Abstract:
The current international standard of the equal-loudness level contours specified in ISO 226 is found to involve large errors, epecially for frequencies below 1 kHz. In the past 10 years, a series of experiments has been conducted for full revision of ISO 226 in ISO/TC 43. At the final stage of this project, the new equal-loudness level contours should be drawn from available data points. To do this, the use of an appropriate model for loudness perception is actually useful. A loudness function is proposed by combining that proposed by Lochner and Burger to express the steepness near threshold with the two-stage model proposed by Attneave to consider the loudness-comparison process. Equal-loudness levels are then estimated according to the following procedure. (1) Parameters of the loudness function are estimated from the experimental data by the nonlinear least-squares method. (2) The estimated parameters are smoothed along the frequency axis with B-spline functions. (3) The equal-loudness level contours are calculated by using estimated parameters and the threshold of the hearing curve. Through this procedure, the new equal-loudness level contours are determined from the experimental data obtained hitherto.