ISO 532B Research Articles

Computational model for predicting sound quality metrics using loudness model based on gammatone/gammachirp auditory filterbank and its applications

Sound quality metrics (SQMs), such as sharpness, roughness, and fluctuation strength, have been utilized to study the perceived pleasantness or unpleasantness of sounds. Computational models for predicting SQMs have been proposed, commonly based on Zwicker's loudness method (ISO 532B:1975). ISO 532 was revised in 2017; Moore & Glasberg's loudness method for stationary sound was adopted in ISO 532-2:2017, while Zwicker's loudness method for stationary and time-varying sound was revised in ISO 532-1:2017. There are a few important differenterences between the two methods, such as the frequency scale (Bark scale or ERB scale) and filter shape (symmetry or asymmetry). It therefore might be necessary to revise these computational models for predicting SQMs on the basis of these revisions. We previously proposed a time-domain computational model for predicting SQMs on the basis of a loudness method using the time-domain auditory filterbank. This loudness method can be regarded as a time-domain version of Moore & Glasberg's method in ISO 532-2:2017, using gammatone/gammachirp auditory filterbanks instead of the roex auditory filterbank, which does not have any time-domain representations. In this paper, we introduce calculations for three SQMs (sharpness, roughness, and fluctuation strength) using the proposed model for predicting SQMs.

How should we move forward with the next version of the ANSI S3.4 loudness standard?

Recent updates to the international loudness standard ISO 532 reflect both increased understanding of loudness and the use of loudness standards by the acoustics and engineering communities. Both are inspiration to consider revising ANSI S3.4-2007. The current ANSI standard is based on Moore and Glasberg’s model of loudness for stationary sounds. The new ISO 532-2 is a revision of this. The new ISO 532-1 is based on Zwicker’s time-varying loudness, and will replace the current ISO 532B, also based on Zwicker’s loudness model but for stationary sounds. For people who are not developing loudness models but are using them to assess sounds or noise, there are a number of other issues, e.g., loudness of very low frequency sounds, and exposure assessment based on loudness. These will be discussed and possible directions in updating the current ANSI standard are presented.

Acoustical topology optimization for Zwicker’s loudness model – Application to noise barriers

Traditionally, the objective of design optimization of an acoustic system is to reduce physical acoustic properties, i.e., sound pressure and power. However, since these parameters are not sufficient to present the relation of physical sound stimulus with human perceptual judgment, physical acoustic properties may not represent adequate parameters for optimizing acoustic devices. In this paper, we first present a design method for acoustical topology optimization by considering human’s subjective conception of sound. To consider human hearing characteristics, Zwicker’s loudness is calculated according to DIN45631 (ISO 532B). The main objective of this work is to minimize the main specific loudness of a target critical band rate by optimizing the distribution of the reflecting material in a design domain. The Helmholtz equation is used to model acoustic wave propagation and, it is solved using the finite element method. The sensitivity of the main specific loudness is calculated using the adjoint variable method and the chain rule. To demonstrate the effectiveness of the proposed method, various examples of noise barriers are presented with different source and receiver locations. The results obtained, using the optimized noise barriers that consider Zwicker’s loudness, are compared with the results for straight and T-shaped barriers. The results are also compared with topology optimization using 1/3-octave band level as an objective function. The optimized noise barrier using the proposed method shows the best result with respect to a human’s hearing sensation.

Evaluating Roadside Noise Barriers Using an Annoyance Reduction Criterion

The effectiveness of noise barriers is typically assessed as the reduction in A-weighted sound pressure level ( LA). This research indicates that this may not be a valid indicator of the corresponding annoyance reduction. Road traffic noise was recorded behind a noise barrier (barrier sounds) and at a location with no barrier (non-barrier sounds). The barrier sounds, recorded 10–45 m from the road, and non-barrier sounds recorded 50–200 m from the road were of similar LA. Despite this, participants in a listening experiment found the barrier sounds to be more annoying than the non-barrier sounds, an annoyance-difference corresponding to a 3-dB increase in LA. The Loudness level (ISO 532B) and a low-frequency corrected sound pressure level ( LA) were found to be better than LA as indicators of the barrier's annoyance-reduction efficiency.

