Listener Envelopment Research Articles

오디오 컨텐츠를 위한 비음수 행렬 분해 기법 기반의 실시간 단일채널 배경 잡음 추출 기법

본 논문에서는 비음수 행렬 분해 (NMF) 기법을 이용하여 단일 채널에서 배경음 성분을 추출하는 알고리즘에 대해 서술한다. 이러한 배경음 성분 추출은 오디오 업믹싱 시스템을 고려하여 개발되었으며, 기존의 연구를 통하여 분리된 배경음 신호가 업믹싱 시스템에 적용될 경우 공간감을 향상시킬 수 있다는 사실이 이미 확인된 바 있다. 다만 기존의 기법은 음향 신호를 모두 축적하여 일괄적으로 처리해야 한다는 단점이 있어, 스트리밍 시스템이나 디지털 시그널 프로세서 (DSP) 등을 이용한 시스템에서 사용되기 어렵다. 본 논문에서는 이를 해소하기 위하여 실시간 비음수 행렬 분해 기법을 이용한 배경음 추출 시스템을 고안하여 실험하였다. 실험에서 처리된 음원을 스펙트럼 평활도를 이용하여 분석한 결과, 고안된 배경음 추출 시스템이 기존의 일괄 추출 시스템과 유사한 정도로 배경음 성분을 추출했음을 확인할 수 있었다. In this paper, monaural ambient component extraction algorithm based on nonnegative matrix factorization (NMF) is described. The ambience component extraction algorithm in this paper is developed for audio upmixing system; Recent researches have shown that they can enhance listener envelopment if the extracted ambient signal is applied into the multichannel audio upmixing system. However, the conventional method stores all of the audio signal and processes all at once, so it cannot be applied to streaming system and digital signal processor (DSP) system. In this paper, the ambient component extraction algorithm based on on-line nonnegative matrix factorization is developed and evaluated to solve the problem. As a result of analysis of the processed signal with spectral flatness measures in the experiment, it was shown that the developed system can extract the ambient signal similarly with the conventional batch process system.

Influence of manipulated early reflections on room acoustical perception

The binaural room impulse response (BRIR) can be used to study the perception of room acoustics and consists of different parts such as the direct sound, early and late reflections, and a diffuse reverberant tail. For this study, the contribution of early reflections to several perceptual attributes was investigated. For this purpose, the strength of the early reflections of recorded BRIRs were either increased or decreased. The resulting BRIRs as well as the original BRIRs have then been convolved with anechoic music signals to obtain the stimuli that were presented to the subjects in a psychoacoustic experiment. The subjects had to rate the spatial impression of these manipulated and none-manipulated signals for the perceptual attributes “Listener envelopment,”” Apparent source width,” “Distance” and “Presence.” In addition to determining the influence of manipulated early reflections on the spatial impression of a room, also a comparison was made with the perceptual effect of an artificial increase of the interaural cross-correlation. Results indicate that the perceived source width increases with increasing level of the early reflections. The effect of the level manipulations on the listener envelopment seems to be small compared to the influence of the cross-correlation.

Investigation of subjective components of overall acoustic quality using binaural recordings made in Hartford's Belding Theater

Previous research in concert hall acoustics has established correlations between listener preference for overall acoustic quality (OAQ) and a number of other subjective factors. A subjective study was conducted to determine the relative importance of several characteristics to OAQ. Subjects evaluated 18 signals based on listener envelopment, reverberance, tonal quality, and overall preference using five-point rating scales. The signals were presented individually over headphones. A total of 32 subjects with formal musical training and normal hearing were included in the study. Following a brief tutorial and training session, the test was divided into four sets, one for each of the subjective factors. All of the signals and sets were presented to each subject in a random order. The binaural recordings were made in the Belding Theater in Hartford, Connecticut. A loudspeaker on the stage played three short classical motifs that were recorded in three seat locations with two distinct settings of the hall’s variable acoustics system. The sound pressure levels of all signals were normalized to isolate the characteristics of interest. The data analysis identified relationships between the three factors and OAQ, with the most significant relationship between OAQ and tonal quality. [Work was supported by NSF Grant 1302741.]

