Subject: Speech Processing

Topic: Speech Processing Applications

Difficulty: Low

(i) The ASR problem can be considered as a mapping from a speech signal to a sequence of phonemes, words and sentence.

(ii) The major obstacle to high accuracy recognition is the large variability in the speech signal characteristics.

(iii) The variability is categorized as linguistics variability, speaker variability and channel variability.

(iv) Linguistic variability includes the effects of phonetics, phonology, syntax, semantics and discourse on the speech signals.

(v) Speaker variability includes intra and inter speaker variability. It also includes the effects of co-articulation, that is, the effects of neighboring sounds on the acoustics realization of a particular phoneme.

(vi) Channel variability includes the effects of background noise and the transmission channel noise.

(vii) Variability will generate uncertainty in the recognition which must be taken care of by the recognition process.

(viii) The improvement in speech recognition performance have reduced the word error rates in ARPA program by a factor of 5 in 5 years.