Improvements in calculating the loudness of time varying sounds

Recently, a new ISO standard for loudness of arbitrary sounds ISO 532-1 (1) was proposed for the revision of ISO 532:1975 section 2 (method B) (2). It is based on DIN 45631/A1:2010 (3), which includes the widely used standard DIN 45631:1991 (4) for stationary sounds as a special case. ISO 532-1 eliminates uncertainties of existing standards by strictly defining the complete procedure of loudness calculation starting with the waveform of the time signal and ending with specific and total loudness vs. time functions. The strict definition of the complete procedure is a step forward to comparability of calculated loudness results, and fully conforms to DIN 45631/A1:2010 for the sake of continuity. However, although the results of this algorithm are in accordance with the results of many listening tests, there are still phenomena that are not covered by this method. For example, the calculated loudness of sweep signals shows fluctuations, whereas the perceived loudness does not. This is due to the implemented filter bank based on fixed, contiguous third-octave filters. As a possible solution a loudness calculation method is presented that is based on a hearing model (Sottek) using an aurally adequate filter bank of highly-overlapping asymmetric filters (5). In addition, the nonlinearity between specific loudness and sound pressure has been reconsidered in this model according to results of many listening tests (6).