Annoyance of noise stimuli in relation to the spatial factors extracted from the interaural cross-correlation function

While considering auditory-brain model for subjective responses, effects of spatial factors extracted from the interaural cross-correlation function (IACF) on annoyance of noise stimuli are examined. The previously developed indices to measure sound pressure levels (SPL) and frequency characteristics cannot fully explain the psychological effects of noise. In the first experiment, subjects judged their annoyance by changing fluctuations in the magnitude of interaural cross-correlation function (IACC) and the SPL. In the second, they judged their annoyance by changing fluctuations in the interaural time delay (τ_IACC) and the SPL. Results show that: (1) annoyance increased by increasing the fluctuations of IACC as well as the SPL, (2) annoyance increased by increasing the fluctuations of τ_IACC as well as the SPL.     

DIAGNOSTIC SYSTEM BASED ON THE HUMAN AUDITORY-BRAIN MODEL FOR MEASURING ENVIRONMENTAL NOISE—AN APPLICATION TO RAILWAY NOISE

Measurements of railway noise were conducted by use of a diagnostic system of regional environmental noise. The system is based on the model of the human auditory-brain system. The model consists of the interplay of autocorrelators and an interaural crosscorrelator acting on the pressure signals arriving at the ear entrances, and takes into account the specialization of left and right human cerebral hemispheres. Different kinds of railway noise were measured through binaural microphones of a dummy head. To characterize the railway noise, physical factors, extracted from the autocorrelation functions (ACF) and interaural crosscorrelation function (IACF) of binaural signals, were used. The factors extracted from ACF were (1) energy represented at the origin of the delay, Φ (0), (2) effective duration of the envelope of the normalized ACF, τe, (3) the delay time of the first peak, τ₁, and (4) its amplitude,ø₁ . The factors extracted from IACF were (5) IACC, (6) interaural delay time at which the IACC is defined, τ_IACC, and (7) width of the IACF at the τ_IACC,W_IACC . The factor Φ (0) can be represented as a geometrical mean of energies at both ears as listening level, LL.     

DISSIMILARITY JUDGMENTS IN RELATION TO TEMPORAL AND SPATIAL FACTORS FOR THE SOUND FIELD IN AN EXISTING HALL

In relation to the temporal and spatial factors of sound fields, dissimilarity judgments for different source locations on a stage were performed. This study is based on the model of the auditory-brain system, which consists of the autocorrelation and crosscorrelation mechanisms for sound signals arriving at two ears and the specialization of human cerebral hemispheres. There are three temporal factors (τ₁,φ₁ and τ_e) extracted from the autocorrelation function and four spatial factors (LL,IACC,τ_IACC and W_IACC) from the interaural crosscorrelation function of binaural signals. In addition to these temporal and spatial factors, the orthogonal factors of the subjective preference for sound field (Δt₁ and T_sub) were taken into account. The psychological distance between sound fields of different source locations on the stage were calculated by using these temporal, spatial and orthogonal factors of sound fields. Using these distances and their linear combination, dissimilarity can be calculated. Results of multivariable analysis show that the calculated scale values of dissimilarity agree well with the measured scale values.     

SUBJECTIVE PREFERENCE FOR SOUND SOURCES LOCATED ON THE STAGE AND IN THE ORCHESTRA PIT OF AN OPERA HOUSE

The present study investigates whether the subjective preference theory can be applied to the sound field in an opera house. Paired-comparison tests were conducted to obtain scale values of subjective preference. As the source locations of the music on the stage and in the orchestra pit were moved, listeners were asked to give their acoustical preference. The acoustical factors at each listening position were obtained from the interaural cross-correlation function and binaural impulse responses measured at each listening position. The relationship between the scale values of subjective preference and orthogonal acoustical factors (LL, IACC, τ_IACC, Δt₁ for the pit source, Δt₁ for the stage, T_sub for the pit source, and T_sub for the stage source) was determined by using factor analysis, which shows that the preference theory is applicable. Total scores obtained from factor analysis and measured scale values are in good agreement.     

Characteristics of train noise in above-ground and underground stations with side and island platforms

Railway stations can be principally classified by their locations, i.e., above-ground or underground stations, and by their platform styles, i.e., side or island platforms. However, the effect of the architectural elements on the train noise in stations is not well understood. The aim of the present study is to determine the different acoustical characteristics of the train noise for each station style. The train noise was evaluated by (1) the A-weighted equivalent continuous sound pressure level (L_Aeq), (2) the amplitude of the maximum peak of the interaural cross-correlation function (IACC), (3) the delay time (τ₁) and amplitude (?₁) of the first maximum peak of the autocorrelation function. The IACC, τ₁ and ?₁ are related to the subjective diffuseness, pitch and pitch strength, respectively. Regarding the locations, the L_Aeq in the underground stations was 6.4 dB higher than that in the above-ground stations, and the pitch in the underground stations was higher and stronger. Regarding the platform styles, the L_Aeq on the side platforms was 3.3 dB higher than on the island platforms of the above-ground stations. For the underground stations, the L_Aeq on the island platforms was 3.3 dB higher than that on the side platforms when a train entered the station. The IACC on the island platforms of the above-ground stations was higher than that in the other stations.     

