Time scaling algorithm of speech signal to assist learning of a foreign language

For basic level students of the foreign languages, normal speed speaking is very difficult to understand perfectly, because of lack of training in understanding of oral language. However when the speed of speaking slow down, in most cases understanding increases. This fact suggests that to improve of learning of the foreign language, it is necessary that students can adjust speed of speaking according to their own understanding level. This paper presents a comparison of two time scaling algorithms when they are used to assist learning of foreign language. Both algorithms consist of a pitch detection stage and time scaling stage. The pitch detection of both algorithms is based on autcorrelation method of the speech signals proposed by Rabiner et al. The time scaling in the first method consist in duplicating the pitch periods of voiced segments while keeping unchanged unvoiced ones. The second method is based on the short time Fourier Transform. Experimental results, MOS (Mean Opinion Scoring) are given using Spanish, French, German, Russian, Japanese and Italian which show desirable feature of both time sealing algorithms when they are using to assist the students to learn foreign languages. The performance of both algorithms when the pitch detection stage has some noise is shown too.