## 4 Discussion  
The human voice is a product of the aerodynamic energy (i.e., subglottic pressure provided by the lungs) conversion into acoustic energy [39]. The transglottal airflow pulse is determined by how long vocal folds remain closed, which is associated with the intensity and definition of harmonics produced in the glottal source [40]. Hence, incomplete glottal closure provides turbulent airflow, which reduces the acoustic signal harmonic structure and increases the amplitude variability [4, 41], which results in the audible vocal quality disturbances classified as breathiness [42]. Furthermore, differences in muscle tone and mass in vocal folds cause the variability of frequency and amplitude in the acoustic signal and result in an audible vocal quality disturbance classified as roughness [4]. Roughness is described as an unpleasant low-pitched noise [42]. At last, strain and general degree indicate the auditory perception of vocal effort and global characteristics of the voice, respectively [43]. Regarding auditory-perceptual analysis, since the VAS scores were below 35.5 points, the VHG scores indicate a normal variation of voice quality [44]. DG had a mild to moderate vocal quality deviation (35.6 to 50.5 points). So, the complementary analysis evidenced that VHG had statistically inferior values than DG. Since auditory-perceptual analysis may be inconsistent and biased due to its subjectivity [19], acoustic measures (i.e., robust and objective method for voice analysis) must be associated with the auditory-perceptual analysis to assist the understanding of phonation system mechanisms. Besides, CPPs and LTAS measures use robust algorithms, are more accurate, allow a complete analysis, are not invasive, are low cost as well as more used in studies to assess the vocal quality [16, 23, 24, 25, 26, 42, 45, 46, 47]. Thus, this study contributes to evidence by associating robust measures with auditory-perceptual analysis. CPPs amplitude provides information on the dominant rahmonic periodicity, which corresponds to F\({}_{0}\)[9]. The harmonics are multiples of F\({}_{0}\) and are produced at glottal source in a one-second period (i.e., the occurrence moment of cepstral peak), called quefrency, which determines the period of a glottal cycle [15] and can be expressed by:  
\[T=\frac{1}{F_{0}}\]  
where \(T\) is the period. In this case, it corresponds to quefrency (s), and \(F_{0}\) is the fundamental frequency value (Hz). We highlight that rahmonic and quefrency are anagrams to harmonic and frequency, respectively. When CPPs have increased amplitude, there is a better harmonic definition, which is a characteristic of vocal fold cycle regularity [11]. We could observe that in our study as, for vowel /a/ emission, there were negative correlations with breathiness and general degree in both groups and with strain in DG. Regarding continuous speech, there were negative correlations with general degree and roughness in VHG. In other words, we believe that voices with an increased deviation of general degree, roughness, and breathiness have a less regular acoustic signal produced in the glottal source, thus decreased CPPs. Furthermore, excessive contraction of intrinsic and extrinsic laryngeal muscles that result in the auditory-perceptual parameter of strain [42], present with a higher deviation in dysphonics, can also reduce the acoustic signal periodicity. The alpha ratio provides information on the spectral slope [27], and there was a negative correlation with breathiness for continuous speech in VHG. We observed that when there are increased alpha ratio values (less negative values), the deviation degree of breathiness decreases. A possible explanation is when the vocal tract (filter) is inertive and the flow declination rate is faster than the glottis area declination rate, the voice is brighter and more projected, leading to a less steep spectral slope (i.e., more energy in harmonics above 1 kHz) [33, 48, 49]. It is important to highlight that the glottis must be normotensive and close properly.