## 2 Materials and Methods  
The study group consisted of six people who had undergone a total laryngectomy surgery. This group consisted of three men aged 30 to 70 and three women aged 30 to 60. Those patients were undergoing speech rehabilitation related to learning ES. The patients had mastered the art of oesophageal speech at a communicative level. The words used by therapists for speech rehabilitation were selected for the study. The criterion for selecting the tested words depended on the speech therapists. All words were spoken in Polish. The selection of words depends on the characteristics and features of the Polish language and is related to articulation. Five words were selected for the study, which are presented in Table 1.  
The above-studied words are the basis for the rehabilitation of flowing speech, which is adapted to the specifics of the Polish language. Of particular importance is the articulation of the Polish \"cz\" (/t$/) or \"$\" (//), which requires a specific positioning of the lips and tongue. The above is included in the tested words, which are the subject of the research described in this paper. The same is true for the pronunciation of the Polish \"but\" (/butw/), which is included in the test word \"bulka\" (Eng. a bread roll). The tested words were also recorded from healthy people, and the numerical results related to the F0 frequency studied were used as a reference point to assess the differences between oesophageal speech and physiological speech. The words to be analysed were recorded at the Bydgoszcz Laryngectomy Association (Bydgoszcz, Poland). The recordings were taken in a specially prepared room. The OMNITRONIC IM-1000 PRO condenser microphone (Steinigke Showtechnik GmbH, Waldbuttelbrunn, Germany) was used. Details of the microphone are as follows:  
* XLR output
* Frequency range: 60-18,000 Hz
* Directivity pattern: Cardioid
* Impedance: 400 ohms
* Sensitivity: \(-\)70 dB \begin{table}
\begin{tabular}{c c c} \hline \hline  & \multicolumn{2}{c}{**Studied Words**} \\ \hline
**In Polish** & **In English** & **IPA Notations** \\ \hline beczka & a barrel & /bet$ka/ \\ bulka & a bread roll & /buyka/ \\ jajko & an egg & /jaj.ks/ \\ paczka & a package & /pat$ka/ \\ \$nieg & snow & /greg/ \\ \hline \hline \end{tabular}
\end{table} 
Table 1: List of studied words. All speech samples were recorded in WAV format with a sampling rate of 44,100 Hz and 16 bits/sample. The mean durations of the studied words for healthy and laryngectomised people are presented in Table 2.  
The research being carried out is a continuation of the analysis of oesophageal speech. In previous research, a broad analysis of the time domain, frequency domain, and cepstrum was carried out, and the results were presented in paper [12]. In addition, an analysis of ES was carried out using division of the studied words into phonetic segments, and the results of the research were presented in paper [8]. The author's goal is a broad numerical analysis of oesophageal speech, the synthesis of which will lead to the definition of a precise description of the physical features of ES. The generated ES feature vector will be based on the results of the research included in the publications [8,12] and the results of this research. According to the author, the analysis of oesophageal speech is not yet complete and will be continued, with the results published in subsequent papers. The Octave programming environment was used for signal pre-processing such as cutting out silence and removing noise and artifacts. All work related to obtaining information about the F0 frequency was performed using the Praat program v.6.4.13. The pitch information was taken from the available \"Pitch\" menu option of the Praat program. One of the key options is the pitch range setting, which allows the tested frequency range of the analysed word to be set.