A linear fade changes the level by the same amount every moment; a logarithmic fade changes it by the same number of decibels every moment. On long fade-ins and fade-outs, a logarithmic or S-shaped curve sounds smooth, while a linear fade-out seems to stay loud and then drop suddenly at the end. For very short fades that remove clicks, linear is the right choice, and for crossfades between two different tracks, an equal-power curve keeps the loudness steady.
In Short
The short version:
- Linear: even change in level; best for fades of a few hundredths of a second.
- Logarithmic: even change in decibels; sounds steady on long fades.
- S-curve: gentle start and end; a safe all-round choice for music.
- Crossfading two different tracks: equal power, to avoid a dip in the middle.
- Crossfading two takes of the same recording: linear (equal gain), to avoid a bump.
Why the Shape of a Fade Matters
A fade is a gradual change in volume, and the curve describes how that change is spread over time. Curves sound different because we do not hear level in equal amounts but in ratios. That is why audio levels are measured in decibels, and, as the School of Physics at UNSW Sydney explains , a change of about 10 dB is heard as a doubling or halving of loudness, whatever the starting level.
Take a 10-second fade-out. With a linear curve, the level is still at half after 5 seconds, and half the level is only 6 dB down, which the ear hears as slightly quieter. The level reaches -20 dB, where the music really sounds distant, only in the last second. The result: the track seems to carry on at almost full volume and then vanish. A curve that falls evenly in decibels spreads the change across the whole fade.
The Main Fade Curves
Linear
The gain moves in a straight line between silence and full level. Over long fades it sounds uneven, for the reason above: a fade-in appears to arrive quickly and then barely change, and a fade-out appears to end abruptly. Over a few hundredths of a second the ear cannot follow the shape at all, and a straight line is the cleanest way to bring a waveform to zero.
Logarithmic
The level changes by the same number of decibels every second. To the ear the loudness rises or falls at a constant rate, which makes this the natural choice for a long fade-out at the end of a song or a slow fade-in of background music. Editing programs differ in how they name these curves; some call the same shape exponential. If in doubt, listen: the right curve is the one where the change sounds even.
S-Curve
An S-curve starts slowly, changes fastest in the middle and eases out again. It avoids both an abrupt start and an abrupt end, so it is a dependable default for music when you don’t want to think about the choice.
Which Curve for Which Job?
| Situation | Curve | Typical length |
|---|---|---|
| Removing a click at a cut | Linear | 0.01–0.05 s |
| Start or end of a spoken segment | Linear or S-curve | 0.5–1 s |
| Song ending with a fade-out | Logarithmic or S-curve | 3–10 s |
| Background music fading in under a voice | Logarithmic | 2–5 s |
| Crossfade between two different songs | Equal power | 2–6 s |
| Crossfade between two takes of the same recording | Linear (equal gain) | 0.01–0.1 s |
Crossfades: Equal Gain vs. Equal Power
A crossfade plays the end of one clip and the start of the next at the same time, fading one out while the other fades in. Here two curves are added together, and what matters is their sum.
Equal Gain (Linear)
With two linear fades, both clips are at half level in the middle, and the two gains always add up to 1. If the clips contain the same material, for example two takes of one recording joined at an edit, their waveforms add up exactly and the level stays constant. If they are different songs, their waveforms do not line up, the combined power in the middle is about 3 dB lower, and you hear a dip.
Equal Power
An equal-power crossfade uses curves shaped like a quarter of a sine wave, so each clip is at about 71 percent (-3 dB) in the middle and the combined power stays constant. For two unrelated pieces of music this sounds perfectly even. Used on identical material it would do the opposite and create a 3 dB bump. Despite what is often written, equal power is not a logarithmic curve; it is a shape of its own, designed for adding two signals.
How to Apply These Curves
All three situations can be handled in your browser.
Step 1: Fade a Single File
Open the recording in the Audio Fade Tool, enter the fade-in and fade-out lengths and choose Linear, Logarithmic or S-curve. The listen buttons play each fade, so you can compare the curves by ear.
Step 2: Crossfade Between Files
Add your files to the Audio Joiner & Mixer, choose Smooth fade between them and set its length. It uses an equal-power curve, which suits transitions between different songs. For spoken segments, leave it at No transition.
Step 3: Remove a Section Without a Click
When you cut a part out of a recording with the Audio Trimmer, the two sides are joined with a 10-millisecond linear crossfade, the right curve for joining identical material.
Try the Curves Yourself
Open a song in the Audio Fade Tool and switch between the three curves on the same fade-out.
Open the Audio Fade ToolFree, no sign-up, and your files never leave your device.