Subjective Assessment of the Intelligibility of Noised Speech in Lecture Room

Abstract

Subjective assessment of the speech intelligibility is of great practical interest, since this parameter can be used in many engineering and natural-mathematical fields, such as bioengineering, design of lecture rooms and concert halls, mathematical modeling and medicine. By this time, several attempts were made to assess the intelligibility of the room. The results of such experiments became conclusions: 1) early reflections improve the intelligibility of distorted noise and reverb speech; 2) using binaural type of listening we will have better intelligibility than with monoural. But to re-implement such experiments, it is necessary to use a lot of expensive equipment, which is not always possible. Therefore, the purpose of this work is to study the influence of the characteristics of the room on the speech  intelligibility without the use of a large number of equipment. The idea of the experiment is as follows: distorted by noise and reverb signals must be listened to by the participants in the experiment, the perceived sound is fixed and compared with the undistorted signal. The clear signal was recorded using a microphone, sound card and audio file software. Synthesis of distorted signals took place in two stages: 1) adding white noise; 2) filtering the resulting mix through a non-recursive digital filter using the impulse characteristics of the room for six distances to the source of sound. The mathematical model of the distorted (output) signal was the convolution of an additive mix of clear signal and white noise with a pulse characteristic. To ensure the necessary signal-to-noise ratio, the noise was weighed by the corresponding coefficients at the stage of adding it to the clear signal. Testing was carried out in five stages: 1) simulating of distorted signals; 2) voicing signal to participant; 3) signal listening; 4) fixation of the perceived sound; 5) intelligibility calculating. For testing, six binaural impulse characteristics of the room with known parameters from the Aachen database of impulse characteristics were used. Each of the impulse characteristics corresponds to a certain value of the distance from the sound source to the microphone. After the completion of the experiment, the overall result was obtained by averaging by the number of participants. The overall result has shown that for small values of the signal-to-noise ratio over long distances, the intelligibility is greater than for small distances. For high values, the signal-to-noise ratio is better for small distances. Such results may be explained by the fact that, at long distances, the combination of the effects of early reflections and binaural listening positively affects the intelligibility. The main reason for the low intelligibility of the distorted by noise speech in the room is a late reverberation. As a conclusion we can say that the computer modeling method makes it easy to create a distorted by the noise and influence of the room signal; It is shown that, for small values, the signal-to-noise ratio is more readable than for small distances.

Keywords

References

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Copyright (c) 2019 Олексій Олегович Андрійченко, Олександр Ігорович Денисенко (Автор)