Late Reflections Research Articles

Where not to install a reverberation enhancement system

For hundreds (perhaps thousands) of years venues for live performance emphasized communication—the transfer of speech or musical information from performers to listeners—as paramount to success. The Greeks could perform drama to 15,000 listeners without microphones, and halls used by Haydn, Mozart, and Beethoven were small and dry. Wagner built a fan-shaped opera hall with an absorbent stage, a covered pit, and no lateral reflections. It is still considered perhaps the best in the world. Sabine and others made lecture and Vaudeville halls that worked. But in the 20th century suddenly early reflections were essential, and long reverberation times desirable. Wood stages and lateral reflections were mandatory. These ideas linger on. In this talk we share our experiences of often misguided attempts to improve sound in venues of all types. The lessons we learned from a few perceptive musicians and artists have changed our approach to acoustics. Attention is the key, not reverberation. Reverberation can be lovely if it enhances a listening experience, but it must not muddle the performance. There are ways to get it right, but doing so requires the right system, careful adjustment, and close attention to the natural acoustics of the venue.

Inter-aural cross-correlation measured during symphony orchestra performance in big concert halls

Spatial impression in concert hall listeners is known to depend on lateral reflections causing differences between the sound at the left ear and the right ear. Such differences can be measured, e.g., by the so-called inter-aural cross-correlation IACC in a binaural signal pair, i.e., a signal pair from microphones placed in the ear canal entrances. IACC data from binaural impulse responses (BRIR) are commonly reported. In contrast, little attention has been paid to running IACC, i.e. IACC(t), during music performance. Therefore, in 2011 this author launched the Binaural Project in 2011 in order to collect binaural signal data from concerts with symphony orchestras. An analysis of IACC(t) from more than 600 minutes of binaural recordings during concerts in many big concert halls is presented. Several famous halls, including Boston Symphony Hall, are included in the data. Among the questions to be answered are Can we observe from the data that concert halls make a difference to IACC(t)? If so—is this variation small or big compared to the variation from one moment to another, bar to bar, movement to movement, from one orchestra to another, and so on? On the other hand, if we cannot observe significant hall-to-hall differences, several new questions would arise, including How can we maintain that listeners are able to perceive hall-to-hall differences in ASW and LEV? And why do not the reported hall-to-hall differences in IACC from impulse responses (ISO-3382) make an observable difference to running IACC(t)?

Modification of the head-related transfer functions for auditory proximity in rooms

The human hearing uses two signals entering the ears to interpret surrounding spaces and sound sources, and certain acoustic impressions are often regarded favorably by the listeners. At times, music consumers may consider auditory proximity and intimacy as a desired sensation. In some scenarios, the acoustic reflections, often arriving from lateral angles, succeed in enhancing the perceived proximity, even though all acoustic events occur at far distances. In contrast, natural sounds emanating from a very close proximity are instinctively perceived as intimate. The perception of spatial sound is based on the binaural cues, which can be modeled with head-related transfer functions (HRTF). Earlier research has demonstrated that the interaural level difference for lateral incidence is the foremost difference between near and far-distance HRTFs. In the context of room acoustics, only lateral reflections arrive from angles which at high frequencies create traces of interaural level difference otherwise characteristic to near-field HRTF. This paper explores altering the auditory proximity of auralizations by introducing near-field-type interaural level differences to widely available far-field HRTFs. Analysis of the application of these modified HRTF to reflected sound provides more insight into the sources of auditory proximity.

How accurate dereverberation should be? Effects of underestimating and overestimating binaural room impulse responses

The sound arriving at the listeners' ears is influenced by the binaural room impulse response (BRIR) of the listening environment. Previous research (Srinivasan et al., 2017) has suggested that removing late reflections in BRIR improves speech understanding most when spatial cues are absent. However, in real world listening scenarios, it is difficult to differentiate between the effects of early reflections and late reverberation. Here, we present data from an experiment evaluating the effects of a simple static dereverberation technique on speech understanding for two reverberant environments (T60 = 1 and 2 s). The input speech signal was dereverbered by deconvolving the speech signal under three different conditions: (1) underestimating the effects of reverberation, (2) overestimating the effects of reverberation, and (3) correct estimation of the effects of reverberation. Effects of the three deconvolving techniques on identification thresholds and amount of release from masking will be discussed.

