Males' vocal folds, laryngeal structures, and respiratory system undergo physiological and anatomical changes throughout their lives, which causes a major change in the acoustic parameters of their voice. The noise-to-harmonic ratio (NHR), Shimmer (dB), Jitter, and fundamental frequency (F0) are the most often used acoustic metrics for evaluating vocal function. Men have a lower fundamental frequency than women, while prepubescent boys have lower and more closely spaced vocal tract resonances than girls. Each acoustic measure has a distinct clinical use, however when diagnosing voice issues, the qualities of the voice that are related to noise are given more weight. Throughout life, vocal structures undergo a variety of modifications that affect the voice’s varied characteristics, including intensity, frequency, and quality. From birth to senescence, these structural alterations take place. According to Brockmann et al.(2011), factors including gender, vowel, intensity, and F0 should be taken into account in order to achieve appropriate voice assessments.

In order to diagnose and treat voice diseases and to further our understanding of physiological voice aging, it is essential to comprehend how acoustic voice parameters change throughout the course of a person’s life. Numerous facets of these factors are examined in the literature, with an emphasis on the aging, stable adult, and developmental stages. The main conclusions of NHR, Jitter, Shimmer (dB), and F0 are summarized here. There are few research studies focussed on the acoustic characteristics of voice in children, adolescents and the older age groups. According to Titze(1994), F0 drastically changes throughout puberty, particularly in boys, since testosterone causes the larynx to develop quickly. F0 drops by around one octave as a result of this expansion. According to Harries et al.(1997), male F0 stabilizes at a frequency range of 85~125 Hz by the end of puberty, which is consistent with the growth in the thickness and length of the vocal folds. Because of consistent laryngeal architecture and neuromuscular regulation, F0 stays comparatively constant throughout maturity (Boone et al., 2005). Due to vocal fold atrophy and decreased flexibility, F0 marginally rises in older guys. According to Sataloff(2017), older guys had an average increase of 10~20 Hz in comparison to their midlife values.

Linville(2004) found that older males had more Jitter, which they attributed to glottal insufficiency, decreased neuromuscular accuracy, and age-related vocal fold bowing. Children’s elevated Shimmer (dB) is a reflection of their underdeveloped glottal closure and vocal fold vibration. Adults often have Shimmer (dB) levels between 0.2 dB and 0.5 dB, which are stable and indicative of effective phonation (Stathopoulos et al., 2011).

Due to alterations in subglottal pressure regulation and decreased glottal efficiency, elderly males exhibit a marked rise in Shimmer (dB) (Ramig & Ringel, 1983). Children’s inadequate glottal closure and less effective phonation led to higher NHR readings (Titze, 1994). This frequently occurs at times of fast development or hormonal shifts. According to Maryn et al.(2009), adults have the lowest NHR values (around 0.1~0.2), which suggests effective glottal vibration and less noise components. Higher levels of aperiodic noise and decreased glottal closure are reflected in older guys’ elevated NHR. According to Linville(2004), there is a substantial correlation between changes in NHR and perceptual indices of voice roughness and hoarseness.

Hence the human voice is a vital tool for communication, and its acoustic properties can provide crucial insights about bodily changes and development. Vocal parameters such as F0, Jitter, Shimmer (dB), and NHR are essential for evaluating the voice’s health and quality. However, a significant amount of research on vocal acoustics has either focused on certain age groups or been limited to clinical populations. There aren’t many thorough studies that examine vocal parameters throughout a broad age range, especially for healthy males.

The current study proposal was approved by the Institutional Ethical Committee, and the ethical clearance number is 1427(A)/2018.

The above Table 1 represents the mean ± SD values of F0, Jitter, Shimmer (dB) and NHR among male participants.

The data show a gradual decrease in F0 as age increases, with a marked drop from 260.31 Hz in the 6~9 years age group to 125.97 Hz in the 61~70 years age group. This finding aligns with previous research, which suggests that F0, or the pitch of the voice, tends to decline with age, particularly after the third decade of life (Titze, 2000). According to research by Ramig and Ringel(1983), aging has an impact on vocal features. Older persons also showed decreased vocal stability and intensity, as seen by higher Jitter and Shimmer (dB).

Jitter, which reflects the variability in the frequency of vocal fold oscillations, exhibits a rise in values between ages 9 to 12 years which is around 2.6, after which it stabilizes from 16 to 50 years. However, there is a decline in Jitter values in the 60~70 years group, dropping to 0.43. This suggests that, over time, the stability of the voice improves, and frequency perturbations become less noticeable. The trend is consistent with findings that Jitter decreases in older adults, possibly due to changes in laryngeal flexibility and vocal fold elasticity (Hillenbrand et al., 1994).

