Kerning is
the process of adding or subtracting space between specific letter pairs.
Tracking is
the process of creating an equal amount of spacing across a range
of letters. Positive kerning or tracking values move characters
apart (increasing the spacing from the default); negative values
move characters closer together (reducing the spacing from the default).
Note:
When you open a project that
was last saved in After Effects 6.0, text in the project may lie
differently than in After Effects 6.0 because of improvements in kerning
behavior.
You can automatically kern type using metrics
kerning or optical kerning. Metrics kerning uses kern pairs, which
are included with most fonts. Kern pairs contain information about
the spacing of specific pairs of letters such as LA, To, Tr, Ta, Tu, Te, Ty, Wa, WA, We, Wo, Ya,
and Yo. After Effects uses metrics kerning by default
so that specific pairs are automatically kerned when you import
or type text.
Some
fonts include robust kern-pair specifications. For other fonts,
or for two different typefaces or sizes in a line, you may want
to use the optical kerning option. Optical kerning adjusts the spacing
between adjacent characters based on their shapes. You can also
use manual kerning, which is ideal for adjusting the space between
two letters. Tracking and manual kerning are cumulative, so you can
first adjust individual pairs of letters and then tighten or loosen
a block of text without affecting the relative kerning of the letter
pairs.
Note: Values for kerning and tracking affect Japanese text,
but normally these options are used to adjust the aki (spacing)
between Roman characters.

Tracking set to default value of 0 (left), Tracking set to
-50 (center), and Tracking set to 200 (right)