… for Codecs & Media
Tip #104: Why Is a Smooth Audio Fade Called +3 dB?
Audio is a Strange Beast
Unlike video, audio levels are logarithmic. For example, whenever the audio level increases (or decreases) by around 10 dB, the perceived volume is doubled (or cut in half). These log values also have an impact in cross-fading between clips.
A +3 dB transition adds a 3 dB increase in volume to both clips in the middle of a cross-fade. If the software did not, the audio would sound like it is getting fainter in the middle of a transition, then louder at the end.
When fading to or from black, a straight-line (linear) transition is best. When cross-fading between two clips, both of which have audio, a +3 dB transition is best.
Some software allows you to change the shape of the curve manually. These rules still apply, but manual adjustments allow much greater control over how the transition sounds.
The general rule is: Whatever sounds the best to you IS the best.