Is it a duplication that AA0 and AA both in the cmudict.symbols file?

[JohnHerry]

Thanks for the job. English is not my mother tongue, but I am learning to do English text-to-speech training. I want the cmudict.syllable as a symbol table to encode English phonemes. as I know the digits at the end of cmudict symbols are stress labels. AA0 means no stress. So do I need the symbol AA and AA0 at the same time in the process of English phoneme coding?

[Alexir]

A good question.
Whether you use AA0 depends on how your synthesizer deals with stress. For example, an unstressed vowel might be shortened or centralized (moved towards AX in phonetic space).

Note that not all entries have this annotation. This dict was developed for speech recognition: At some point, stress marks became less important. Stress was modeled implicitly in triphones, specifically the stressed and unstressed variants of a vowel were represented by (essentially) a bimodal distribution. More recently (and with more training data) they became even less important.