Working with sound adds a whole other element to animation. Since the timing of animation can be controlled precisely within the fraction of a second it can be synced perfectly with both speech and music.
First, we covered lip sync. Lip sync can be done simply by breaking down dialogue into the individual sounds that occur during each frame. Then, the mouth shape is drawn to match the specific sounds. Mouths shapes are covered in too many books in too many different ways for me to go into detail here. It is slightly more complex in practice since multiple syllables can occur quickly in a single frame. The important thing in making a mouth look convincing is to open quickly on the vowels and close slower into consonants. Also, the longer a vowel is held, generally the more open the mouth. Here is an exercise just for lip sync.
Animating dialogue is not simply making the character appear to be talking but to make the character act. This is something a character animator works on an entire career. Here is my first taste of it. The first video is something I did on the side. The voice is my friend Jarryd Meyer prank calling a blood bank. This was practice for our dialogue assignment.
The assignment was to record one six second line of dialogue, then animate a character delivering the line. The character must be shown in a wide shot (full body) and use his whole body to act. I decided to go for some serious over acting. The line is delivered by Nathan (sorry, don't know his last name) who is a very talented voice actor. This was definitely the hardest assignment of the first semester.
Animation can be set to music as well as sound effects. A beat can be placed at a regular number of frames (for example an accent every 12 frames), then music can be written to match or music with the same beat can be used. Sound effects can be broken down frame by frame and noted on an exposure sheet. Of coarse, syncing to music can be much more complex. Mark Mayerson and Amir Avni both wrote excellent posts on the subject. This is one of my favorite aspects of animation. Below is one of my favorite examples of music and animation synced.
Our final assignment for the semester was to animate a character moving around to music. The actual syncing with the music was not part of the grade. It was more about showing all the principles we had covered during the semester. Since the character had to jump around, I did not try to sync it to the music at all. The jumps take too long to hit every beat. The assignments were linked up to form a class anajam. At the beginning of each assignment we were to morph the previous character into our character.. This was to be synced with a sound effect we recorded.
The first video is my assignment. The next is that of the whole class.