Abstract
Human speech becomes impaired i.e., unintelligible due to a variety of reasons that can be either neurological or anatomical. The objective of the research was to improve the intelligibility and audibility of the impaired speech that resulted from a disabled human speech mechanism with impairment in the acoustic system-the supra-laryngeal vocal tract. For this purpose three methods are presented in this paper. Method 1 was to develop an inverse model of the speech degradation using the Cepstral technique. Method 2 was to replace the degraded vocal tract response by a normal vocal tract response using the Cepstral technique. Method 3 was to replace the degraded vocal tract response by a normal vocal tract response using the Linear Prediction technique.
Highlights
Speech impairments or disorders refer to difficulties in producing speech sounds with voice quality [1]
The air from the lungs is forced through the glottis and the tension of the vocal cords is adjusted so that they vibrate at a frequency, known as pitch frequency, which depends on the shape and size of the vocal cords, resulting in a quasi-periodic train of air pulses that excites the resonances of the rest of the vocal tract
The first M samples where M is the number of channels allotted to specifying spectral envelope information [9], typically first 2.5 ms to 5 ms duration, of the cepstrum of a speech segment represent the vocal tract response while the remaining samples represent the glottal excitation signal
Summary
Though non-stationary the speech signal can be considered as stationary over short periods typically 10-50 msec [3,4,5]. Effective bandwidth of speech is 4-7 kHz [4,5]. The elementary linguistic unit of speech is called a phoneme and its acoustic realization is called a phone [7]. A phoneme is classified as either a vowel or a consonant [3,4,5]. The duration of a vowel does not change much and is 70 ms on an average while that of a consonant varies from 5 to 130 ms [3]
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