Why does the pitch move at all?

Because playing a recording faster means reading its samples at a different rate, which squashes the waveform in time and multiplies every frequency by the same factor. Speed and pitch are two views of one operation whenever resampling is involved.

Can I change speed without moving the pitch?

Yes, by time stretching rather than resampling. A stretcher rebuilds the audio from overlapping grains so the duration changes while the frequencies stay put. That is a different operation from the one this calculator quantifies, and it is what the keep-pitch mode of the speed changer does.

Why is doubling speed exactly one octave?

Because an octave is a factor of two in frequency, and doubling the speed doubles every frequency in the material. Twelve semitones also describes a factor of two, which is why the arithmetic has such a clean anchor point.

Is a small speed change safe to use on music?

Up to a few percent the pitch shift is small enough that many listeners would not notice without a reference, and it is a common trick for making a track sit at a slightly different tempo. Beyond that the key change becomes the dominant effect, and a stretcher is usually the better tool.

How do I know which approach was used on a file I did not make?

Listen to whether the pitch and the speed agree. If the material has moved in tempo and its key has moved with it, it was resampled; if the tempo changed and the key did not, it was stretched. There is no way to tell from the file contents alone, only from the relationship between the two.

Playback Speed Calculator

You Might Also Need

Audio Speed Changer

Change playback speed, with or without pitch change

Time Stretcher

Stretch or compress audio duration

Pitch Shift Calculator

Calculate semitone shifts

Tempo Changer

Adjust tempo while preserving pitch

Playback Speed Calculator works out the speed needed to turn one duration into another, and how far the pitch moves as a consequence. It quantifies the coupling between speed and pitch that tape-style playback produces.

What is Playback Speed Calculator?

Enter the original and target durations and the panel gives the speed required, the resulting pitch shift, and the new duration.

The inputs and the three results:

An original duration in seconds from a tenth to twenty hours.
A target duration over the same range.
A speed figure as a multiplier to four decimal places.
The pitch shift in semitones, signed to two decimal places, which is what the speed change would do to the pitch.
The resulting duration, confirmed from the ratio.

A block below restates the arithmetic for the common cases. One and a quarter times speed works out to about four semitones up and three quarters speed to about five semitones down, doubling speed raises the pitch by exactly an octave and halving it drops the pitch by an octave. Those figures are all the same relationship: speed and pitch move together in direct proportion when material is played at a different rate, because playing a recording faster is the same operation as resampling it, and resampling compresses the waveform in time and therefore multiplies every frequency by the same factor. The semitone figure comes from taking the logarithm of the speed in base two and multiplying by twelve, since an octave is a factor of two and contains twelve semitones, which is why a doubling comes out to exactly twelve and everything else falls between. The tool is explicit that this describes tape-style behaviour only. Changing speed without changing pitch is time stretching, which is a different operation entirely and is what the speed changer's keep-pitch mode does. Knowing which of the two applies before choosing a tool is the practical value here, because a speed change that was intended to be transparent will produce a very audible pitch shift if it is applied by resampling instead of by stretching.

What it does not do:

It processes no audio, so nothing is rendered.
It assumes a constant speed across the whole file.
No time-stretching arithmetic, since that is a different operation with no pitch consequence.
No formant or timbre considerations for large stretches.
No handling of a speed that varies over time.
Nothing is uploaded, and no history is kept.

Use it before applying a change: to see what a speed-up will do to the key of a track, to work out whether the pitch consequence is acceptable, or to decide between resampling and stretching. When the speed change has to be applied to real audio, the audio speed changer offers both the tape-style and the pitch-preserving modes, and the time stretcher covers the duration case alone. When the pitch shift rather than the speed is the thing being quantified, the pitch shift calculator approaches the same relationship from the pitch end. The arithmetic is worth running before any change is applied rather than after, because the pitch consequence is not something that can be corrected in the result without a second operation: a track resampled up by four percent has already lost its original key by the time anyone hears it.

How to use Playback Speed Calculator

Enter the duration the material has now.
Enter the duration it needs to become.
Read the speed multiplier and the pitch shift in semitones that would follow.
Decide whether that pitch consequence is acceptable, or whether a time-stretch is needed instead.

When to use Playback Speed Calculator vs related tools

Playback Speed Calculator is the tool for seeing the pitch cost of a speed change before committing to it. Audio Speed Changer applies the change with either the tape-style or the keep-pitch behaviour, and Time Stretcher handles the duration without touching pitch. When the pitch consequence itself is the subject, Pitch Shift Calculator works from that end of the same relationship.

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.