What is the difference between the two modes?

Tape style resamples the waveform, so the duration and the pitch both change by the same factor, the way a record does when its speed is altered. Keep pitch stretches the time axis without moving the frequencies, by overlapping short grains so that the audio is reconstructed rather than played faster.

Why is the keep-pitch mode slower to run?

Because every output grain searches a range of positions for the one that best continues the audio already written, and that search costs roughly a second of processor time per minute of audio. Tape style has no search at all, so it is essentially instant.

What does airy mean in the keep-pitch description?

It is the sound of overlapping grains: on large stretches the repeated and blended portions add a soft, slightly hollow quality to sustained material. Small changes are usually inaudible; doubling or halving the duration is where it becomes noticeable, especially on voices.

Does the factor of one change anything?

No, both modes return a copy of the input unchanged at a factor of exactly one, which is why the slider defaults there. It is a useful reference point: set the factor, process, and compare against the preview of the original.

Which mode should I use for a music bed under a voice?

Keep pitch, because moving the pitch would clash with the voice and change the key of the music. If the result sounds airy, changing the factor by a smaller amount and taking two smaller steps is usually better than one large stretch.

Audio Speed Changer

You Might Also Need

Audio Speed Slow Down

Slow audio for comprehension

Tempo Changer

Adjust tempo while preserving pitch

Time Stretcher

Stretch or compress audio duration

Playback Speed Calculator

Calculate speed change ratios

Audio Speed Changer alters playing speed either the way a tape deck does, with pitch following the speed, or with the pitch held steady. Both modes take a factor from a quarter speed up to four times.

What is Audio Speed Changer?

Choose a mode, set the factor with the slider or one of the presets, and process. The output has a duration of the original length divided by the factor, so a factor of two halves the file and a factor of half doubles it.

The modes and controls:

Tape style, where speed and pitch move together: below one the audio slows and drops in pitch, above one it speeds up and rises, exactly like a record player.
Keep pitch, where the duration changes but the pitch stays roughly where it was, at the cost of some airiness on large changes.
A factor slider from a quarter to four, in steps of a twentieth, defaulting to one.
Five presets at half, three quarters, one and a quarter, one and a half and two times.

The two modes are genuinely different pieces of arithmetic. Tape style resamples the signal: output frame k reads the input at k times the factor with linear interpolation between neighbouring samples, which compresses or stretches the waveform itself and therefore moves every frequency with it — that is why the pitch changes. Keep pitch instead stretches time without moving pitch, using a windowed overlap-add method with a search that keeps grains aligned: each output grain searches a small range of lags for the position whose onset best continues the audio already written, which is what stops tonal material from comb-filtering into a phasey mess. The search costs about a second of processor time per minute of audio, which is the reason a long stretch takes noticeably longer than a speed change. Both modes size their outputs so the duration arithmetic holds, and both are pure functions of the samples, so the same file and factor always produce the same result. The difference between the modes is worth holding on to when choosing one: tape style changes speed and pitch together because it rewrites the waveform on a different time base, while keep pitch changes only the duration by reconstructing the audio from overlapping grains. The search that aligns each grain is a WSOLA-style pass: every output grain tests a small range of offsets and keeps the one whose samples best continue what has already been written, which is what stops tonal material from turning phasey. Both divide the source length by the factor, so a half-speed pass doubles the file and a double-speed pass halves it.

What the tool does not do:

Large keep-pitch changes sound airy, because the method repeats and overlaps short grains rather than resynthesising.
No independent pitch control: the pitch-shifter is the tool for changing pitch at constant speed.
One factor applies to the whole file, with no tempo map or gradual change.
No presets above two times, although the slider reaches four.
No formant handling, so a large keep-pitch stretch on speech can sound unnatural even though the pitch holds.
Output is sixteen bit WAV, and each channel is processed independently, which keeps a stereo file aligned but does not preserve any stereo technique that depended on the original timing.

Use it when a recording needs to be longer or shorter: fitting a piece of audio to an edit, making a rehearsal recording easier to follow, speeding up a slow take to hear how it would sit, or slowing something down to transcribe a phrase. When only the pitch should move, the pitch shifter does that independently, and when a file simply needs to be slower for comprehension without any pitch judgement, the accessibility-oriented speed tool takes the narrower range.

How to use Audio Speed Changer

Drop an audio file onto the panel.
Choose tape style if the pitch should move with the speed, or keep pitch if it should not.
Set the factor with the slider or one of the five presets.
Press process, then compare the previews and download the result.

When to use Audio Speed Changer vs related tools

Audio Speed Changer is the general speed tool, with both the tape-style and pitch-preserving modes and a range from a quarter to four times. Tempo Changer and Time Stretcher approach the pitch-preserving case from specific angles, and Pitch Shifter moves the pitch at constant speed instead. For simply slowing speech for comprehension, Audio Speed Slow Down covers that narrower job. For the slowed-and-reverbed remix treatment, Slowed + Reverb / Nightcore applies the same speed change with those additions built in.

Privacy & Security

This tool runs entirely in your browser — no data ever leaves your device. There is no server round-trip, no upload, no logging, and no account required. Your input is processed locally using client-side JavaScript and is never stored, transmitted, or accessible to anyone else. When you close the tab, everything disappears.