## 1 Introduction
One of these factors is the recording frame rate, which was already investigated for acoustic and GAW signals. For acoustic measures, a sampling frequency of at least 26 kHz was suggested to avoid the introduction of errors [34]. For GAW signals it is reported that up to 90% of parameters were affected by the changes in the frame rate [35]. That study suggested that normative parameter values based on the recording frame rate should be determined and a recording frequency of 4000 Hz seemed to be too low to register all details of vocal fold vibratory patterns. Still, the application of recording frame rates of 4000 Hz in clinical studies was judged as justified, since the parameter changes between 4000 Hz and 15,000 Hz were relatively small for glottal dynamic characteristics and glottal perturbation characteristics. For acoustic signals, the stability of perturbation measures was investigated with deviating results [36; 37; 38]. [PERSON] et al. suggested a minimal sequence length in the order of 100 cycles for the calculation of stable perturbation measures in the acoustic signal [36]. [PERSON] et al. found that frequency and amplitude perturbation measures (APM) were not in agreement for three different analysis systems, even for 110 consecutive cycles [37]. Another investigation was done for the electroglottographic (EGG) signal, which describes the electrical impedance between two electrodes placed on the left and right side of the larynx and changes with vocal fold vibration. The influence of different sequence lengths on EGG and audio was investigated and it was found that two of nine perturbation measures for the EGG signal and two of nine perturbation measures for the audio signal (although not the same measures) were affected by changing sequence lengths [38]. However, to the best of the authors' knowledge, no studies exist examining the influence of the analyzed interval length especially for GAW parameters computed from HSV data. In various studies, perturbation parameters are calculated for the GAW, and often the analyzed sequence length varies [39; 40; 41; 42]. Moreover, the sequence lengths are often given in milliseconds [39; 40]; hence the number of cycles ultimately used to calculate the perturbation measures may vary within these studies. To find out if and how this affects the comparability of these studies, the current work investigated the influence of a differing sequence length on 16 different perturbation parameters. Specifically, period, amplitude and energy perturbation parameters were investigated. The aims of this work can be summarized in the following way:  
1. Examine if varying sequence length affects GAW perturbation parameters. 2. Determine if there is a statistical change in parameters by varying sequence length. 3. Investigate the reason for the susceptibility of these parameters to a changing sequence length. These goals are met by a systematic analysis of all 16 examined perturbation measures. A detailed discussion of the statistically significantly changes in parameters due to varying sequence length was given. The suggestion of the use of at least 20 cycles was given for future studies using HSV data.