Speech signal

Speech signal

Speech signal is the basic study and analysis material in speech technology
as well phonetics. To form meaningful chunks of language, the speech signal
should have dynamically varying spectral characteristics, sometimes varying within
a stretch of a few milliseconds. Phonetics groups these temporally varying spectral
chunks into abstract classes roughly called as allophones. Distribution of these allophones
into higher level classes called phonemes takes us closer to their function in a
language. Phonemes and letters in the scripts of literate languages – languages which
use writing have varying degrees of correspondence. As such a relationship exists,
a major part of speech technology deals with the correlation of script letters with
chunks of time-varying spectral stretches in that language. Indian languages are said
to have a more direct correlation between their sounds and letters. Such similarity
gives a false impression of similarity of text-to-sound rule sets across these languages.
A given letter which has parallels across various languages may have different
degrees of divergence in its phonetic realization in these languages. We illustrate
such differences and point out the problem areas where speech scientists need to pay
greater attention in building their systems, especially multilingual systems for Indian
languages.