Dependence of Photoelectrochemical Properties on Geometry Factors of ZnO Nanostructured Networks

The recent surge of alternative clean energy with minimal environmental impact in a cost-effective way requires the exploration of new materials and/or structures as efficient electrodes for industry-level photoelectrochemical (PEC) water splitting into usable H2 fuel. It is well-known that nanomaterials could outperform their bulk counterparts in many aspects because of increased interacting sites, shorter lateral diffusion distance and lower reflectivity. Assembling nano-building blocks into desirable structures is a more advanced intelligent tactic for realizing higher performance and better functionality by exploiting new hierarchy and scaling-up laws. To meet the challenges, hierarchical 3-D nanostructures integrating 1-D conduction trunks and secondary branches, e.g. dendritic nanowires (NWs)/nanofibers (NFs), are particularly desired in light of the greatly improved light-harvesting, the efficient charge separation and short hole diffusion length (L D) for which the refined secondary structures are responsible. In terms of methodology, a seeding method in solution phase still confronts some engineering obstacles notwithstanding it being regarded as a major avenue to fabricate heterogeneous nanostructures of semiconductors. To elevate the spatial occupancy of one-dimensional ZnO nanostructures and overcome the limitations of multistep seeding method currently widely used, a rational, facile and high-yielding procedure will be presented here for the fabrication of the interconnected three-dimensional “caterpillar-like” ZnO nanostructured networks (CZNs) for photoelectrochemical applications. Moreover, by fine-tuning the synthesis procedure and manipulating their growth process, the dependence of their photoelectrochemical properties on geometry factors of these unique CZNs consisting of branched ZnO nanowires onto ZnO nanofibers with tunable surface-to-volume ratio and roughness factor has been investigated. They offer mechanically and electrically robust interconnected networks with open micrometer-scale structures and short hole diffusion length. The preferential light-material interaction and charge separation to maximize the photo-to-hydrogen conversion efficiency were further studied. When used as photoanode, our CZNs not only favor sunlight harvesting with multireflection ability, but also suppress the recombination of photogenerated charge. Compared to the literature results, our CZN photoanodes with ZnO nanobranches of ~2.2 μm in length and ~25 nm in diameter exhibited the highest photocurrent density of 0.72 mA∙cm-2 at +1.2 V (versus Ag/AgCl) and conversion efficiency of 0.209% at +0.91 V (versus RHE) without being decorated with noble metal cocatalysts or nonmetallic/metallic dopants due to their favorable structural features. Overall, our procedure to obtain the desirable CZN provides great opportunities for facile and efficient fabrication of model photoelectrochemical anodes and would be applied to other materials for sustainable chemistry and engineering applications.

Effect of a chamber orchestra on direct sound and early reflections for performers on stage: A boundary element method study.

Early reflections are known to be important to musicians performing on stage, but acoustic measurements are usually made on empty stages. This work investigates how a chamber orchestra setup on stage affects early reflections from the stage enclosure. A boundary element method (BEM) model of a chamber orchestra is validated against full scale measurements with seated and standing subjects in an anechoic chamber and against auditorium measurements, demonstrating that the BEM simulation gives realistic results. Using the validated BEM model, an investigation of how a chamber orchestra attenuates and scatters both the direct sound and the first-order reflections is presented for two different sized "shoe-box" stage enclosures. The first-order reflections from the stage are investigated individually: at and above the 250 Hz band, horizontal reflections from stage walls are attenuated to varying degrees, while the ceiling reflection is relatively unaffected. Considering the overall effect of the chamber orchestra on the direct sound and first-order reflections, differences of 2-5 dB occur in the 1000 Hz octave band when the ceiling reflection is excluded (slightly reduced when including the unobstructed ceiling reflection). A tilted side wall case showed the orchestra has a reduced effect with a small elevation of the lateral reflections.

The role of early and late reflections on spatial release from masking: Effects of age and hearing loss.

Early reflections have been linked to improved speech intelligibility, while later-arriving reverberant sound has been shown to limit speech understanding. Here, these effects were examined by artificially removing either early reflections or late reflections. Removing late reflections improved performance more for colocated than for spatially separated maskers. Results of a multiple regression analysis suggest that pure-tone average (PTA) is a significant predictor of spatial release from masking (SRM) in all acoustic conditions. Controlling for the effects of PTA, age is a significant predictor of SRM only when early reflections are absent.