Concert rooms' quality for classical music

Finding a parameter which allows establishing if a concert room is good for orchestral classical music performances or not is one of the main interests in room acoustics. However, rooms are usually characterized by average values of some acoustic parameters. From the optimal values mostly recognized, specialists can consider a room adequate or not for a certain use. In recent works, we have obtain we have obtained a model for classifying a room for classical music performances, from the reverberation time (T30), the lateral energy factor coefficient (LFC) and the listener envelopment (LEV). From this model, we can determine the quality maps for these rooms. In this paper, we show the quality maps for five rooms. From these results we can deduce some basic rules to define a good acoustic design.

Neuroacoustics: Study on the Perception of Stereo Reverberant Sound Field at Cortical Level

On the basis of the Ando's brain hemispheric specialization auditory model, spatial information is processed in the right hemisphere. When hearing a complex sound stimuli, like a monaural sound source reproduced in a reverberant sound field, several independent acoustic cues are processed in both hemispheres simultaneously. To study the brain specialization perceiving these types of sounds, it was developed the Auditory Evoked Potentials analysis for 2000 ms after the first 80 ms from the sound onset, even though the first 300 ms is normally analyzed, and Cortical Activity descriptors, which were applied to Mismatch Negativity electro-physiological signals taken from Left and Right hemispheres. It was possible to measure the specialization of hemispheres by using two different monaural and anechoic sound sources, one with a minimum effective duration of its autocorrelation function (tau e) as low as 0.2 ms and another with minimum tau e of 190ms, both embedded into the same reverberant sound field and reproduced thru headphones. This study opens the possibility to measure the perception of listener envelopment to further develop a subjective descriptor.

The effect of using matched, but not individualized, head related transfer functions on the subjective evaluation of auralizations

Head related transfer functions (HRTFs) are a key component when creating auralizations used in subjective concert hall studies. An average HRTF, rather than an individualized HRTF, is often used when creating auralizations, which can lead to front-back ambiguity and reduced out-of-head sound localization. The goal of this study was to determine how the choice of HRTF can impact subjective impression of various concert hall acoustic qualities from auralizations. Using 10 HRTFs from the CIPIC database, the best and worst case HRTFs were determined for each test subject, based on out-of-head localization. For the main test, auralizations were created using these two HRTFs, along with an average HRTF. The subjects’ task was to evaluate the auralizations based upon concert hall acoustics characteristics, such as reverberance and listener envelopment. Before participating in the main part of the study, the subjects were required to complete a series of training sessions. Test subjects were limited to trained musicians and those who met a 15 dB hearing level requirement. The resulting data were analyzed to determine the significance of the differences between the three cases. The results from the listening tests and the statistical analysis will be presented. [Work supported by NSF Grant 1302741.]

The Influence of Early Sound Direction on Apparent Source Width (ASW)

t is now generally accepted that there are two spatial effects in concert halls: apparent source width (ASW) and listener envelopment (LEV). Barron have proposed the early lateral sound energy fraction (LFE) as an objective measure for apparent source width. But this measure takes no account of asymmetry role between the early sounds from front and behind. The purpose of this study is to investigate the relation between the arrival direction of early sound and ASW. Experiments using sound field simulated in an anechoic room confirm that early-arriving sound from in front of listener give more contribution to ASW than symmetrical direction behind listener. As the direction of arrival approaches between 45o to 60o from straight ahead in the horizontal plane the ASW approaches a maximum.

