ISO 226 loudness countours (pysdm.iso226)

Loudness contours from ISO 226.

Contours are returned both as tables of data and as contour functions

Functions returning ISO 226 contours

iso226_spl_contour([L_N, hfe])

Generates an equal loudness contour as described in ISO 226.

iso226_spl_itpl([L_N, hfe, k])

Generates an interpolation of an equal loudness contour.

Functions computing loudness/acoustic pressure

tabled_L_p(L_N[, hfe])

Table of sound pressure levels for given loudness in ISO 226.

tabled_L_N(L_p[, hfe])

Table of perceived loudness levels for given sound pressure in ISO 226.

Functions returning data tabled in the standard

tabled_f([hfe])

Table of frequencies in ISO 226.

tabled_alpha_f([hfe])

Table of exponents for loudness perception in ISO 226.

tabled_L_U([hfe])

Table of magnitudes of the linear transfer function in ISO 226.

tabled_T_f([hfe])

Table of thresholds of hearing in ISO 226.

Notes

This module uses data from the latest revision of ISO 226 [1]. For reference, also consider [2].

The ISO standard provides the equal loudness contours as tabled data. Tables end at 12.5 kHz. Above this frequency equal-loudness-level data are relatively scarce and tend to be variable [3]. Yet, it is known that the human ear has a precipitous decline in sensitivity with increasing frequency above 15 kHz, to the point that at about 20 kHz the percieved sound becomes negligible (> 100 dB attenuation) [4]. For this reason, this module includes the possibility of delivering some modified ISO contours where the tabled data is augmented by creating a new data point at 20 kHz where the behavior found at 20 Hz is replicated.

1

ISO 226:2003 “Acoustics - Normal equal-loudness-level contours”

2

Jeff Tackett, “ISO 226 Equal-Loudness-Level Contour Signal,” 2005 (http://www.mathworks.com/matlabcentral/fileexchange/7028)

3

Yoiti Suzuki et al, “Precise and Full-range Determination of Two-dimensional Equal Loudness Contours,” 2003 (http://www.nedo.go.jp/itd/grant-e/report/00pdf/is-01e.pdf)

4

Robert A. Wannamaker “Psychoacoustically Optimal Noise Shaping”, J. Audio Eng. Soc., Vol. 40, N. 7/8, 1992 July/August