The mean values of evolution of Shimmer (dB), which measures amplitude perturbation, were closer between the ages of 21 and 50, showing a mean value of 0.3; between the ages of 10 and 15 years, the mean values were 0.8; between the ages of 51 and 60, they were 0.6; and between the ages of 61 and 70, they were 0.4. This suggests that, beyond early adolescence, voice amplitude stability tends to stabilize throughout time with little volatility. According to earlier research, when people age and their vocal fold tissues alter in mass and tension, their Shimmer (dB) values tend to decrease (Simberg et al., 2005).

The NHR, which measures the volume of noise in relation to the voice’s harmonic components, fluctuates minimally between age groups, indicating that voice quality is generally constant throughout life. Between the age range of 13 to 15 and 51 to 60, the NHR mean values increased slightly; the mean value is 0.2, while the mean values for the remaining rage groups are nearly identical, at 0.1. This result is in line with studies showing that aging does not substantially change the voice’s harmonic structure, while having an impact on the fundamental frequency and perturbation measures (Brockmann et al., 2011).

Table 2 provides the statistical significance of differences in vocal parameters of F0, Jitter, Shimmer (dB), and NHR across different age groups of male participants. The p-value of 0.00 (p < 0.05) for all the parameters indicates that the differences between the age groups are statistically significant.

The post hoc analysis comparing average F0 across male age groups showed statistically significant differences (p < 0.05). The following age groups showed exceptions: 16~20 and 21~30 (p = 0.469), 16~20 and 41~50 (p = 0.098), 16~20 and 51~60 (p = 0.014), and 61~70 with 16~20 (p = 0.765) and 21~30 (p = 0.671). Furthermore, there was no significant difference (p = 1.000) between 31~40 and 51~60.

The post hoc analysis comparing Jitter across male age groups showed significant differences (p < 0.05). Comparing age groups 9~12 and 12~15 (p = 0.120), 16~20 and 21~30 (p = 0.410), 16~20 and 31~40 (p = 0.149), 31~40 and 21~30 (p = 0.534), and a number of neighbouring pairs, including 31~40 with 51~60 (p = 1.000) and 41~50 with 51~60 (p = 0.571), were among the exceptions.

The majority of pairwise comparisons, especially those across non-adjacent age groups, revealed significant differences (p < 0.05) in the post hoc analysis comparing Shimmer (dB) among male age groups. The following closely related groups, however, did not differ significantly: 9~12 and 6~9 (p = 0.078), 12~15 and 9~12 (p = 0.994), 21~30 and 31~40 (p = 0.508), 41~50 and 31~40 (p = 0.824), 51~60 and 31~40 (p = 1.000), and several more. According to these findings, Shimmer (dB) exhibits similarities between nearby or overlapping age groups but varies dramatically with age, especially when comparing far age ranges for comparison.

With the exception of significant differences between the 12~15 and younger groups (6~9, p = 0.010; 9~12, p = 0.012) and a few other pairs, such as 16~20 vs. 12~15 (p = 0.043) and 21~30 vs. 12~15 (p = 0.018), the post hoc analysis of NHR across male age groups showed primarily non-significant differences (p > 0.05).

The analysis of voice parameters across different age groups in male participants reveals significant insights into how various aspects of the voice evolve with age.

A steady decline in F0 was observed as age increases, with a substantial drop from 260.31 Hz in the 6~9 years age group to 125.97 Hz in the 60~70 years age group. This aligns with previous studies (Titze, 2000) that show F0 decreases with age, likely due to structural changes in the vocal cords and laryngeal muscles. Jitter values show an increase between ages 10~12 years, stabilizing from 16 to 50 years. In older age groups (61~70 years), Jitter values decrease, indicating improved voice stability. Adolescent voice change in males is a gradual, extended process that occurs over several years (Hollien et al., 1994). These findings corroborate research by Hillenbrand et al.(1994) and Kreiman & Gerratt(2000), which highlight a reduction in Jitter in older adults, likely due to changes in laryngeal flexibility and vocal fold elasticity.

Shimmer (dB) values remain close at most age groups, with a slight fluctuation in the 10~12 years and 13 to 15 years age range (mean value: 0.8) compare to other age groups. This stability in amplitude perturbation is consistent with findings from Simberg et al.(2005), who noted a reduction in Shimmer (dB) with age as vocal fold tissues undergo changes in mass and tension. NHR showed minimal variation across the age groups, indicating that the harmonic structure of the voice remains stable throughout life. This finding aligns with Brockmann et al.(2011) research, which suggests that although age affects pitch and perturbation measures, the harmonic structure of the voice remains relatively unchanged (Boone et al., 2005).

The results conclude that there is a discernible trend toward decreasing pitch (F0) and increasing frequency (Jjitter) and amplitude (Shimmer [dB]) stability as people age. Although there are age-related changes in these characteristics, the voice's harmonic content (NHR) stays constant. The post hoc test results implied that the most of the middle and older age groups have no statistically significant differences between the age groups in F0, Jitter, Shimmer (dB) and NHR. According to these results, age has an impact on the voice’s dynamic and structural characteristics, like pitch and unpredictability, but it has no discernible effect on the voice’s overall harmonic quality.