Читать книгу Engineering Acoustics - Malcolm J. Crocker - Страница 169

Figure 4.23 shows a block diagram of an empirical Zwicker‐type dynamic loudness meter (DLM) that includes the spectral and temporal loudness processing portrayed in Figures 4.21 and 4.22 [22]. First, the spectral processing (1 and 2) shown in Figure 4.22 using the critical band filter bank concept, upward spread of masking (7), and spectral summation (8) are illustrated. Second, the temporal processing discussed in relation to Figure 4.23 is observed as shown in the blocks marked envelope extraction, postmasking, and temporal integration (see steps 3, 6, and 9.) Lastly and of most importance is step 5 (labeled loudness transformation), which represents the fact that the loudness is assumed to be proportional to the square root of the sound pressure (or the fourth root of the sound intensity. See Figure 4.21c.).

Figure 4.23 Block diagram of a dynamic loudness meter (DLM) [46].

One advantage of the DLM discussed and shown in Figure 4.23 is that, by suitable modification of the DLM loudness transformation (step 5), the loudness perception of both normal hearing and hearing impaired subjects can be simulated [22]. This fact is important since the aging population in industrialized countries has suffered varying degrees of hearing impairment that should be allowed for in sound quality simulations. Some fraction of the younger population may have suffered mild to moderate hearing loss because of exposure to intense noise during recreational or leisure time activities [22].