In this work is analyzed the use of digital filter to improve the quality of a speech signal. For this purpose the influence of noises on the understanding of language is inspected and the digital filter design with optimal pole placement is presented. In the process of experimentation the speech signal was recorded by using Praat program, generated noise is made by means of Matlab function randn (n) or the sum two or one cosines. The notated speech signal is mixed with the generated noise. The algorithm based on Matlab program is created to sum up the meanings of speech signal with the corresponding meanings of the noise amplitudes. In order to improve the quality of speech signal mixed with the generated noise, the low pass, notch and strip filters is used, depending on noise, which has been used for connection of noise and a speech signal. The used programs are written down by program Matlab. In the end of the work are show the texts of the algorithms, the text of the created filters and groups of words.