Audio Fades

On one clip

The easiest way to make audio volume fade in or out is to right click the clip, and from the Preset Menu, choose from a selection of fade ins and fade outs.

An alternative more flexible method for fade in/out is to set Volume keyframes manually, which allows you to choose a duration for the fade. The default setting gives you a linear fade, that is, the volume changes at a constant rate. You can optionally set the interpolation type, for example:

  • Ease In/Out (Sine), which you might find gives a smoother more natural fade.

  • Ease Out (Expo), which allows the signal to die away more slowly at the end.

At a transition between two clips

OpenShot transitions do not currently include audio crossfades. At the overlap of two clips, the audios are simply added together.

You must therefore set any volume changes yourself, either using the Preset menu or (usually) by inserting volume keyframes manually. If you use the Preset menu then the transition should usually be the same length as the audio fades you apply.

It might help to place the audios onto separate tracks (Seperate Audio using the Preset menu) before you work on it, though this is not necessary.

One method to set an audio crossfade is:

  • Select the second clip, and navigate to its start. Set its Volume to 0.

  • Select the first clip, and insert a Volume keyframe.

  • Navigate to the end of the first clip. Set the clip’s Volume to 0. Set the interpolation type if desired.

  • Select the second clip, and set the Volume to 1 (or to the target value for the clip). Set the interpolation type if desired.

If you do not set the interpolation type the fade will be linear, which is suitable for many purposes. The linear setting is a type of “constant gain crossfade”, and there should be no clipping of the signal during the transition.

At an advanced level, note that the perception of audio volume can be represented as the sum of the squares of the two clip volumes. Plotting that sum (the scaled red line) for a linear crossfade we get:

_images/linear-crossfade.png

The horizontal axis shows time, and the vertical axis is perceived audio volume.

There is a perceived dip in audio power, which is often desirable help the ear adjust to the new sound track.

A smoother dip is given when the interpolation types for fade out and fade in are both set to Ease In/Out (Sine):

_images/sine-dip-crossfade.png

This is also a type of “constant gain crossfade”, and there should be no clipping of the signal during the transition.

There are circumstances, for example if two music audio clips have some correlation, where you might wish a “constant power crossfade”, given by interpolation types Ease Out (Sine) at step 3 and Ease In (Sine) at step 4:

_images/constant-power-crossfade.png

There might possibly be some peak clipping of the signal, unlike with the “constant gain crossfades” above.

You could also choose to fade the audio completely out before bringing it back in, by using an extra keyframe in the middle of the transition.

Sometimes a video director will choose to have the sound and the video change at different times. This is known as a “split edit”, and can help with continuity – for example to avoid a sense of a tennis match in a conversation between two people.

The choice of audio fades is for you to decide, as you see fit.