Maurycy J. Kin

Subjective and objective evaluation of sound quality of radio programs transmitted via Digital Audio Broadcast (DAB+) System

The work presents results of research on the sound quality of different radio programs transmitted via Digital Audio Broadcasting (DAB+). This assessment has been provided with a use of psychoacoustic model as well as standard listening tests, using an ACR (Absolute Category Rating) method of scaling, and CCR (Comparison Category Rating) method. Results have shown that sound quality gets worse when bit-stream is of the lowest values (48 kbit/s or 24 kbit/s). Application of the Spectral Band Replication processor significantly improves the perceived quality, which is satisfying for bit streams higher than 64 kbit/s, particularly for jazz and popular music. The assessment with ACR method (recommended for broadcast by International Telecommunication Union) showed better notes than CCR one. It means that recommended method is less critical. Also results obtained with psychoacoustic model are more similar to obtained with CCR method. The attributes of spatial impression change in different ways. The greatest distortion has been observed for the perspective and spaciousness of sound image, while the sound color as well as localization stability and accuracy of phantom sources remained almost the same.

Perception of roughness in harmonic multitones

This paper presents results and problems of perception of mixed modulation (MM) in harmonic multitone for higher modulating frequencies (70 and 200 Hz), and a 5‐harmonics complex. Results indicated that perception of frequency modulation at the presence of the threshold values of amplitude modulation is different than the perception of amplitude modulation at the presence of the threshold values of frequency modulation. It means that two mechanisms of perception for these kinds of modulation exist. It turns out that for perception of this kind of modulation, the hearing system uses two sidebands produced by modulation process, but the high sideband seems to be more important than the low one. Another phenomenon is the perceptual grouping mechanism: for some of the modulated partials MM can be perceived as an additional pitch occurring in multitones, which usually is out of tune for fundamental frequency of the complex. The summation of the partials in one critical band takes place, which suggests that a s...