You trim a music or podcast clip and, on playback, the start or end has a sharp click, like a small "pop". It's not a broken file: the waveform gets cut at a point that isn't zero, and that abrupt voltage jump is what the speaker reproduces as a click. Fade in and fade out fix this by smoothing the volume from and into silence.
What a fade actually is
A fade in raises the volume gradually from silence to normal level over the first seconds of the clip. A fade out does the opposite at the end: it lowers the volume gradually to silence instead of cutting it abruptly. Internally, each audio sample gets multiplied by a curve going from 0 to 1 (or 1 to 0), instead of leaving the volume fixed right up to the cut.
Why a cut without a fade sounds bad
When you trim an audio clip, it's very rare for the cut point to land exactly on a zero-crossing of the waveform (the instant the signal is exactly 0). If the cut lands anywhere else, there's an instant voltage jump between "mid-wave sound" and "total silence" — that jump is exactly what the ear perceives as a click or pop. A fade, even a short one of 20-50 milliseconds, removes the jump because the transition passes through every intermediate value.
How long each fade should be
There's no universal number, but as a reference:
- Music that starts at full intensity (a podcast intro, for example): 1-2 seconds of fade in prevents it from sounding like it "explodes" at the start.
- Short clips trimmed from a song or interview to share: 0.3-0.5 seconds of fade on each end is usually enough to remove the click without it reading as an obvious effect.
- The end of a full podcast episode: 2-4 seconds of fade out, so the closing music dies away naturally instead of cutting abruptly.
Each fade (in and out) is independent: you can enable just one of the two, or both with different durations.
Frequently asked questions
Why do I hear a "click" when trimming audio even without touching the fades? Because the cut point landed at a moment where the wave isn't at zero. Applying a short fade at that edge, even a fraction of a second, fixes it.
Does the fade affect the whole clip or just the edges? Only the configured edges; the rest of the audio keeps its volume unchanged.
Can I apply only a fade out without a fade in? Yes, each one is enabled or disabled independently.
Is it processed in my browser? Yes, with FFmpeg compiled to WebAssembly, with nothing uploaded to any server.
Smooth out the start and end of your audio with audio fade in/out, with adjustable duration for each fade, 100% in your browser.