One of speech synthesis main problems is synthesis of unvoiced fricatives. One of our previously stated conclusions is that consonant x is influenced by before and behind existing phonetic elements. The aim of experiments described in this paper is to evaluate influence of different x allophones for speech intelligibility and automatic speech recognition.

In this paper the formal system, which describes allophones and, at the same time, phonemes interrelations in their possible sequences in natural language, is described. The formal system is necessary for automatic speech synthesis questions' solution. The experiments of two different types were carried out in order to evaluate the resemblance between two different ω^x allophones: a) ω^x allophones resemblance analysis based on expert evaluation; b) ω^x allophones resemblance analysis based on automatic speech recognition results evaluation.

Experiment's results corroborated that ch allophones differ and depend from the context, i.e., from neighboring vowels, different ch allophones have influence on speech intelligibility, and therefore different ch allophones for high quality speech must be synthesized.