27 Jan 2004
ToBI or not ToBI: phonetic transcription and the categories of intonation
The ToBI transcription system was intended as a tool for labelling prosodic features of speech databases in standard English. The "tonal" (To) notation in ToBI is based on Pierrehumbert's analysis of English intonation and claims to express PHONOLOGICAL categories, whereas the source of the "break index" (BI) notation was a preliminary IMPRESSIONISTIC PHONETIC transcription comparable to the IPA alphabet. The finished ToBI system modifies the original break index notation to give it a phonological role for which it was not intended; yet at the same time, the tonal notation makes concessions to users who want to transcribe certain impressionistically observable "sub-phonemic" details of alignment and pitch level. Overall, therefore, the theoretical underpinnings of the system are at best somewhat confused.
This inadequate theoretical foundation is increasingly a matter for concern, as ToBI-like systems are being designed for many languages besides English. Designers of such systems generally say that they are basing their notation systems on the "principles" underlying the original ToBI and adapting them to the intonational systems of each new language, but since these principles are not very coherent, in practice the family of ToBI transcriptions is becoming more and more similar to the IPA alphabet. This is particularly true of the "star" notation, which has largely lost its original phonological function and has taken on an implicit phonetic interpretation related to F0/segment alignment.
The use of the star notation for phonetic alignment bears a striking resemblance to the way IPA notational devices represent differences of voice onset time. I argue that in fact ToBI has developed empirical inadequacies that are strongly analogous to the known empirical inadequacies of the IPA alphabet. Since we understand the strengths and weaknesses of IPA transcription fairly clearly, we should refrain from taking ToBI further in the direction of impressionistic phonetic transcription without a clearer acknowledgement of what we are doing and why.