# Auditory Perception of Impulsiveness and Tonality in Vocal Fry
## 2 Materials and Methods
### Listening Experiments  
In total, 13 listeners (age ranging from 24 to 66 years, seven women and six men) participated. Twelve of the listeners (i.e., listeners 1 to 12) participated in Experiment 1, while eight of the listeners (i.e., listeners 3, 6, 7, 9-13) participated in Experiment 2. All were experienced in perceptual rating of voice quality. Five were speech therapists (listeners 1, 2, 6, 8, and 11), five were speech scientists (listeners 3, 7, 9, 10, and 12), and three were medical doctors (listeners 4, 5, and 13). That diversity made it possible to observe  
Figure 2: Glottal area waveforms generated using the PDOS model. The effective glottal area waveform \(\mathrm{a_{g}}\) is obtained by the minimum operator of the glottal entry and exit areas \(\mathrm{a_{entry}}\) and \(\mathrm{a_{exit}}\) (Equation (5)). differences in behavior between individuals of diverse backgrounds; however, a formal comparison between professions was not possible because of the small number of listeners per profession. Most of the listeners are native German speakers, with the exception of two speech scientists who speak Luxembourgish and Telugu. The task was to rate the tonality and impulsiveness of the stimuli and to evaluate the presence or absence of binary fry. To monitor the perceived naturalness of the synthetic sounds, listeners were asked to rate the naturalness of the stimuli. A 7-point Likert scale was displayed on a graphical user interface (GUI) for each of the attributes: tonality, impulsiveness, and naturalness. The scales ranged from \(-3\) (atonal, non-impulsive, artificial) to \(+3\) (tonal, impulsive, natural). Additionally, listeners were asked to provide a yes/no reply regarding the perceived presence of fry. At the beginning of each experiment, eight (\(2^{3}\)) stimuli obtained using all combinations of the most extreme parameter values \(\mathrm{Fo_{M}}\), \(\mathrm{Q_{OM}}\), and \(\mathrm{Q_{M}}\) were presented to anchor and familiarize listeners with the range of voice qualities covered by the evaluation scales and to increase the expected reliability of the ratings [31]. After anchoring, the main corpus was rated. Next, listeners rated stimuli chosen randomly from the main corpus a second time for testing intra-rater reliability. The stimuli within the three blocks (anchoring, main corpus, repetitions) were presented in a random order, which was the same for all listeners. The listeners were allowed to listen to each stimulus as often as they wished. Figure 3 illustrates the effects of model parameters \(\mathrm{Fo_{M}}\), \(\mathrm{Q_{OM}}\), and \(\mathrm{Q_{M}}\) on the glottal area, the glottal flow rate, and the acoustic pressure at the lips. The vibration frequency and the open quotient are controlled directly by corresponding model parameters, that is, \(\mathrm{Fo}=\mathrm{Fo_{M}}\) and \(\mathrm{Q_{O}}=\mathrm{Q_{OM}}\). However, the skewness of glottal area pulses is controlled by the model parameters amplitude quotient and the open quotient: \(\mathrm{Q_{S}}=\mathrm{f(Q_{M},Q_{OM})}\). Thus, for evaluation with regard to skewness, \(\mathrm{Q_{S}}\) is extracted from glottal area waveforms according to Equation (2) obtained via linear regression \(\mathrm{Q_{S}}=-1.26+2.09\cdot\mathrm{Q_{M}}+0.56\cdot\mathrm{Q_{OM}}\) with \(\mathrm{R^{2}}=0.96\). Figure 4 compares examples of acoustic pressure waveforms of the stimuli and illustrates changes in glottal parameters for the two experiments. Both experiments were carried out on a personal computer. The pre-rendered stimuli were played back via a Lexicon Omega external sound card and AKG K271 headphones. Figure 3: The impact of the control parameters \(\mathrm{Fo_{M}}\), \(\mathrm{Q_{OM}}\), and \(\mathrm{Q_{M}}\) (**a–c**) of the PDOS model on the glottal area waveform (black solid line), glottal flow rate (gray dash-dotted line), and acoustic pressure (gray solid line). As expected, the glottal flow rate is skewed to the right with regard to the pulses seen in the glottal area.