ISO/TC 43/WG 9 - Method for calculating loudness level

This document specifies a method for estimating the loudness and loudness level of both stationary and time-varying sounds as perceived by otologically normal adult listeners under specific listening conditions. The sounds may be recorded using a single microphone, using a head and torso simulator, or, for sounds presented via earphones, the electrical signal delivered to the earphones may be used. The method is based on the Moore-Glasberg-Schlittenlacher algorithm. NOTE 1 Users who wish to study the details of the calculation method can review or implement the source code which is entirely informative and provided with the standard for the convenience of the user. This method can be applied to any sounds, including tones, broadband noises, complex sounds with sharp line spectral components, musical sounds, speech, and impact sounds such as gunshots and sonic booms. Calculation of a single value for the overall loudness over the entire period of a time-varying signal lasting more than 5 s is outside the scope of this document. NOTE 2 It has been shown that, for steady tones, this method provides a good match to the contours of equal loudness level as defined in ISO 226:2003[18] and the reference threshold of hearing as defined in ISO 389-7:2019[19].

ISO 532-2:2017 specifies a method for estimating the loudness and loudness level of stationary sounds as perceived by otologically normal adult persons under specific listening conditions. It provides an algorithm for the calculation of monaural or binaural loudness for sounds recorded using a single microphone, using a head and torso simulator, or for sounds presented via earphones. The method is based on the Moore-Glasberg algorithm. NOTE 1 Issues of binaural calculations are discussed in Annex A. NOTE 2 Users who wish to study the details of the calculation method can review or implement the source code, which is entirely informative and provided with ISO 532-2:2017 for the convenience of the user. This method can be applied to tones, broadband noises and complex sounds with sharp line spectral components, for example transformer hum or fan noise. NOTE 3 It has been shown (see Reference [15]) that this method provides a good match to the contours of equal loudness level as defined in ISO 226:2003 and the reference threshold of hearing as defined in ISO 389‑7:2005. The evaluation of the harmful effect of sound events is outside the scope of ISO 532-2:2017.

ISO 532-1:2017 specifies two methods for estimating the loudness and loudness level of sounds as perceived by otologically normal persons under specific listening conditions. The first method is intended for stationary sounds and the second method for arbitrary non-stationary (time-varying) sounds, including stationary sounds as a special case. The methods can be applied to any sound recorded as single-channel measurements using a microphone, or as multi-channel measurements, for example by means of a head and torso simulator (see Annex D). Since most important technical sounds are time-varying, a model of time-varying loudness is preferable. The methods are based on the Zwicker algorithm.[14] The method for stationary sounds is provided for reasons of continuity and also offers the use of measured one-third-octave-band levels as input. The more general method for arbitrary sounds calculates the specific loudness pattern based on measured time signals by applying a signal processing model that is directly related to physiological and psychological characteristics of the human hearing system. Loudness is calculated from the specific loudness pattern. It has been shown that this method provides a good match to the results of many loudness experiments using synthetic and technical sounds. No prior knowledge about the properties of the sound (e.g. broadband or narrowband noise, tonal content) and no user interactions are required for the fully automated application of the method. The evaluation of the harmful effect of sound events is outside the scope of ISO 532-1:2017.