Neuroacoustics: Study on the perception of stereo reverberant sound field at cortical level

On the basis of the Ando's brain hemispheric specialization auditory model, spatial information is processed in the right hemisphere. When hearing a complex sound stimuli, like a monaural sound source reproduced in a reverberant sound field, several independent acoustic cues are processed in both hemispheres simultaneously. To study the brain specialization perceiving these types of sounds, it was developed the Auditory Evoked Potentials analysis for 2000 ms after the first 80 ms from the sound onset, even though the first 300 ms is normally analyzed, and Cortical Activity descriptors, which were applied to mismatch negativity electro-physiological signals taken from left and right hemispheres. It was possible to measure the specialization of hemispheres by using two different monaural and anechoic sound sources, one with a minimum effective duration of its autocorrelation function (tau e) as low as 0.2 ms and another with minimum tau e of 190 ms, both embedded into the same reverberant sound field and reproduced through headphones. This study opens the possibility to measure the perception of listener envelopment to further develop a subjective descriptor.

Objective and subjective differences between adjacent seats in a multipurpose hall

The purpose of this study was to evaluate differences between adjacent seats in terms of objective measures and subjective perception based on measurements and recordings taken in a mid-sized multipurpose hall. The work is based on the hypothesis that minimal differences should be found between nearby seats. Measurements were taken in three groups of nine adjacent seats. The differences between seats were analyzed in terms of the number of just noticeable differences (JNDs), using 1 dB for strength (G), 5% for early decay time (EDT) and 1 dB for clarity index (C80). The average differences between adjacent seats within a given group were approximately 2.5 JNDs for G, 4 JNDs for EDT and 2.5 JNDs for C80, which implies that these differences might be audible. However, these differences may be within measurement error. Differences in late lateral energy level (GLL), a measure of listener envelopment (LEV), were all less than 1 dB. A total of 35 test subjects were presented binaural recordings from two seat groups and were asked to evaluate LEV and acoustical quality. In general, subjects did not perceive differences between the recordings as hypothesized, with the exception of two cases where differences in LEV were statistically significant.

Spatial impressions from late overhead reflections in concert halls

It is known that not only late lateral reflections but also late overhead reflections contribute to listener envelopment (LEV) which is one of the perceptive factors in the spatial impression of sounds in a concert hall. This paper describes results of psychological experiments which are intended to clarify differences between spatial impressions of the late overhead reflections and that of the late lateral reflections. The results are the following: (1) Late overhead reflections have a different acoustic effect from late lateral reflections. (2) Late overhead reflections increase not only LEV but also overhead sound image (OSI). (3) Late lateral reflections contribute mainly to horizontal listener envelopment (HLEV). (4) If OSI is increased in addition to HLEV, a listener feels vertical listener envelopment (VLEV).

45 years of spatial impression

The story of spatial hearing has a certain circularity about it. To date, two separate spatial effects have been identified. The first effect is that created by a reverberant field in an enclosure, which is particularly obvious in a cathedral-type space. A second spatial effect was proposed 45 years ago linked to early lateral reflections. These two are now known as Listener Envelopment (LEV) and Source Broadening (or Apparent Source Width, ASW). Interesting research had been conducted into “Raumlichkeit” in Germany during the '60s. But following the revelations by Marshall, interest in the effects of early lateral reflections overshadowed interest in what is now called LEV. Sound level also contributes to the magnitude of these spatial effects. Measures have been proposed for both ASW and LEV, which include both reflection directional distribution and sound level. The paper will summarise the history of spatial impression and what implications it has for concert hall design. Historical reference: Applied Acoustics (2001) 62, 91-108 and 185-202.

On the Influence of sampling errors on the perception of spatial sound fields using spherical microphone arrays for auralization

Spherical microphone distributions allow a three dimensional sampling of the sound field in a room. These microphone array data can be used for auralization on various playback systems. The aim of auralization is the reproduction of the sampled spatial sound field in order to give the listener the impression of being in the measured room. Due to the discrete spatial sampling process spatial aliasing corrupts the measured data. Therefore the resulting auralization quality is affected in terms of its spatial characteristics. Subjective quality measures for the spaciousness of sound fields can be represented by source localization accuracy, the apparent source width (ASW) and the listener envelopment (LEV). These subjective features are strongly related to objective measures like interaural level and time differences (ILD and ITD) or the interaural cross correlation (IACC). In subjective listening tests the influence of sampling errors on the binaural reproduction of a sampled sound field is investigated. The results are correlated with ITD, ILD and with IACC in order to gain an objective quality measure for sound fields recorded wtih spherical microphone arrays. The investigations are based on real measurement data taking various directions of arrival and different rooms into account.

