Precision muscles are a set of core muscles that work in combination to achieve precise, systematic behaviors, including speech and blinking.
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Speech involves coordination between multiple fast-moving articulators (tongue, teeth, lips, jaw) to form closures and constrictions at exact times. For example, to make a /p/ sound, the lips and jaw must coordinate so the lips meet firmly with no gap or interpenetration.
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Blinking requires the eyelids to meet precisely without undershoot or overshoot. In the presence of other eye changes like squinting or squeezing, there must be coordination between the blink muscle and these other muscles.
The 21 precision muscles are as follows.
Eyelids
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blink
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eye_close
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eye_flare_L
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eye_flare_R
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eye_squeeze_L
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eye_squeeze_R
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eye_squint_L
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eye_squint_R
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lower_eyelid_flex_L
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lower_eyelid_flex_R
Lips
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adduction
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compression
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lip_flare
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lip_seal
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lower_lip_pull
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lower_lip_push
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pinching
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retraction
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rounding
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upper_lip_pull
Jaw
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jaw_opening
Collectively, the poses driven by the precision muscles are called the base poses. Due to the extra precision requirements, base poses more numerous and contextualized than standard muscle poses, and have stricter standards.
Precision muscles and base poses cannot be deleted.
Relationship of precision muscles to base poses
A base pose can be triggered on some sub-range of a muscle’s activation. For example, each of these two base poses
is activated at different levels of the muscle jaw_opening.
Base poses can also be driven based on multiple muscle activations. For example, the activation of each of these base poses
is dependent on the combined activation of adduction and jaw_opening muscles.
Setup of base poses
It is not necessary to understand what muscles drive which base poses or how they are connected, but it is necessary to adhere to the strict standards for the base poses that are published in the following sections, in order to have accurate lip sync and blinking behavior.
In SGX Studio Maya, the base poses are set up through a guided process. See Editing Muscles for a user guide to the muscles editor in SGX Studio Maya. The setup interface guides the user to set up certain poses before others and uses existing poses to help provide context.
For optimal outcomes, base poses can be set up by the team of specially trained experts at Speech Graphics. It can be helpful to have at least one character set up by us as a starting point. See Setup Services.
When setting up a base pose, you will notice that the starting point is not always the neutral pose. A non-neutral starting pose, called the frame pose, provides the context in which the pose actually occurs, helps expose the right anatomy and enforces points of contact.
For example,
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adduction__ is framed with the jaw 40% open
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tongue_advance__bite_tongue is framed with the jaw slightly open to allow the biting of the tongue, and the lower lip and upper lip retracted to expose the teeth and tongue
Note that the user is not responsible for managing frame poses; this is handled by SGX Studio. Also note that the frame pose is not used in animation; only the delta from frame pose to base pose gets used.