The acoustic loudness calculation according to Zwicker method was introduced as a standard in the 1975 version of ISO 532 (as method B). In 1991, the DIN 45631 standard proposed an implementation of the ISO 532:1975 method B with specific corrections to match the equal loudness contours of ISO 226:1987. In 2017, this method is included in the revision of ISO 532 (as section 5 of part 1, dedicated to Zwicker method). Note that, for normative continuity, the method is still in accordance with ISO 226:1987 equal loudness contours (instead of newer ISO 226:2003 definition).
In MOSQITO, the code is based on the BASIC program published in Zwicker and Fastl, 1991.
The ISO 532-1:2017 standard provides a set of synthetic and technical signals covering representative applications to be used to validate any of its implementation. The standards also provides the compliance requirements.
The test signal n°1 (annex B2 of the standard) provides third octave levels to be used as input for stationary loudness calculation.
The test signals n°2 to 5 (annex B3 of the standard) provides .wav files to be used as input for stationary loudness calculation. A step by step description of how to use MOSQITO to calculate the loudness and the specific loudness from signal n°5 is given in this tutorial.
The plots below compares the MOSQITO loudness calculations for all the tests signals to the compliance requirements of the standards.
Loudness calculation for ISO 532-1 test signal n°1 (machinery noise in free field)
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Loudness calculation for ISO 532-1 test signal n°2 (250 Hz tone in free field with a level of 80 dB)
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Loudness calculation for ISO 532-1 test signal n°3 (1 kHz tone in free field with a level of 60 dB)
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Loudness calculation for ISO 532-1 test signal n°4 (4 kHz tone in free field with a level of 40 dB)
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Loudness calculation for ISO 532-1 test signal n°5 (pink noise in free field with an overall level of 60 dB)
All the validation plots and scripts can be found in this folder.
DIN 45631:1991, Berechnung des Lautstärkepegels und der Lautheit aus dem Geräuschspektrum; Verfahren nach E. Zwicker (Calculation of loudness level and loudness from the sound spectrum; Zwicker method)
ISO 226:1987, Acoustics — Normal equal-loudness-level contours
ISO 226:2003, Acoustics — Normal equal-loudness-level contours
ISO 532:1975, Acoustics — Method for calculating loudness level
ISO 532-1:2017, Acoustics — Methods for calculating loudness — Part 1: Zwicker method
Zwicker E., Fastl H. Program for calculating loudness according to DIN 45631 (ISO 532B). J.A.S.J 1991, (E) 12, 1