This module uses the CART tree in int_accent_cart_tree to predict
if each syllable is accented or not. A predicted value of NONE
means no accent is generated by the corresponding Int_Targets_Simple
function. Any other predicted value will cause a `hat' accent to be
put on that syllable.
A default int_accent_cart_tree is available in the value
simple_accent_cart_tree in lib/intonation.scm. It simply
predicts accents on the stressed syllables on content words in
poly-syllabic words, and on the only syllable in single syllable content
words. Its form is
(set! simple_accent_cart_tree
'
((R:SylStructure.parent.gpos is content)
((stress is 1)
((Accented))
((position_type is single)
((Accented))
((NONE))))
((NONE))))
The function Int_Targets_Simple uses parameters in the a-list
in variable int_simple_params. There are two interesting
parameters f0_mean which gives the mean F0 for this speaker
(default 110 Hz) and f0_std is the standard deviation of
F0 for this speaker (default 25 Hz). This second value is used
to determine the amount of variation to be put in the generated
targets.
For each Phrase in the given utterance an F0 is generated starting at
f0_code+(f0_std*0.6) and declines f0_std Hz over the
length of the phrase until the last syllable whose end is set to
f0_code-f0_std. An imaginary line called baseline is
drawn from start to the end (minus the final extra fall), For each
syllable that is accented (i.e. has an IntEvent related to it) three
targets are added. One at the start, one in mid vowel, and one at the
end. The start and end are at position baseline Hz (as declined
for that syllable) and the mid vowel is set to baseline+f0_std.
Note this model is not supposed to be complex or comprehensive but it offers a very quick and easy way to generate something other than a fixed line F0. Something similar to this has been for Spanish and Welsh without (too many) people complaining. However it is not designed as a serious intonation module.