Evaluating roadside noise barriers using an annoyance-reduction criterion

A common indicator of effectiveness for roadside noise barriers is the reduction in A-weighted sound pressure level (L(A)). The present experimental study considered alternative indicators using an annoyance-reduction criterion. A large number of 8 s experimental sounds were created from binaural recordings conducted at various distances from a highway at a location with a 4.6 m high roadside barrier (barrier sounds) and at a location along the same road with no barrier (nonbarrier sounds). Eighteen listeners scaled the annoyance of the experimental sounds with the method of magnitude estimation. The barrier sounds recorded 10-45 m from the road and nonbarrier sounds recorded 50-200 m from the road were of similar L(A). Despite this, the barrier sounds were found to be more annoying than the nonbarrier sounds. The annoyance difference corresponded to approximately a 3 dB increase in L(A) and was mainly related to the barrier sounds' higher relative level of low-frequency sound. This suggests that L(A) reduction may not be a valid indicator of the annoyance reduction caused by a noise barrier. The loudness level (ISO 532B) and a low-frequency corrected sound pressure level (L(A) ( *)) were found to be better than L(A) as indicators of the barrier's annoyance-reduction efficiency.

Relationships between arithmetic averages of sound pressure level calculated in octave bands and Zwicker’s loudness level

Previously it has been found through a series of psychoacoustical experiments that the arithmetic average of sound pressure level calculated in octave bands is a good estimator of loudness for various kinds of environmental noise. Remarkably, the arithmetic average of sound pressure level in octave bands from 63 Hz to 4 kHz, L m,1/1 (63–4k), strongly correlates with the loudness level specified in ISO 532B, LL( Z), as well as with loudness assessment. To investigate this relationship further, a numerical study has been carried out based on Zwicker’s loudness model. As a result, practical expressions to estimate the loudness levels of general environmental noises from the sound pressure levels in octave bands from 63 Hz or 125 Hz to 4 kHz are proposed.

Evaluation of Drum Sound with ISO Tapping Machine

A branch norm, EPLF NORM 021029-3,1 has been established for measuring drum sound on laminate floor coverings. ‘Drum sound’ refers to the sound occurring when an object, e.g. a foot, strikes the flooring in the room in which the receiving ear is located. The norm evaluates the subjective perception of the drum sound's loudness using the ISO tapping machine. A round-robin study of the norm is reported along with the results of a paired comparison listening test using the same floor coverings. The article discusses general aspects of evaluation measures, tapping machines, test environments, etc., that need to be considered when measuring drum sound on various floor coverings, such as linoleum, wood parquet and laminate. It is concluded that loudness as measured according to ISO 532B correlates the best with the subjective perception of the drum sound's loudness. The tapping machine can be used to excite hard floor coverings to produce the drum sound, but should be used with caution in studying low-level drum sounds due to the tapping machine's inherent mechanical noise.

Evaluation of loudness-level weightings for assessing the annoyance of environmental noise.

Assessment of the annoyance of combined noise environments has been the subject of much research and debate. Currently, most countries use some form of the A-weighted equivalent level (ALEQ) to assess the annoyance of most noises. It provides a constant filter that is independent of sound level. Schomer [Acust. Acta Acust. 86(1), 49-61 (2000)] suggested the use of the equal loudness-level contours (ISO 226, 1987) as a dynamic filter that changes with both sound level and frequency. He showed that loudness-level-weighted sound-exposure level (LLSEL) and loudness-level-weighted equivalent level (LL-LEQ) can be used to assess the annoyance of environmental noise. Compared with A-weighting, loudness-level weighting better orders and assesses transportation noise sources, sounds with strong low-frequency content and, with the addition of a 12-dB adjustment, it better orders and assesses highly impulsive sounds vis-a-vis transportation sounds. This paper compares the LLSEL method with two methods based on loudness calculations using ISO 532b (1975). It shows that in terms of correlation with subjective judgments of annoyance-not loudness-the LLSEL formulation performs much better than do the loudness calculations. This result is true across a range of sources that includes aircraft, helicopters, motor vehicles, trains, and impulsive sources. It also is true within several of the sources separately.

A cross-cultural study of the factors of sound quality of environmental noise

The sound quality of various environmental noises was judged using semantic differential in Japan, Germany, the U.S.A., and China. The sounds used were aircraft noise, train noise, road traffic noise, speech, music, and construction noise. As the result of factor analysis, three factors were extracted in Japan and Germany. They were interpreted as ‘‘powerful,’’ ‘‘pleasant,’’ and ‘‘metallic’’ factors. In the U.S., and China, ‘‘powerful’’ and ‘‘metallic’’ factors were not differentiated. The impression of ‘‘powerful’’ factors were found to show high correlation with LAeq and loudness level based on ISO 532B. There seemed some difference in connotative meanings of the terms ‘‘loud,’’ ‘‘noisy,’’ and ‘‘annoying’’ among the four countries. There was little difference in the impression of high-level aircraft noise, train noise, and road traffic noise among the four countries. They were perceived as negative impression such as ‘‘annoying,’’ ‘‘ugly,’’ ‘‘unpleasant,’’ etc. The validity of other psychophysical measures was examined in relation to these results.

