# Influence of the Sound Source's Position on the Stage on the Speech Perception in the Auditorium
## 2 Methods and Materials
### Research Method  
Speech quality assessment was performed using the subjective Absolute Category Rating method, which is recommended by the International Telecommunication Union (ITU) [30] for assessing speech signal quality. This method uses test lists composed of simple, short, semantically unrelated sentences. The list is divided into groups of five short (2-3 s) sentences [38]. In the ACR method, a reference signal is not presented. The listener, after listening to a set of test sentences, gives a speech quality rating on a five-point rating scale in relation to his or her own pattern created in the brain. The MOS (Mean Opinion Score) rating scale reflects the listener's impressions from the best quality, which corresponds to a value of 5, to the worst quality, corresponding to a value of 1 (Table 1). The sentences read by the speaker were recorded under studio conditions. During the research described in this article, the recordings were played back using Audacity 3.5 (22.04.2024) software and NTI Audio TalkBox artificial mouths. The recordings at the study site were made using Reaper v7.15 (17.04.2024) software via an external sound card realised as part of the Roland Studio-Capture audio interface for recordings through Earthworks M23 measurement microphones and an additional CEntrance MixderFace R4 audio interface for recordings using a Neumann KU 100 Dummy Head artificial head. The parameters of the digital recording were a sampling frequency of 48 kHz, and a resolution of 24 bits. The list of equipment used for the recordings is presented in Table 2[39]. A schematic of the measurement/recording system is shown in Figure 1.  
Sentences were spoken fluently, clearly, and in an even voice. Both female and male voices were included in the measurements. ITU-T Recommendation P.800 [30] states that the results obtained for female and male voices should be evaluated separately, and can only be averaged if the difference between them is statistically insignificant. The listening team was selected from among normal listeners according to ITU-T Recommendation P.800 [30]. The listening team consisted of 12 listeners ranging in age from 20 to 25 years. Before the measurements started, the listeners were introduced to the measurement procedure, including how to rate the sentence lists they heard. Listeners gave their ratings after hearing a group of sentences separately for the male and female voices. Each group contained five sentences. The duration of one sentence group was \begin{table}
\begin{tabular}{c c} \hline
**Speech Quality** & **MOS** \\ \hline Excellent & 5 \\ Good & 4 \\ Fair & 3 \\ Poor & 2 \\ Bad & 1 \\ \hline \end{tabular}
\end{table} 
Table 1: Speech quality scale MOS (Mean Opinion Score). Figure 1: Diagram of the measurement/recording system. approximately 10 s. Each group of sentences was followed by an 8 s silence, during which listeners rated the sentences on a five-point scale. After listening to all five groups from the sentence list, the listener's ratings for a given measurement condition (sound source position, type of decoration) were averaged. This resulted in the listener's average MOS value at a given measurement point for each measurement condition. The measurements were performed in situ and in the laboratory. In the in situ measurements, each listener from the 12-person group occupied one of 12 (R01-R12) listening positions in the audience (Figure 2). After listening to all of the sentence lists and giving ratings for three speaker positions on the stage and two types of decoration, the listeners changed their position in the audience. The change of places was continued until each listener had made a rating at all measurement points in the audience. After averaging across listeners, for each measurement point and each sound source location, the rating was given as a Mean Opinion Score (MOS) (Table 1).