Lip sync is one of the most challenging aspects of 2D animation, especially when it comes to dialogue. You want your characters to speak naturally and convincingly, without looking stiff or robotic. How can you achieve realistic lip sync in 2D animation? Here are some tips and tricks to help you out.
Phonemes are the basic units of sound that make up speech. There are different types of phonemes, such as vowels, consonants, and diphthongs. Each phoneme has a corresponding mouth shape that you can use as a reference for your lip sync. For example, the phoneme /a/ as in "cat" has a wide open mouth, while the phoneme /f/ as in "fish" has a narrow mouth with the lower lip touching the upper teeth. You can find charts of phonemes and mouth shapes online or in books.
Use a mirror. Acting out the scene and dialogue yourself, trying out a variety of lip/jaw/cheek/eye positions will bring more unique and memorable result. Limited animation restricts you significantly but it doesn't have to be lifeless or stiff.
Acting is everything. The following is a production method for animating minutes and hours when working with an exposure sheet Basic lip-sync in 2D can be achieved by 8 or 9 mouth poses. Use any notation eg: ABCDEFGHI. Design mouth shape-keys for side, three-fourth and front. Following are the Mouth Keys A is a closed mouth, B is slightly open C is an in-between B-D pose. D is wide open, E is the shape of "eeee", F is the "ooo " shape G can be " uuu" shape. H is biting lower lip, I is C mouth with the tongue touching the upper palate, These keys would deal with all mouth shapes for most sounds. You may design additional extremes/character-specific mouth shapes as you like. Chart it on X-sheet and insert appropriately.
Before you start animating, you need to study the audio clip that you are going to lip sync. Listen carefully to the words, the intonation, the emotion, and the pauses. You can also use a software like Audacity to see the waveform of the audio and mark the key points where the phonemes change. This will help you plan your timing and spacing of the mouth movements.
The key frames are the main poses of the mouth that show the most important phonemes in the dialogue. You can draw them on a separate layer or on a sheet of paper. You don't need to draw every single phoneme, just the ones that are most visible or expressive. For example, you can skip the phoneme /h/ as in "hat" because it doesn't affect the mouth shape much, but you should include the phoneme /t/ as in "hat" because it creates a sharp closure of the mouth. You can also exaggerate some key frames to emphasize the emotion or the accent of the character.
The in-betweens are the frames that connect the key frames and create the smooth transition of the mouth shapes. You can use a software like Adobe Animate or Toon Boom Harmony to create the in-betweens automatically, or you can draw them by hand. The number of in-betweens depends on the frame rate and the speed of the dialogue. Generally, you want to have more in-betweens for slower and softer speech, and less in-betweens for faster and louder speech. You also want to avoid having too many or too few in-betweens, as they can make the lip sync look too floaty or too choppy.
The final step is to check the sync of your animation with the audio. You can do this by playing back your animation and listening to the dialogue, or by using a software like Magpie Pro or Papagayo to compare the audio and the mouth shapes. You can also ask for feedback from other animators or friends. If you notice any errors or discrepancies, you can adjust the timing, the spacing, or the mouth shapes accordingly. You can also add some secondary animation to the rest of the face, such as the eyes, the eyebrows, or the cheeks, to enhance the expression and the personality of the character.