# Spatial Information on Voice Generation from a Multi-Channel Electroglottograph
## 4 Comparison between Software and Experiments  
The new developed software has been tested by studying the larynx displacement during two well-known vocal acts: the alternate emission of the vowel/**a**, first with a low note and then with a high note; and swallowing.  
In order to guarantee a correct synchronization between the physical (measured) signal and the acquisition (samples acquired), the acquisition chain in Labview should be set to read data in Finite Mode. The sampling rate that allows the best synchronization was estimated to be around 38.5 kHz: using this sampling rate, we could acquire 36 samples every 3.5 ms. It is also important to remember that the EGG signals are normally studied during the emission of a low note characterized by a fundamental frequency of \(f_{0}\approx 100\) Hz. It is also important to note that during the alternate emission of a low and high note, the larynx has a marked displacement, in the range between 18 and 22 mm [14].  
Moreover, the high level of background noise caused some difficulties of accuracy during the acquisition of the experimental data, since the EGG signal has a magnitude of around 1 mV, which is comparable with the background noise. However, this background noise, which represents the main issue during these experiments with an EGG device, is often discussed in scientific literature [14,15].  
Figure 6: Application of MC-EGG on humans.  
In order to reduce the background noise, the first attempt consisted of using a proper contact gel which could increase the ECC signal, improving the contact between the electrode and the skin surface. The second attempt consisted of using a higher voltage range, which was in the order of tens of mV.  
The two codes were initially tested using the Labview code, and then the Matlab code. As expected, Labview allowed us to visualize the larynx in a downward position during the emission of the low note and an upward displacement during the emission of the same note at a higher frequency. There is no back-forward displacement of the larynx during this phonetic act. The range of displacement was 0 mm on the sagittal plane and 18.2 mm on the vertical plane, as described in scientific literature [15].  
The data acquired by the Labview code was processed with the Matlab algorithm. In this way, the larynx movement was graphically visualized. The resulting movement was similar to the Labview one, and the resulting displacement was 0 mm for the sagittal plane and 18.4 mm for the vertical one. Besides the graphs, a video of the displacement was also obtained. Figure 7 reports some frames of the video.  
During swallowing, the path of the larynx inside the neck is more complex; the larynx responds to this act by rising up in the first moment to push down the bolus, the epiglottis then moves backward to avoid the bolus penetration into the respiratory airways and, when the bolus is passed, the larynx returns to the original position.  
The results obtained from the evaluation made through Labview and Matlab confirmed this path [13]. We recorded a 19.7 mm vertical displacement (both in Labview and Matlab), while the sagittal movement was 16.65 mm with Labview and 16.75 mm in Matlab. All these values are inside the range described by scientific literature [15]. Figure 8 reports the swallowing displacement as elaborated by Matlab.  
Figure 7: Frames from the created Matlab movie for the larynx movement.