Ali Alpan

Multi-band dysperiodicity analyses of disordered connected speech

The objective is to analyse vocal dysperiodicities in connected speech produced by dysphonic speakers. The analysis involves a variogram-based method that enables tracking instantaneous vocal dysperiodicities. The dysperiodicity trace is summarized by means of the signal-to-dysperiodicity ratio, which has been shown to correlate strongly with the perceived degree of hoarseness of the speaker. Previously, this method has been evaluated on small corpora only. In this article, analyses have been carried out on two corpora comprising over 250 and 700 speakers. This has enabled carrying out multi-frequency band and multi-cue analyses without risking overfitting. The analysis results are compared to the cepstral peak prominence, which is a popular cue that indirectly summarizes vocal dysperiodicities frame-wise. A perceptual rating has been available for the first corpus whereas speakers in the second corpus have been categorized as normal or pathological only. For the first corpus, results show that the correlation with perceptual scores increases statistically significantly for multi-band analysis compared to conventional full-band analysis. Also, combining the cepstral peak prominence with the low-frequency band signal-to-dysperiodicity ratio statistically significantly increases their combined correlation with perceptual scores. The signal-to-dysperiodicity ratios of the two corpora have been separately submitted to principal component analysis. The results show that the first two principal components are interpretable in terms of the degree of dysphonia and the spectral slope, respectively. The clinical relevance of the principal components has been confirmed by linear discriminant analysis.

Assessment of disordered voice via the first rahmonic

A number of studies have shown that the amplitude of the first rahmonic peak (R1) in the cepstrum can be usefully employed to indicate hoarse voice quality. The cepstrum is obtained by taking the inverse Fourier transform of the log-magnitude spectrum. In the present study, a number of spectral pre-processing steps are investigated prior to computing the cepstrum; the pre-processing steps include period-synchronous, period-asynchronous, harmonic-synchronous and harmonic-asynchronous spectral band-limitation analysis. The analysis is applied on both sustained vowels [a] and connected speech signals. The correlation between R1 (the amplitude of the first rahmonic) and perceptual ratings is examined for a corpus comprising 251 speakers. It is observed that the correlation between R1 and perceptual ratings increases when the spectrum is band-limited prior to computing the cepstrum. In addition, comparisons are made with a previously reported cepstral cue, cepstral peak prominence (CPP).