Change speed & volume

Speed and pitch

Speeding the audio up makes it shorter and raises the pitch slightly ("chipmunk" effect); slowing it down does the opposite. It's handy for fun effects, making a voice memo quicker, or slowing a musical passage down to study it.

Watch the volume

Raising the volume above 100% can add distortion if the audio was already loud. If you hear crackling, lower it a bit: a clean volume beats a clipped track. To know how many dB to raise it by, measure it with Video loudness (LUFS).

Why changing speed also changes the voice

Speeding up audio means running the samples faster, and every frequency rises with them: the voice becomes higher, like old 45 rpm records played at 78. It is the effect you always hear when speed and pitch stay tied together, and it is what this page does.

The link can be broken by a different process, time stretching, which lengthens or shortens the audio in small pieces while holding the pitch: it is what podcast players use to play at 1.5x without turning everyone into a cartoon. It costs far more to compute and, pushed beyond a certain point, introduces a recognisable metallic timbre.

How far speech can be sped up

Comprehension holds well up to about 1.5 times normal speed; between 1.5 and 2 the brain adapts within minutes if the speech is clear and well recorded; beyond 2.5 comprehension collapses for almost everyone, and that is not a matter of habit but of how long it takes to tell consonants apart.

Two things move that threshold. The material: slow, well-articulated speech takes far more than overlapping conversation or a foreign language. And the kind of listening: to follow a lecture you need to understand, you go slower than to revisit something you already know.

Slowing down, and what it is really for

Slowing down is the tool of anyone learning a piece of music: taking a solo to half speed lets you hear the individual notes, and only afterwards does the hand learn them at the right tempo. It also serves for transcribing a difficult interview, and for understanding a foreign language spoken fast.

Slowed down a great deal, though, audio starts to sound swollen and smeared: below half the original speed the flaw is obvious with any method. For musical study it is better to go down in steps, stay at the highest value where the passage is still clear, and climb back up gradually.

Volume, and the limit that cannot be passed

Raising the volume above a hundred per cent adds no information: it multiplies the samples, and those exceeding the maximum that can be represented are clipped flat. The result is a dry distortion that cannot be removed afterwards, because the original data is gone.

If audio is too quiet overall, the right route is not raising it until it distorts but normalising, that is bringing the highest peak to the maximum and scaling everything else in proportion. And if the problem is that loud and quiet parts are too far apart, then a compressor is needed, which is another thing and belongs to an editing program.

Nearby tools

To trim a section there is Audio trimmer, to put several together Merge audio and for format Audio converter. To measure how loud a track really is there is Video loudness, and for the audio inside a clip Extract audio from video.