Fundamental frequency (F-0) extraction is often used in voice quality analysis'. In pathological voices with a high degree of instability in F-0, it is common for F-0 extraction algorithms to fail. In such cases, the faulty F-0 values might spoil the possibilities for further data analysis. This paper presents the correlogram, a new method of displaying periodicity. The correlogram is based on the waveform-matching techniques often used in F-0 extraction programs, but with no mechanism to select an actual F-0 value. Instead, several candidates for F-0 are shown as dark bands. The result is presented as a 3D plot with time on the x axis, correlation delay inverted to frequency on the y axis, and correlation on the z axis. The z axis is represented in a gray scale as in a spectrogram. Delays corresponding to integer multiples, of the period time will receive high correlation, thus resulting in candidates at F-0, F-0/2, F-0/3, etc. While the correlogram, adds little to F-0 analysis of normal voices, it is useful for analysis of pathological voices since it illustrates the full. complexity of the periodicity in the voice signal. Also, in combination with manual tracing, the correlogram can be used for semimanual F-0 extraction. If so, F-0 extraction can be performed on many voices that cause problems for conventional F-0 extractors. To demonstrate the properties of the method it is applied to synthetic and natural voices, among them six pathological voices, which are characterized by roughness, vocal fry, gratings/scrape, hypofunctional breathiness and voice breaks, or combinations of these.
2003. Vol. 114, no 5, 2934-2945 p.