting audio into a specific time window.
Load the episode, turn on Preserve Pitch, and pick 1.5x. The download is time-stretched via 2048-sample Hann-windowed grains so the runtime drops to duration/1.5 while voices keep their natural pitch. Note the in-page preview will still sound slightly higher because preview uses tape-style playbackRate; trust the downloaded MP3.
Set 0.5x with Preserve Pitch on to roughly double the duration while keeping pitch, staying inside the clean 0.5x-2x window where grain warble stays minimal. Leave Preserve Pitch off if you want the deliberate slowed-down, lower-pitched tape sound instead.
Slow down fast speech to catch every word while typing.
Reduce playback speed on foreign-language audio to better follow pronunciation.
Slow a difficult passage down to practice at a comfortable tempo before building back up.
Speed up a voiceover slightly to fit a fixed video duration without re-recording.
The Audio Speed Adjuster decodes your uploaded file with the Web Audio API's decodeAudioData and lets you set a speed from 0.25x to 4x on a slider (step 0.05), with one-tap presets at 0.5x, 0.75x, 1x, 1.25x, 1.5x, and 2x. It offers two genuinely different processing paths depending on the Preserve Pitch toggle. With pitch preservation OFF, it does straight resampling: the output buffer length is the original length divided by the speed, and each output sample is read back from the source using 4-point cubic interpolation for smoother results. Because this is a pure resample, pitch tracks speed exactly like fast-forwarding or slowing down tape, 2x raises everything an octave (the 'chipmunk' effect) and 0.5x drops it an octave, while the duration shrinks or stretches proportionally.
With Preserve Pitch ON, the tool runs a granular overlap-add time-stretch (a simplified WSOLA-style approach) so the running time changes but the pitch is held. It slices the signal into 2048-sample grains, multiplies each grain by a Hann window (0.5 * (1 - cos(2pi i / 2048))), and overlap-adds them onto the output at a hop of 512 samples (windowSize/4, i.e. 75% overlap), advancing the read position by hop x speed each step; a final pass normalizes the channel so the summed grains do not clip. This algorithm is honest about its limits: at extreme stretch ratios the grain boundaries beat against sustained tones (audible warble/phasiness) and soften transients like drum hits, so it sounds cleanest when you stay within roughly 0.5x-2x. One important behavioral note: the in-browser Preview always plays through an AudioBufferSourceNode with playbackRate set to the speed, which is the tape-style path, so the preview is pitch-shifted even when Preserve Pitch is enabled. Pitch preservation is applied only to the rendered download.
Output is always exported as MP3, encoded with lamejs at 192 kbps, and the filename encodes the settings (for example speed-1.5x-pitch-preserved-yourfile.mp3 or speed-2x-yourfile.mp3). The interface shows a live duration comparison (original time versus the new time = duration / speed) and a percent-faster/slower readout, plus a preview volume slider (0-100%) that affects only the in-page preview, not the exported file. All decoding, stretching, and MP3 encoding run client-side in the browser. Practical ratios: 0.5x for careful transcription, 0.7-0.8x for language-listening practice, and 1.25x-1.5x for speeding through podcasts and lectures with Preserve Pitch on to keep voices natural.
With pitch preservation enabled, the pitch stays the same regardless of speed. With it disabled, pitch rises when sped up and drops when slowed down, like a tape machine.
Time-stretching algorithms introduce artifacts at very low or very high ratios. Staying within 0.5x-2x produces the cleanest results.
This tool applies a uniform speed change. To adjust only a section, trim it first, change speed, then merge it back.
Audio is decoded and processed locally with the Web Audio API. Your files are never uploaded to a server.