Envelope expansion of sine wave vocoded speech

Objective: Present study investigated the effect of envelope expansion on sine wave vocoded speech. Speech recognition score for sine wave vocoded stimuli was assessed in quiet as well as in presence of background noise. Materials and Methods: The test stimuli consisted of four lists, each containing ten HINT (Hearing in noise test) sentences spoken by a female speaker, subsequently each of these stimulus sentences were divided into 8 frequency bands and an envelope was extracted from each frequency bands at 400Hz cut off. Envelope was expanded using overlap and add algorithm (OLA) at the modulation frequencies from 1 to 30 Hz. Ten adult individuals participated in the perceptual task. Results: Speech recognition scores in the presence of background noise was significantly poor when compared to speech recognition in quiet test revealed no significant main effect of envelope expansion on speech recognition in quiet as well as in noise. Conclusion: Envelope cues alone are sufficient for good speech recognition in quiet but not in the presence of noise. Envelope expansion scheme does not affect the sentence perception containing only envelope cues in quiet as well as in noise.