A STUDY OF THE BLENDING OF VOCAL MUSIC WITH THE SOUND FIELD BY DIFFERENT SINGING STYLES

The initial time delay Δt₁ between the direct sound and the first reflection and the subsequent reverberation time T_sub are usually fixed within a given space. Thus, concert halls do not have ideal conditions for all forms of music. It has been shown that the most preferred conditions for both listeners and performers are determined by the minimum value of the effective duration of the running autocorrelation function (ACF) of sound signals, (τ_e)_min. To determine the suitability of vocal music for a given sound field, (τ_e)_min of vocal music was analyzed, after recording five solo singers (tenor) in an anechoic room. The results showed that (τ_e)_min of the ACF of a voice source, which is closely related to the two temporal factors of the sound field, varies with singing style. A significant finding is that the values of (τ_e)_min of sound signals forfalsetto and medium falsetto are significantly longer than that for operatic singing.     

Nonlinear response in evaluating the subjective diffuseness of sound fields

Tests were conducted to determine which horizontal reflection angles are most effective in stimulating subjective diffuseness for a listener in a room. Paired comparison tests were carried out where subjects were asked to judge in which of two sound fields they perceived more diffuseness. Results show that the most effective horizontal angle depends on the frequency of the one-third-octave-band noise, as is indicated by the interaural cross correlation. The remarkable finding in this investigation is that the scale value of subjective diffuseness may be formulated in terms of the 3/2 power of the magnitude of interaural cross correlation (IACC) and that the scale value does not vary with the frequency of the bandpass noise source.     

CORRELATION FACTORS DESCRIBING PRIMARY AND SPATIAL SENSATIONS OF SOUND FIELDS

The theory of subjective preference of the sound field in a concert hall is established based on the model of human auditory-brain system. The model consists of the autocorrelation function (ACF) mechanism and the interaural crosscorrelation function (IACF) mechanism for signals arriving at two ear entrances, and the specialization of human cerebral hemispheres. This theory can be developed to describe primary sensations such as pitch or missing fundamental, loudness, timbre and, in addition, duration sensation which is introduced here as a fourth. These four primary sensations may be formulated by the temporal factors extracted from the ACF associated with the left hemisphere and, spatial sensations such as localization in the horizontal plane, apparent source width and subjective diffuseness are described by the spatial factors extracted from the IACF associated with the right hemisphere. Any important subjective responses of sound fields may be described by both temporal and spatial factors.     

THE PREFERRED INITIAL TIME DELAY GAP AND INTER-AURAL CROSS CORRELATION FOR A JAVANESE GAMELAN PERFORMANCE HALL

This paper discusses the application of a method based on human subjective preference to the acoustic design of a Javanese gamelan performance hall. Some important distinctions between Javanese gamelan ensembles and Western classical orchestra are the tuning system, orchestral blending process, and technique of playing. The results of subjective preference test using the rank order method showed that the subjects preferred 24·25 ms for the initial time delay gap (ITDG) and the smallest value of the inter-aural cross-correlation (IACC). The preferred ITDG agree with the ITDG from the room response measured in a traditional pendopo in Indonesia, which is not a common concert hall but an open-sided hall. However, the preferred IACC is not in agreement with the measured ITDG in thependopo .     

Magnetoencephalographic responses correspond to individual annoyance of bandpass noise

The relation between human brain responses to an individual's annoyance of bandpass noise was investigated using magnetoencephalography (MEG) measurements and analysis by autocorrelation function (ACF) and cross-correlation function (CCF). Pure tone and bandpass noises with a centre frequency of 1000 Hz were used as source signals. The sound pressure level was constant at 74 dBA and the duration of the stimulus was 2.0 s. The scale values of annoyance for each subject were obtained by paired-comparison tests. In MEG measurements, the combination of a reference stimulus (pure tone) and test stimuli (bandpass noise) was alternately presented 30 times at a constant 2 s interstimulus interval. The results show that the effective duration of the ACF, τ_e, of MEG in the 8-13 Hz range, which represent repetitive features within the signal itself, became shorter during the presentation of an annoying stimulus. Also, the maximum value of the CCF, |φ(τ)|_max, became smaller. The shorter τ_e and smaller |φ(τ)|_max indicate that a wider area of the brain is unstable for longer with annoying auditory stimuli.     

