## 1 Introduction  
The vocal folds are located in the larynx and produce the source signal for voice and speech. They start vibrating when the tracheal airflow, coming from the lungs, sets them in motion. During vibration of the vocal folds this airflow is interrupted, resulting in audible sound. After passing the vocal folds, the airflow is further modulated by tongue and lips, producing voice and speech in the process [1,2]. The vocal folds vibrate in varying frequency. Upper range of females' fundamental frequency (F0) were reported to range from 250 Hz [3,4] to 1000 Hz [5]. During singing even higher frequencies of up to 1568 Hz were reported [6]. Vocal fold vibratory patterns can be investigated using several imaging techniques. Videoendoscopy (VS) produces an illusory slow motion by relying on the assumption of the periodic nature of vocal fold vibration. With short strobe light flashes, single images from consecutive oscillation cycles are recorded with a small delay to the previous cycle. These images are then assembled to artificial glottal cycles. However, since VS presents only an artificial slow motion, even subtle variation in periodicity of the vocal fold vibration can result in completely distorted or unrealistic image sequences [7]. Another technique in use is videokymography (VK), which, in contrast to VS, records the vocal fold oscillation at frame rates of about 7000 to 8000 Hz [7; 8; 9; 10], which is distinctly higher than the vocal folds vibration frequency, but can only scan a single line across the glottis [7]. With high-speed videoendoscopy (HSV), the whole glottis is recorded using a high-speed camera [7; 11] with frame rates of currently about 4000 Hz in clinical applications [12; 13; 14; 15]. Hence, HSV overcomes the limitations of VS and VK and combines the advantages of both techniques [7; 11]. Since the introduction of HSV to laryngeal examination, numbers of different studies using HSV have been published [16; 17; 18; 19; 20; 21]. Also, HSV is no longer reserved for scientific use only; the clinical applicability of HSV was tested recently on a larger scale in comparison with VS Ratings of all vibratory features which showed changes between VS and HSV and it was concluded that HSV could enable important refinements in diagnosis and management of vocal fold pathology [22]. As HSV is superior to alternative procedures such as VS and VK [7; 14; 23], it possesses the potential to replace VS [11], the longtime \"gold standard\" and widely used technique of laryngeal examination [24; 25; 26]. However, HSV systems are expensive and these high costs are considered as the most prohibitive factor for the widespread clinical implementation of HSV [7]. A typical clinical examination situation, as it is used for HSV using rigid endoscope, is illustrated in Figure 1. The vibration of the vocal folds is recorded from above [27]. From the recorded data, different features can be extracted. The most prominent and significant feature is the glottal area waveform (GAW). The GAW describes the area between the vocal folds, the \"glottal area\", which opens and closes periodically during normal phonation. For each individual video frame, the glottal area is segmented and lined up in a function as shown in Figure 1b,c. The GAW is defined slightly differently in different works [28; 29; 30; 31]. In this work, the GAW is defined as the function of the glottal area in pixels over frames. All parameters used in this work were calculated using this definition of the GAW. Even though HSV, sometimes done in combination with recording of the audio signal [32; 33], is a powerful method for examining the phonation process [7], the objective parameters obtained from  
Figure 1: (**a**) Recording of the vocal fold oscillations via a rigid endoscope being attached to a high-speed camera. (**b**) Superior view of the vocal folds as seen with the endoscope. (**c**) Computed glottal area waveform (GAW): amount of registered pixels in the glottis over time. both can be influenced by different factors [34; 35; 36; 37; 38].