… for Codecs & Media

Tip #1325: Why Is an Audio Fade Called +3 dB?

Larry Jordan – LarryJordan.com

Audio is a Strange Beast

Unlike video, audio levels are logarithmic. For example, whenever the audio level increases (or decreases) 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 add this “bump,” the cross-fade would sound fainter in the middle of a transition, then louder at each end.

When fading to or from black, a straight-line (linear) transition is best. When cross-fading between two clips, both of which have continuous audio, a +3 dB transition will sound better.

EXTRA CREDIT

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.

Still, the general rule of audio is: Whatever sounds the best to you IS most likely the best.