Audio Fade In/Out

Add fade-in and fade-out effects to audio files with adjustable duration.

Tested tool guide Tested browser tools Checked August 16, 2026

What Audio Fade In/Out does, with a checked example

Load an audio file, choose a fade-in length, a fade-out length, or both, and download a new copy whose gain ramps from silence up to full level at the start and back down to silence at the end. Processing happens entirely in the browser, so nothing about the recording leaves the machine. The thing people get wrong first: the fades are anchored to the file's boundaries, not to where the sound actually starts and ends. A file with trailing silence gets a fade-out that happens partly inside that silence, and the audible content can still end with a click.

Worked example

A concrete input and expected output from the current implementation.

Input

File: interview.mp3, duration 30 s. Fade-in: 2 s. Fade-out: 3 s.

Expected output

A 30-second file whose gain starts at zero, rises to full level by the 2-second mark, stays at full level from 2 to 27 seconds, and falls back to zero by the 30-second mark. Length, sample rate, and channel count are unchanged.

A fade is a gain ramp anchored to the file's boundaries: the fade-in occupies the first 2 seconds (0-2 s) and the fade-out the last 3 (27-30 s), leaving 25 seconds of unmodified audio between them.

How the result is produced

Gain envelope

A fade is a per-sample volume curve applied to the whole file. Every sample is multiplied by a gain that starts at zero, rises to full level across the fade-in duration, holds there, then falls back to zero across the fade-out duration. Because this only scales amplitudes, the output keeps the input's exact length, sample rate, and channel layout - nothing is cut, shifted, or resampled.

Fade curve and output format

The shape of the ramp between zero and full matters to the ear. A linear ramp is simplest to compute, but a linear fade-out sounds as if it drops quickly and then lingers; an equal-power (cosine) curve keeps perceived loudness steadier. Whichever curve is used, the output is a new audio file, so a lossy input such as MP3 must be decoded, processed, and re-encoded - a second lossy generation.

Good uses

Take the edge off a raw recording - a podcast clip, a phone interview, a field capture - so it opens gently instead of slamming in at full level and closes without a click.
Build a background music bed: fade the music in under a narrator and out at the segment boundary so it sits beneath the mix instead of punching in and out.
Smooth the splices when stitching clips of different loudness into a collage, demo, or showreel, since each fade masks the level jump at the join.

Limits and checks

The output is never shorter than the input. A fade lowers levels; it does not remove audio, so the first seconds of a fade-in are still in the file, just quieter. If a start sounds missing, what you hear is the reduced level - shorten the fade rather than assuming the audio was cut.
If fade-in and fade-out durations together exceed the file's length, the two ramps collide in the middle and cannot both behave as specified. How the overlap is resolved is worth verifying on a short test clip before applying it to a file you care about.
A lossy source (MP3, M4A) comes back re-encoded, and the extra lossy generation can add audible artifacts on quiet fades. For a master you plan to keep, run the fade on the lossless source (WAV, FLAC) and encode from that.

Common questions

Why does my fade-out seem to happen during silence?

Because the fade is anchored to the end of the file, not to the end of the sound. Any trailing silence - a pause after the last word, long room tone - sits between the content and the end of the file, so the gain starts falling while the audio is already quiet. Trim the tail before fading, or shorten the fade to fit the content.

Why does the fade sound like it dips in the middle?

The ramp's shape, not the fade itself, controls how it sounds. A linear gain ramp drops quickly in perceived loudness and then lingers, which can read as a dip; an equal-power (cosine) curve keeps perceived level steadier. If a fade sounds lumpy, it may be the curve the tool uses - there is usually nothing wrong with your file.

References and verification

The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.