Oscillations, Waves, and Interactions - GWDG

noise component [GNE]
5
4
3
2
1
cancer groups
normal (n=93)
Speech research 27
whispering (aphon) (n=60)
pseudo-gl. phon. (n=9) aryepigl. phon. (n=6)
glottic phon. (n=15)
ventr. phon. (n=10)
0 1 2 3 4 5 6 7 8 9 10
irregularity component [jitter, shimmer, period correlation]
Figure 1. Göttinger Hoarseness Diagram; distribution of some cancer groups; cf. Ref. [13].
as jitter (period-length fluctuation) and shimmer (amplitude or energy fluctuation);
on the other hand, measures of the noise component relative to glottal excitation.
These are coarse correlates of subjective roughness and breathiness, respectively.
There are many different definitions of such measures; e. g., for irregularity [15]:
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xn − xn−1
xn
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� or
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xn − (1/M) � (M−1)/2
m=−(M−1)/2 xn+m
(1/M) � (M−1)/2
m=−(M−1)/2 xn+m
�
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� , M = 3, 5, . . . ,
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each averaged over n, where xn is the length or amplitude or energy of the nth period.
The period energy is more robustly measurable than the amplitude. For the period
length, a method proved to be especially reliable which was based on the correlation
coefficient of subsequent signal intervals [t, t + T ) and [t + T, t + 2T ) and maximizing
with respect to T [16,17] (with interpolation between the signal samples). The average
correlation coefficient of subsequent periods served as another irregularity measure
(Mean Waveform matching Coefficient, MWC).
Traditional measures of the noise component (e. g., NNE [18], CHNR [19]) are
unfortunately dependent on the irregularity measures and the choice of the analysis
window. With strongly irregular voices, they are often not applicable, since they usually
require a harmonic spectral structure. Therefore, we started from the following
assumption [20]: with glottal excitation – regardless how irregular – the excitation in
different bands should be nearly synchronous, with noise excitation, however, asynchronous.
Hereon the following construction is based. After downsampling to 10
kHz and linear-predictive inverse filtering for removing the formant structure, the
signal is decomposed into partial bands using Hann-window shaped filters. For each
band, the Hilbert envelope is formed and its mean removed. For all pairs of bands