Perceptual control of convolution based room simulators

Reverberation processing has been intensively studied in audio and acoustics research for many years now. Early approaches used feedback delay networks to control the temporal distribution of reflections and to simulate the statistical properties of room reverberation. Thanks to the increase in processing power and the development of low-latency convolution algorithms a new generation of reverberation processors has been developed. They apply room impulse responses (RIR) measured in real concert halls and thus guarantee naturalness and authenticity of reverberation. Extending this approach to the use of higher-order spherical microphone arrays provides the means for analyzing the spatiotemporal distribution of acoustic energy. This space-time-frequency representation of the acoustic wave field is also referred to as directional room impulse responses (DRIR) in literature. The objective of the presented work is to develop a perceptually motivated signal-processing environment based on the analysis and re-synthesis of DRIRs. It first extracts perceptual features from measured DRIRs (e.g. source presence and listener envelopment) and thus provides a perceptual signature of the measured room. The room acoustic behavior can then be modified along the various perceptual dimensions, preserving the microstructure of the original RIRs, before being re-synthesized for the use with reverberation processors.

Evaluation of differences in perceived overall acoustical quality and listener envelopment from binaural recordings in a 900-seat hall

Impulse response measurements and binaural recordings were taken in a 900-seat multi-purpose hall in three clusters of nine adjacent seats. Each cluster contained a central seat, the seats immediately to the left and to the right, and the three seats in the rows directly in front of and behind the central seat. Differences between the seats were analyzed in terms of the standard room measures and spatial measures lateral energy fraction (LF) and late lateral energy level (GLL). The typical JNDs were used to evaluate the differences between seat pairs within a given cluster. Differences on the order of 1 or more JNDs were found between most seat pairs within a cluster in most octave bands between 125 Hz to 4000 Hz for early decay time, clarity index, strength, and LF. In terms of GLL, the average difference between pairs of seats was 0.6 dB. However, a total of 14 pairs of seats had differences in GLL between 1.0 to 2.0 dB. A listening test was carried out to determine if subjects could hear differences in the binaural recordings in terms of the listener envelopment and overall acoustical quality. The measurement and subjective test data will be presented.

Improvement of the Acoustics under the Balcony in Auditoria Using the Electro-Acoustic Method—A Study with a Full-Scale Model

In auditoria, the acoustical properties of audience areas located under balconies are regarded as inferior to the main area. This is caused by the reduction of direct and reflected sound energy due to the smaller open area and the reduction of diffusive energy due to the limited acoustical space. In this paper, a new electro-acoustic system is proposed to compensate for this acoustical condition. The proposed system is a non-regenerative system and consists of directional microphones, head amps, a convolver, a matrix processor, amplifiers, and ceiling loudspeakers located under the balcony. The loudspeakers, located at positions corresponding to measurement points across the balcony, recreate the reflecting sound from above the balcony area, which otherwise fail to reach to the listeners under the balcony. The authors have examined the proposed system's performance via two methods: acoustical measurement using a full-scale model and a corresponding psycho-acoustical experiment. The results showed that the energy of the reflections from above the system was the same or more than that without the balcony, and the decay curve with the system was almost the same as that without the balcony. The MUSHRA method was used in the psycho-acoustical experiment, which focused on the evaluation of apparent source width (ASW) and listener envelopment (LEV). The results of the experiment show that the system is significantly better for all tests to the use of no system and that the system is superior to a standerd PA (delay system).

