## 1 Introduction  
Following laryngeal cancer and total laryngectomy, patients lose the ability to communicate using spoken language. People suffering from laryngeal cancer undergo a laryngectomy surgery, which involves removing the larynx (which contains the vocal cords) and separating the respiratory tract from the nasal cavity and mouth. The consequences of total laryngectomy and the organ system in a healthy and a laryngectomised person are shown in Figure 1.  
Total laryngectomy is a life-saving procedure, performed only when the cancer is so advanced that it is impossible to use alternative methods of treatment. However, the postoperative mutilation of the patient is significant and for these people, effective rehabilitation, the aim of which is to develop the ability to use substitute speech, is a priority. There are three methods of speech rehabilitation:  
* tracheoesophageal (TE),
* electrolarynx (EL)
* oesophageal speech (ES)  
TE is a surgical and prosthetic procedure involving the implantation of a speech prosthesis, most often during laryngectomy surgery. It is also possible to implant a voice prosthesis after the completion of oncological treatment. In this surgical procedure, a fistula is placed between the trachea and the oesophagus, allowing patients to produce tracheoesophageal phonation with pulmonary air. This allows, when the tracheostomy opening is closed using a finger, exhaled air from the lungs to be directed to the oesophagus and hypopharynx [1]. EL is a portable, battery-powered device that is pressed against the tissues of the neck to introduce electromechanical energy into the vocal tract [3]. Although EL is easier to use, it has limitations that make it difficult to generate phonetic information such as accent and intonation, and EL speech sounds like machine speech. ES is one of the major methods of speech rehabilitation. It is a learned technique in which air is swallowed (\"injected\") into the and then allowed to escape through the pharynx. Appropriate tensing of the pharyngeal walls during expiratory airflow results in vibration of the pharyngeal walls, which creates sound. Oesophageal speech is typically of lower frequency pitch than normal speech frequencies because of the characteristics of the pharyngeal wall. The advantages of this technique are that it requires no surgical procedure, prosthesis, or cumbersome hand motions [4; 5]. Sentences spoken with ES take longer than physiological speech because the patient has to replenish the swallowed air. ES is one of the most popular voice rehabilitation methods. The sounds obtained through ES are closer to the laryngeal voice compared to speech generated by TE and EL. However, their intelligibility and quality may be worse than in the case of laryngeal speech. It depends on the individual predispositions of the patient. Reduced oesophageal speech quality results from many factors, including low intensity and fundamental frequency (F0) and the presence of noises generated by its production mechanism [6; 7]. The advantages of speech rehabilitation by ES include:  
* Non-surgical method;
* Hands-free talking;
* Closest to physiological speech;
* No need to implement a foreign body. Disadvantages of oesophageal speech:
* Learning takes a lot of time and must be intensive;
* Not all people are able to master this method well;
* Speech may be incomprehensible;
* Speaking in short sentences and at a slower pace--having to swallow air while speaking [8; 9]. Speech signal analysis can be performed by analysing the time domain, spectrum domain, cepstrum domain, and other solutions proposed by researchers. The ability to identify physical features of speech is provided by the MPEG-7 standard [10] description  
Figure 1: Organ system in a healthy and a laryngectomised person. Visible tracheostomy [2]. definition database.