Disolving two sound together

Question

What is the best method to disolve two sound together on one sound timeline?
Dan

Answer 1

It depends on (a) whether the sounds are fairly nondescript, e.g; just people chattering, (b) how closely they must be kept "in sync" (synchronised, in step) with the video, (c) if the sounds came into iMovie separately from the video, etc.
Here's an example: if you have two video clips, complete with sound, of people chattering, you can simply add a Cross Dissolve transition between those two video clips. The sound will dissolve, too.
But when you add a Dissolve of, say, three seconds between two video clips, then the first three seconds of the 2nd video clip and the first three seconds of sound on that clip will disappear, or get used up, in the Dissolve. So if there's something important at the start of the 2nd clip you may need to use a very quick Dissolve, so that not too much of it gets "eaten away" when it's laid on top of the last second(s) of the 1st clip.
A better way is to select the video clips which you may be going to dissolve between, and then use "Advanced" and "Extract audio" to 'Extract' the audio from those clips before doing any dissolving.
['Extracting' the audio just makes a copy of the audio and puts it in an audio track beneath the video, and 'Locks' the audio to its parent video clip. The original audio within the video clip still remains, but it's automatically muted down to zero volume level.]
You can then adjust the separate audio as much as you want by selecting an audio clip, clicking on "View" and "Show Clip Volume Levels", and then you can click on any part of the straight-line volume level, within an audio clip, to "anchor" the level, then drag it down to whatever you want.
(..It's all described in Apple's online iMovie audio-editing Help here, as part of all the other iMovie Tutorials here..)
By sliding two audio clips closer together, or even overlapping them, you can create a smooooth transition from one audio clip to the next. But dragging an audio clip may drag it "out of sync" with its parent video clip. You may have to decide if it's OK or not to 'lose' some video if you pull it in closer towards a previous clip, so as to keep it in sync with the audio dissolve you've made.
You might decide to 'insert' some extra bit of video (..a 'cutaway' shot..) and then shorten that so that the region of video which you do want to keep will stay in sync with your audio after you've made an audio dissolve.
Here's a little 'thumbnail image' of how you can adjust the volume of two 'Extracted' audio clips by altering their audio levels:
To see it more clearly, click here and then click on the 'Start Slideshow' button.
(..The picture shows two video clips, Original Clip A and Original Clip B. Just before creating a transition between them, think how long you want the transition to be, say two seconds, and then cut the two clips at a bit more than two seconds from their ends, making Sub-clip A and Sub-clip B.
Then Extract the audio from those two sub-clips. To make things easier, drag one of the audio clips onto the lower audio track.
The audio clips are now isolated from the video clips. Apply your Dissolve, or whatever, to the two video Sub-clips.
Adjust the levels of the two audio clips to get the perfect dissolve..)