# Auditory Perception of Impulsiveness and Tonality in Vocal Fry
## 4 Discussion  
The perception of vocal fry with regular vocal fold oscillations was studied in two listening experiments in the current study. The first experiment considered glottal frequency Fo, open quotient Qo, and glottal area pulse skewness Qs. The perception of vocal fry in synthesized vowels was shown to be mainly affected by the glottal frequency Fo. When Fo is below a listener-individual threshold ranging from 40 to 80 Hz, the phonation is classified as fry. This classification agrees with previously reported observations that associate fry with a low pitch [12; 37]. The open quotient Qo also had an effect on fry perception. A smaller open quotient was a significant cue for fry for a minority of listeners, which agrees with past findings [22]. No measurable effects on perceptual ratings were found for the pulse skewness Qs. This result agrees with previous findings [22] that found Qs to be relevant to the perception of vocal effort rather than vocal fry. The second experiment studied the influence of the short-term context (i.e., within-vowel context) on the perception of vocal fry. Different values were assigned to glottal parameters Fo and Qo before and after the fry mid-vowel segment. We tested whether the amount of variation of Fo and Qo affects listeners' ratings of fry to determine whether listeners are susceptible to perceptual bias due to the short-term context. While the influence of \(\Delta\)Fo on binary fry labeling was marginally non-significant (see Table 1), it had a small but significant effect on the more finely resolved ratings of perceived impulsiveness, tonality, and naturalness (see Table 3). In the context of prior work, we first found that perceived impulsiveness may indeed be understood as a proxy for perceived binary fry, suggesting that graduations between modal voice and fry exist. In particular, perceived binary fry was predicted with a small error by perceived impulsiveness. In addition, the agreement that we found between perceived impulsiveness and LPP is another indicator of the existence of graduations of fry. LPP is inspired by the fluctuation strength model presented previously [26]. In particular, the fluctuation strength refers to the peak prominence of the temporal fluctuation of the masking threshold, whereas LPP refers to the peak prominence of the temporal fluctuation of the loudness. These concepts are similar, but we may argue that fluctuation of loudness is more relevant in our case, because the analyzed signal is not a masker. LPP is also related to the reported threshold of 42-44 dB SPL decay during time intervals between prominent glottal pulses [21]. Second, we showed that tonality (i.e., pitch strength) increases with Fo. This was shown previously for signals with frequencies larger than or equal to 120 Hz [31]. For signals with lower frequencies, a loss of the tonal quality was reported with decreasing Fo [38]. The signal was reported to smoothly transit into a pulsating one when Fo is further decreased, with a transition occurring between 100 Hz and 50 Hz. A value of about 20 Hz was reported to be the lower limit of pitch perception. In addition, reducing the open quotient makes glottal area pulses shorter, which increases the magnitudes of high-frequency harmonics. This causes perceived pitch strength to decrease, possibly via the same mechanism that decreases the pitch strength of complex tones as opposed to pure tones [26]. However, if the open quotient exceeds 0.7, which is typical for breathy phonation, this effect may be reversed, because breathiness was previously shown to be inversely correlated with pitch strength, most likely due to the increased level of aspiration noise [39; 40]. Third, regarding naturalness, the predominant effect was a perceived increase in naturalness with vibration frequency, which suggests that the synthesis of vocal fry with frequencies down to 20 Hz remains a challenge.