What is the difference between this and the speed changer?

This tool only ever changes duration, so the pitch comes out where it started. The speed changer offers both behaviours: a tape mode that resamples and moves pitch with speed, and a keep-pitch mode that works like this one. If the pitch must not move, the two are equivalent.

How far can I push the change before it sounds wrong?

Around fifteen percent in either direction is where most material stays convincing. Beyond that the grains have to be positioned further from where they naturally continue, and attacks start to lose their edge. Percussion shows it first and sustained material last.

Do I need to know the original tempo exactly?

Only if you want a specific target figure. Because the tool uses the ratio between the two numbers, an error in both cancels out; if you are unsure, an original of a hundred and twenty and a target of a hundred and thirty two gives the same ten percent change as any other pair in the same proportion.

Does the tempo change affect the pitch at all?

No. The audio is rebuilt from overlapping grains rather than played at a different rate, so every frequency ends up where it began. That is precisely why the method is slower than a resample, which would need no search at all.

Can I change tempo gradually across a file?

There is one ratio for the whole file, so the change is proportional and constant. For a recording that drifts, split it at the points where the tempo changes, process each part with the ratio it needs, and join the results with the joiner.

Tempo Changer

You Might Also Need

Time Stretcher

Stretch or compress audio duration

Audio Speed Changer

Change playback speed, with or without pitch change

BPM Calculator

Calculate beats per minute from taps

Audio Speed Slow Down

Slow audio for comprehension

Tempo Changer speeds a recording up or slows it down while the pitch stays exactly where it was. Give it an original and a target tempo and it works out the ratio, or drive it directly with a percentage.

What is Tempo Changer?

Load a file, choose whether to work in tempo or in percent, and process. The report states the ratio, the two tempos or the percent, the duration before and after, and confirms that the pitch was preserved.

The controls:

A pair of mode buttons, one for tempo and one for percent.
In tempo mode, an original and a target tempo from twenty to four hundred beats per minute, defaulting to a hundred and twenty and a hundred and twenty four.
In percent mode, a single slider from fifty to two hundred percent, defaulting to a hundred.
A report line with the ratio, the duration change and the note that the pitch was preserved.

The arithmetic is deliberately small. In tempo mode the BPM ratio is the target divided by the original, protected against a zero original so a slip of the keyboard cannot produce an infinite ratio; in percent mode the ratio is simply the percentage over a hundred. A faster tempo means a shorter file, so the stretch factor handed to the engine is the reciprocal of the ratio. The engine itself is a windowed overlap-add method in the WSOLA family: the audio is cut into overlapping grains, each output grain searches a short range of positions for the one that best continues the waveform already written, and the search is what keeps pitched material from turning into a comb-filtered mess. Because the grains are recombined at new positions rather than played faster, the pitch and the timbre survive intact — this is a time operation, not a speed operation. The honest limit is the same one any such method has. Within roughly fifteen percent in either direction the change is hard to hear; beyond that transients begin to soften and percussion loses some of its snap, because a grain-based method reconstructs attacks rather than moving them. Both modes are pure functions of the samples and the ratio, so the same file and the same setting always produce the same output.

Where it struggles:

Extreme changes smear transients, so a very large tempo move is best reserved for material without sharp attacks.
No independent pitch control, because holding the pitch is the entire point here.
Nothing about groove is analysed, so the result is a proportional change rather than a tempo map.
One ratio applies to the whole file.
No formant handling, so a large stretch on speech can sound odd even with the pitch intact.
Output is sixteen bit WAV, and up to two channels are processed.

Use it when a take sits at the wrong tempo for an edit, when a practice recording should be a little slower to follow, or when a demo needs to be heard at performance speed. When the pitch should move with the speed instead, the speed changer's tape mode does that by resampling. When the same job is stated as a length rather than a tempo, the time stretcher says it in different units. Reading the reported ratio before and after is the quickest way to confirm what a change implies, since the duration movement appears on the same line as the setting that produced it.

How to use Tempo Changer

Drop an audio file onto the panel and note the duration shown.
Choose to work by tempo or by percent, depending on how the problem is stated.
Enter the original and target tempo, or move the percent slider.
Press process, read the reported duration change, and download the result.

When to use Tempo Changer vs related tools

Tempo Changer is the tool when the tempo is the thing being named, which is how a musician usually states the problem. Time Stretcher handles the same job from a length-first point of view, and Audio Speed Changer adds a tape-style mode where the pitch moves with the speed. To find the tempo of a file you already have, BPM Calculator and Tap Tempo measure it before you change anything.

Privacy & Security

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