Temporal and Spectral Processing Methods for Processing of Degraded Speech: A Review <s> Cepstral Processing <s> A common type of interference in speech transmission is that caused by the speech of a competing talker. Although the brain is adept at clarifying such speech, it relies heavily on binaural data. When voices interfere over a single channel, separation is much more difficult and intelligibility suffers. Clarifying such speech is a complex and varied problem whose nature changes with the moment‐to‐moment variation in the types of sound which interfere. This paper describes an attack on the principal subproblem, the separation of vocalic speech. Separation is done by selecting the harmonics of the desired voice in the Fourier transform of the input. In implementing this process, techniques have been developed for resolving overlapping spectrum components, for determining pitches of both talkers, and for assuring consistent separation. These techniques are described, their performance on test utterances is summarized, and the possibility of using this process as a basis for the solution of the general two‐tal... <s> BIB001 </s> Temporal and Spectral Processing Methods for Processing of Degraded Speech: A Review <s> Cepstral Processing <s> Two signal‐processing algorithms, derived from those described by Stubbs and Summerfield [R. J. Stubbs and Q. Summerfield, J. Acoust. Soc. Am. 84, 1236–1249 (1988)], were used to separate the voiced speech of two talkers speaking simultaneously, at similar intensities, in a single channel. Both algorithms use fundamental frequency (F0) as the basis for segregation. One attenuates the interfering voice by filtering the cepstrum of the signal. The other is a hybrid algorithm that combines cepstral filtering with the technique of harmonic selection [T. W. Parsons, J. Acoust. Soc. Am. 60, 911–918 (1976)]. The algorithms were evaluated and compared in perceptual experiments involving listeners with normal hearing and listeners with cochlear hearing impairments. In experiment 1 the processing was used to separate voiced sentences spoken on a monotone. Both algorithms gave significant increases in intelligibility to both groups of listeners. The improvements were equivalent to an increase of 3–4 dB in the effect... <s> BIB002
Stubbs and Summerfield BIB002 compared the harmonic selection procedure suggested by Parsons BIB001 , with the cepstral transformation of speech. The cepstral transformation maps the spectral envelope to a region near the origin of the cepstral domain, and maps the harmonic excitation to a position well separated from the origin. For voiced speech, the harmonic excitation was simply an impulse with cepstrum quefrency equal to the pitch period. If the pitch peak in the cepstrum was attenuated, the harmonic excitation was reduced. The success of this filtering operation usually requires one voice to be stronger than the interfering voice. Therefore, speech separation not only depends on the processing method used but also on the nature of the degraded signal. The more separated the pitch and harmonics of each talker, the better the results to be expected.