Über die gewünschte hörerlautstärke bei kammermusik

One of the acoustic criteria that have a major influence on the auditory experience during a concert is that of volume. This is something that is not always felt to be satisfactory, especially among chamber music audiences. It is not yet known, however, which volume levels listeners of chamber music pieces consider to be desirable. By means of suitable listening experiments, an attempt was made to find an answer to this question.In a medium-sized auditorium, comparable in size to a small chamber music hall, individual listeners were played excerpts from various pieces of chamber music. Each listener was requested to adjust the volume to what he or she felt to be the optimal level. The following values were then measured for each excerpt: the equivalent continuous sound level L_eq, the mean maximum level L_1% and the lower limiting level L_95%. The measurements, which covered a sample of 24 people, show that:

1. 1.1.|There are clear upper and lower limits for acceptable sound volume levels.
2. 2.2.|The preferred volume levels can differ considerably within these limits.
3. 3.3.|There is an individual volume range for each individual listener.
4. 4.4.|A volume with an equivalent continuous sound level L_eq around 70 dB(A) is the single most satisfactory level for listeners overall.

     

A neural-computation method of predicting the early interaural cross-correlation coefficient (IACCE3) for auditoria

A method of predicting the early interaural cross-correlation coefficient (IACC_E3) in unoccupied concert halls has been investigated using neural network analysis. Constructional and acoustical data for 36 unoccupied concert halls, in various countries, were utilized for the neural network analyses. A neural network for calculating IACC_E3 has been embedded in a standard spreadsheet application so that designers and researchers, without access to specialized neural network software can use the results of the present work. Investigations using the neural network model have shown that IACC_E3 predictions are within the subjective difference limen, which is 0.075±0.008. Five concert halls were used to assess the neural network analysis method and the errors between measured and predicted (1−IACC_E3) ranged from −0.05 to 0.02. These results indicate that there is a good basis for using trained neural networks to predict IACC_E3.     

MAGNETOENCEPHALOGRAPHIC RESPONSES CORRESPONDING TO INDIVIDUAL SUBJECTIVE PREFERENCE OF SOUND FIELDS

To investigate human cortical responses that correspond to subjective preference of sound fields, an attempt is made here to analyze the autocorrelation function (ACF) of magnetoencephalography (MEG) under the condition of varying delay time of single reflections. According to previous studies, it is assumed that a similar repetitive feature of the MEG alpha-waves range (8-13 Hz) is related to subjective preference in terms of the effective duration of the ACF. The source signal was the word “piano” which had a 0·35 s duration. The delay time, Δt₁, was varied at five levels (0, 5, 20, 60, and 100 ms). The scale values of the subjective preference of each subject were obtained by the paired-comparison tests. To compare the results of the MEG measurements with the scale values of the subjective preference, combinations of a reference stimulus (Δt₁=0 ms) and test stimuli (Δt₁=0, 5, 20, 60, and 100 ms) were presented alternately 50 times, and the MEGs were analyzed. It is found that subjective preference for each individual and the effective duration of the ACF of the MEG alpha waves are linearly related.     

LOUDNESS OF SHARPLY (2068 dB/OCTAVE) FILTERED NOISES IN RELATION TO THE FACTORS EXTRACTED FROM THE AUTOCORRELATION FUNCTION

This study examines the loudness of bandpass noises with center frequencies of 250, 500 and 1000Hz while changing the autocorrelation function (ACF). The bandwidth of the source signal was altered with a 2068 dB/octave sharp filter to control the ACF of the source signal. The scale values of loudness were obtained using a paired-comparison method. It is shown that the loudness of the bandpass noises inside the critical band is not constant. The loudness of the pure tone is greater than that of sharply filtered noises. The loudness of the bandpass noises increases with increasing effective duration of the ACF (τ_e) of the source signal.     

