Periodicity estimation in synthesized phonation signals using cepstral rahmonic peaks

Aperiodicity in sustained phonation can result from temporal, amplitude and waveshape perturbations, turbulent noise, nonlinear phenomena and non-stationarity of the vocal tract. General measures of the periodicity of the voice signal are of interest in, for example, quantifying voice quality and in the assessment of pathological voice. High and low quefrency cepstral techniques are employed to supply an index of the degree of voice signal periodicity. In the high quefrency region, the first rahmonic is used to provide an indication of the periodicity of the signal. A new measure, SRA (sum of rahmonic amplitudes) – utilising all rahmonics in the cepstrum, is tested against synthesis data (six levels of random jitter, cyclic jitter, shimmer and random noise). In addition, an existing popular technique using the first rahmonic (cepstral peak prominence, CPP) is assessed with synthesis data for the first time. Both measures decrease with increasing aperiodicity levels of the glottal source, decreasing more noticeably for noise and random jitter than for shimmer and cyclic jitter. CPP is shown to be relatively f0-independent; however, the index appears to be less sensitive when compared against SRA.