### 18.2 Simple intonation ¶

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.