TEMPORAL AND SPATIAL ACOUSTICAL FACTORS FOR LISTENERS IN THE BOXES OF HISTORICAL OPERA THEATRES

Acoustical measurements were conducted in a horseshoe-shaped opera house to clarify the acoustical quality of a sound field for listeners inside the boxes of an historical opera house. In order to investigate the effects of multiple reflections between the walls inside a box and scattering by the heads of people, the location of the receiver and the number of persons in the box were varied. In each configuration, four orthogonal factors and supplementary factors were derived as temporal and spatial factors by analysis of binaural impulse responses. Each factor is compared to that at a typical location in the stalls of the same theatre. An omni-directional sound source was located on the stage to emulate a singer or in the orchestra pit to reproduce the location of the musicians. Thus, in this paper, temporal and spatial factors in relation to subjective evaluation are characterized against changes in the listening conditions inside a box, and procedures for improvement and design methods for boxes are proposed. The main conclusions reached are as follows. As strong reflections from the lateral walls of a hall are screened by the front or side walls of a box for a receiver in a seat deeper in the box, the maximum listening level (LL) in the boxes was observed at the front of the box, and the maximum range of LL values for each box was found to be 5 dB. Concerning the initial time delay gap (Δt₁), a more uniform listening environment was obtained in boxes further back in the theatre than in one closer to the stage. The subsequent reverberation time (T_sub) lengthens for boxes closer to the stage due to the stage house with its huge volume, and a peak is observed at 1 kHz. For the box at the back, T_sub monotonically decreases with frequency in the same way as in the stalls, and moreover, its values approach those in the stalls. As the contribution of multiple reflections relatively increases for a receiver deeper in the box, the IACC in such positions decreases in comparison with that seen at the front of the box.     

Sound strength and reverberation time in small concert halls

Sound strength and reverberation time measurements have been carried out in six small concert halls in Cambridge, UK. The sound strength G is a measure of the physical sound level in a concert hall and is closely related to the subjective sensation of loudness. It compares integrated impulse responses at a point in the measured room with that measured at ten metres distance in the free field.The aim of the measurements is to investigate the acoustic characteristics of the halls concerning sound strength and reverberation time. Furthermore the effect of the variable acoustics in the halls on these parameters is discussed in this paper. Especially for bigger ensembles it is often desirable to reduce the sound level in a small concert hall. The measurement results show that for a fixed hall volume, this can primarily be achieved by decreasing the reverberation time in the hall. However, with regard to the sound quality of a hall and the recommended reverberation times for chamber music, reverberation time cannot be reduced by an arbitrary extent. Therefore reverberation time and strength have to be balanced very carefully in order to obtain sufficient reverberation whilst at the same time avoiding excessive loudness. Finally the measured strength levels are compared to values derived from traditional and revised theory [Barron M, Lee L-J. Energy relations in concert auditoriums. J Acoust Soc Am 1988;84(2):618-28] on strength calculations in order to assess the accuracy of the theory for small chamber music halls. Possible reasons for the low measured strength levels observed are discussed with reference to related design features and objective acoustic parameters.     

Psychological experiments on listener envelopment when both the early-to-late sound level and directional late energy ratios are varied, and consideration of calculated LEV in actual halls

The purposes of this paper are to clarify the relation between listener envelopment (LEV) and two physical factors, namely, early-to-late sound level C₈₀ and directional late energy ratios (DLRs), and to demonstrate the significance of evaluating LEV using C₈₀ and DLRs. Firstly, two psychological experiments are performed. In the first experiment, the results show that the previous findings about the effects of late reflections from lateral, overhead, and behind the listener on LEV are valid when they also consist of plural directional energy components, as are found in real sound fields. In the second experiment, the relational equation among LEV, C₈₀, and DLRs is derived from results when the physical factors are simultaneously varied. Secondly, psychological scores for LEV are calculated in actual halls by applying measured values for C₈₀ and DLRs to the equation. The results show that the differences in LEV among different seating positions and in the spatial uniformity of LEV among different halls are expected to be significantly large depending on the values of C₈₀ and DLRs. This suggests the significance of evaluating LEV by means of C₈₀ and DLRs.     

An experimental study on loudness evaluation of early reflections

I.IntroductionLoudnessisoncofthedistinguishingcharacteristicsinauditoriumacoustics,buthasreceivedlessattentionthanotherparametersinthepast.Genera11ytheresu1tingloudness,orthetotalenergylevelofasteadysoundsourceinahallcanbesimplypredictedbythesumofthedircctsoundandthcreverberantsound.Asspeechandmusic,areoftransicntcharacteristics,theperceivedloudnessinahallismorecomplicatedandthustheaboveprc-dichonisnottrue.Accordingtotheintegratingabilityoftheear,onlythcdirectsoundandthecarlyreflections,i.c.,…     

DURATION SENSATION WHEN LISTENING TO BANDPASS NOISES

The duration sensation of bandpass noise was examined while changing the factors (τ₁, φ₁and τ_e) extracted from the autocorrelation function. The white noise and bandpass noises with six center frequencies (125, 250, 500, 1000, 2000 and 4000 Hz) with different bandwidths were used as stimuli. A paired-comparison test comparing the white-noise duration with bandpass-noise duration was conducted under the conditions of constant sound pressure level (SPL; 80 dB(A)) and rise and fall times (1 ms). Results indicate that the duration of bandpass noise is judged to be longer than that of the white noise. The duration sensation of the bandpass stimuli with longer τ₁is significantly longer than that of the stimuli with shorterτ₁ (p<0·01).