The effect of listener head movement on perceived envelopment and apparent source width

Current research examining listeners' perceived spatial impression of a concert hall relies on a fixed-head worldview, since the overwhelming majority of listening tests conducted to determine subjective spaciousness [listener envelopment (LEV) and apparent source width (ASW)] has required listeners to keep their heads fixed. Such a worldview is an incomplete one, because listeners make noticeable exploratory head movements while evaluating sonic environments, including the more common task of source localization as well as the more involved task of evaluating the spaciousness of a concert hall. This study investigates the role of listener head movement in the evaluation of perceived LEV and ASW under 15 different concert hall conditions simulated over eight loudspeakers using Virtual Microphone Control. The conditions consist of both varying ratios of front-to-back energy and varying levels of cross-correlated reverberant energy. Head movements are monitored in terms of angular rotation (azimuth, elevation, and roll) using a head tracker while listeners are prompted to give subjective ratings of LEV and ASW ranging from 1 (least) to 7 (most). The listening tests are then repeated while subjects are asked to keep their heads fixed. The head movements are analyzed and results of the tests are compared.

Applications of a binaural model with contralateral inhibition in room acoustics analysis

In many cases the conventional, monophonic measures used in analyzing room acoustics show little agreement with real listeners' responses; a binaural perspective provides much-needed spatial and perceptual information that is important in acoustical quality judgments. Traditionally, binaural models extracted information about location and intensity of sound through a relatively simple cross-correlation procedure. This paradigm was extended by Lindemann [J. Acoust. Soc. Am. 80, 1608–1630 (1986)] with the introduction of a contralateral inhibition process, which applies a time- and intensity-dependent weighting to a pair of binaural signals and accurately reproduces results from psychoacoustical tests where the traditional model fails, such as in the case of the Precedence effect. The model will be used to observe the broadening and splitting of auditory events based on the degree of interaural coherence, providing further validation of its adequacy. Then, applications in architectural acoustics will be investigated by processing binaural room impulse responses and producing a binaural activity pattern, which indicates the location and spatial extent of the resulting auditory events. These will be compared to visualizations drawn from spherical harmonic microphones. Implications of such a model on factors important in acoustical quality assessments, such as apparent source width and listener envelopment, will be discussed.

Experiment Research on Apparent Source Width (ASW)

It is well-know that spatial impression is one of the important characteristics in concert halls. It is popular belief that early sound contribute to apparent source width (ASW) and late sound contribute to listener envelopment (LEV). The major concern of our study originated from the question of whether or not ASW was created only by early lateral sound energy alone. In this paper, a group of psychological experiments are performed with simulated sound fields. In the experiment, listening tests were carried out in order to exam the effect of early lateral sound energy fraction(LFE) and early to late sound energy ratio (C80) on perceived ASW. The results confirmed that C80 affects ASW.

The sound strength parameter G and its importance in evaluating and planning the acoustics of halls for music

The parameter, "Strength of Sound G" is closely related to loudness. Its magnitude is dependent, inversely, on the total sound absorption in a room. By comparison, the reverberation time (RT) is both inversely related to the total sound absorption in a hall and directly related to its cubic volume. Hence, G and RT in combination are vital in planning the acoustics of a concert hall. A newly proposed "Bass Index" is related to the loudness of the bass sound and equals the value of G at 125 Hz in decibels minus its value at mid-frequencies. Listener envelopment (LEV) is shown for most halls to be directly related to the mid-frequency value of G. The broadening of sound, i.e., apparent source width (ASW) is given by degree of source broadening (DSB) which is determined from the combined effect of early lateral reflections as measured by binaural quality index (BQI) and strength G. The optimum values and limits of these parameters are discussed.

Sound strength parameter G in concert hall design.

The parameter “Strength of Sound G” is closely related to loudness. Its magnitude is dependent, inversely, on the total sound absorption in a room. By comparison, the reverberation time (RT) is both inversely related to the total sound absorption in a hall and directly related to its cubic volume. Hence, G and RT in combination are vital in planning the acoustics of a concert hall. A newly proposed “bass index” is directly related to the loudness of the bass sound and equals the value of G at 125 Hz minus its value at mid‐frequencies. Listener envelopment (LEV) is shown for most halls to be directly related to the mid‐frequency value of G. The broadening of sound, i.e., apparent source width (ASW), is given by effective spatial impression (ESI) which is determined from the combined effect of early lateral reflections and strength G. The importance of considering G when planning the acoustics of concert halls is emphasized.