So far the module Int_Target uses a target-interpolation scheme [4] to compute the appropriate F0 curve. Other methods are under investigation.
The file festival/lib/german/ims_german_tobi_rules.scm provides the functions necessary for the prediction of relative F0 values given a sequence of ToBI labels.
To set up this module you can call the function setup_tobi_f0_method. However, since all current voices use this method and the setup is not required for these voices.
In the voice definitions 'Int_Method is sets to 'ToBI and 'Int_Target_Method to 'Int_Targets_General. The latter determines the function used for the prediction of targets within the module Int_Targets. In this case, this function is tobi_f0_targets. It is specified in int_general_params.
For each syllable in an utterance bearing a tone or an accent feature, tobi_f0_targets first predicts targets using one CARTs for pitch accents and end tones each (german_accent_tree and german_endtone_tree). A target is a set of triples consisting of (i) a label indicating the syllable the target belongs to (P for previous, A for actual and N for next syllable), (ii) a value for the relative position of the target within the voiced part of this syllable (given in percent of the voiced part), and (iii) a value for the relative position of the target with respect to the baseline at that particular time (given in percent of the pitch range). In a second step, absolute F0 values are calculated from these relative targets. The F0 contour is finally constructed by an interpolation of the target values.
The file ims_german_tobi_rules.scm also contains some feature functions used in the CARTs for ToBI label prediction within the module Intonation.