9) Fade in and fade out

Fade in and fade out

When Fade-In is applied to a selected audio, it will gradually increase the sound from silence to its original volume. A fade in is often applied over a very short audio selection (less than a second).

The shape of the fade is linear, so it appears as a straight line from beginning to end (when viewed in the default linear Waveform View Mode). The speed of the fade-in depends entirely on the length selected for the fade. Lets take the below audio clip.

To do a fade-in, select the portion of audio that you would like to fade-in using the selection tool.

Then go to Effect > Fade In.

The result would be seen as given below:

You may get a more "musical" result by applying a linear fade in three times to the same audio selection.

Fade-Out

When Fade-out is applied to a selected audio, it will gradually decrease the sound from its original volume to silence. A fade out is often applied to a longer selection than a fade in, typically to a selection up to about ten seconds long.

To do a fade-out, select the portion of audio that you would like to fade out using the selection tool.

Then go to Effect > Fade Out.

The result would be as given below:

Cross fading

We create a cross fading effect when we want smooth transitions between two events (tabla and violin as two events; end of song and cheering of crowd). A crossfade is essentially both fade out and fade in occurring simultaneously to two separate tracks. The first track slowly fades out and the second fades in.

Many songs use fading techniques to great effect when starting or ending, or at particular parts in the song. The same goes for video; it’s useful to be able to fade into a crowd’s cheer, or fade out of an original audio source in favor of narration of some kind. Crossfading is valuable because it allows these changes to happen quickly without being jarring, without introducing silence, and while sounding smooth and more natural. DJs often use this technique while matching beats of two different songs to produce a continuum of sound, while editors often use crossfades (as well as fade-ins and fade-outs) to make the introductions of different sound components sound less “sudden”and more natural. (Source: http://manual.audacityteam.org/o/man/fades.html#crossfade)