Evaluation of broad-band noise mixed with amplitude-modulated sounds.

A series of experiments was conducted concerning the effect of amplitude-modulated (AM) sounds on the impression of broad-band noise. The following results were found:(1) AM sounds in broad-band noise were detected when S/N was around zero (S: the level of AM sound, N: 1/3 octave band level of broad-band noise with center frequency corresponding to the carrier frequency of AM sounds). Close examination showed that carrier frequency, modulation frequency and modulation depth had a systematic effect on the detection of AM sounds.(2) The loudness of broad-band noise mixed with AM sounds could be approximately evaluated by loudness level based on ISO 532B (LLz).(3) The timbre of broad-band noise mixed with AM sounds was judged to be more metallic as the carrier frequency of AM sounds became higher and to be more clamorous as the carrier frequency became lower. This suggests that the timbre is deteriorated when AM sounds are mixed with broad-band noise. The three factors were extracted by the factor analysis: they were “metallic” or “unpleasant, ” “powerful” and “rough.”

Loudness and timbre of broad-band noise mixed with frequency-modulated sounds.

A series of experiments was conducted concerning the loudness and timbre of broad bandnoise mixed with frequency-modulated sounds. The results suggested the follow ings:(1) FM sounds overlapped on broad-band noise can be just detectable when S/N is around zero (S: the level of FM sound, N: the 1/3 octave band level of broad-band noise with center frequency corresponding to carrier frequency of FM sound).(2) FM sounds overlapped on broad-band noise can be detected at S/N of-10 dB or less when it is interrupted.(3) The loudness of broad-band noise shows good correspondence with Leq. However, when a prominent frequency component, such as FM sounds, is included, loudness level based on ISO 532B (LLz) shows better correspondence than Leq.(4) The timbre becomes deteriorated when the level of specific frequency component in creasesor when its frequency becomes high. These effects were found even when the overall values of Leq were kept constant. Neither Leq nor LLz is sufficient for evaluating these effects. The method for calculating sharpness proposed by von Bismarck is an ap propriatemethod for evaluating the metallic aspect of the timbre.

Program for calculating loudness according to DIN 45631 (ISO 532B).

The method for calculating loudness level proposed by Zwicker is standardized in ISO 532B. This is a graphical procedure and it can be tedious to calculate loudness level by this procedure. Recently, DIN 45631 has been revised including a computer program for calculating loudness level in BASIC which runs on IBM-compatible PC's. Since the NEC PC-9801 series computers are popular in Japan, the program has been modified for the NEC PC-9801 series computers and is introduced in this paper.

Hearing sensations and noise quality evaluation

Noise quality can be assessed subjectively along different perceptual dimensions, called “hearing sensations.” Of particular relevance for noise quality evaluation are the hearing sensations loudness, sharpness, and fluctuation strength. The dependence of these hearing sensations on important stimulus parameters is briefly reviewed. In addition, the physical evaluation of noise quality by means of a loudness meter in accordance with ISO 532B is demonstrated. Subjective and physical noise evaluations are compared. [Work supported by DFG.]

Air-conditioner noise and noise quality

Most people would agree that air conditioners should be as quiet as possible. However, it can be shown that air-conditioner noise can have a positive effect in that it can mask other, more unwanted, noises. It is, therefore, desirable that the noise produced by air conditioners should be as acceptable as possible. A series of experiments was conducted using simulated air-conditioner noise to investigate the loudness and sound qualitites of air-conditioner noise and to examine the appropriateness of applying ISO 532B to air-conditioner noise.

Objective measures of the annoyance due to automobile passenger compartment noise

The annoyance attributable to complex noises consisting of multiple pure tones (which may or may not be harmonically related) and substantial broadband noise is not easily quantifiable. It has been shown that dBA is a poor indicator of loudness [Hellman and Zwicker, J. Acoust. Soc. Am. 82, 1700–1705 (1987)], and a number of other measures have been proposed. In this study, the results of subjective preference tests of passenger compartment noise are compared to objective measures of loudness and annoyance. Eight synthesized variations of the noise experienced at full throttle acceleration were ranked by 40 subjects according to their desirability. All samples were normalized to 101‐dB linear. These results are compared to the objective rating methods: AI (articulation index), ISO 532B (Zwicker method), Stevens Mark VII, CRP (Composite Rating of Preference), and PNL (perceived noise level). The CRP offers the best correlation with subjective results. The results of Mark VII, and ISO 532B are markedly improved by the addition of empirically derived corrections.