Interactive sound propagation with bidirectional path tracing

We introduce Bidirectional Sound Transport (BST) , a new algorithm that simulates sound propagation by bidirectional path tracing using multiple importance sampling. Our approach can handle multiple sources in large virtual environments with complex occlusion, and can produce plausible acoustic effects at an interactive rate on a desktop PC. We introduce a new metric based on the signal-to-noise ratio (SNR) of the energy response and use this metric to evaluate the performance of ray-tracing-based acoustic simulation methods. Our formulation exploits temporal coherence in terms of using the resulting sample distribution of the previous frame to guide the sample distribution of the current one. We show that our sample redistribution algorithm converges and better balances between early and late reflections. We evaluate our approach on different benchmarks and demonstrate significant speedup over prior geometric acoustic algorithms.

Electronic shell―Improvement of room acoustics without orchestra shell utilizing active field control

This paper introduces an example of Electronic Shell acoustic enhancement system that was installed in a multi-purpose hall without an orchestra shell. The system is based on the concept of Active Field Control using electro-acoustic means. The three objectives of this system were 1) the enhancement of early reflection for performers, 2) the extension of the reverberation time and the enhancement of the total sound energy on stage, and 3) the enhancement of early reflection in the audience area. The application of this system showed an improvement of about 1 to 2 dB in STearly and more than 2 dB in G in the audience area, which is equivalent or better performance than simple mobile type orchestra shell. Regarding the spatial sound structure and the time domain characteristics between simple mobile type shell and the Electronic Shell system, there are differences since the mobile type shell mainly takes care of lateral reflections; on the other hand, the Electronic Shell system takes care of overhead reflections, and it cannot provide some early reflections after the direct sound arrives. It was clarified the relationship between the differences in physical features and the subjective improvement of the musical performance using a temporal system installed in a rehearsal hall.

A speech pre-processing method to reduce overlap masking in reverberant environments

In daily life, we are often exposed to speech that is rendered over loudspeakers in a reverberant acoustical environment (examples are public-address systems used in a train station or conference halls). Whereas the early reflections can support speech intelligibility, the late reflections smear the speech in time which will result in an overlap of consecutive speech portions and an effective low-pass filtering of the speech-specific modulation spectrum. This study proposes a perceptually motivated pre-processing approach, based on previous work of Hodoshima et al. [J. Acoust. Soc. 119, 4055-4064 (2006)], which reduces the detrimental effects of reverberation by suppressing steady-state portions and emphasizing potentially inaudible/masked segments of speech before it is emitted in the reverberant environment. For pre-processing, the impulse response is separated into a direct and a reverberant path to decide whether speech segments are inaudible and can be neglected or should be emphasized. A speech intelligibility prediction model is used to select the optimal pre-processing parameters for each specific acoustical environment. Listening tests showed, that this pre-processing approach is able to partially compensate the detrimental effects of reverberation leading to a reduction in speech reception thresholds of about 2 to 5 dB measured in speech shaped noise.

An Expectation-Maximization Algorithm for Multimicrophone Speech Dereverberation and Noise Reduction With Coherence Matrix Estimation

In speech communication systems, the microphone signals are degraded by reverberation and ambient noise. The reverberant speech can be separated into two components, namely, an early speech component that consists of the direct path and some early reflections and a late reverberant component that consists of all late reflections. In this paper, a novel algorithm to simultaneously suppress early reflections, late reverberation, and ambient noise is presented. The expectation-maximization (EM) algorithm is used to estimate the signals and spatial parameters of the early speech component and the late reverberation components. As a result, a spatially filtered version of the early speech component is estimated in the E-step. The power spectral density (PSD) of the anechoic speech, the relative early transfer functions, and the PSD matrix of the late reverberation are estimated in the M-step of the EM algorithm. The algorithm is evaluated using real room impulse response recorded in our acoustic lab with a reverberation time set to 0.36 s and 0.61 s and several signal-to-noise ratio levels. It is shown that significant improvement is obtained and that the proposed algorithm outperforms baseline single-channel and multichannel dereverberation algorithms, as well as a state-of-the-art multichannel dereverberation algorithm.

Seismo-stratigraphic evidences for deep base level control on middle to late Pleistocene drift evolution and mass wasting along southern Levant continental slope (Eastern Mediterranean)

Since early Pliocene, a counterclockwise surface gyre transported Nile derived silt and clay northeastwards along the Levant coast, where a basinward prograding plastered drift emerged. Based on high-resolution seismic reflection data we develop a middle to late Pleistocene sequence stratigraphic scheme for this plastered drift. For creating stacked sections of the seismic data we used the common reflection surface (CRS) stack technology which enhanced lateral reflection continuity and visibility of deep reflections. The shelf comprises stratigraphic sequences which show classical, systems tract like stacking patterns of sea level controlled sequences such as offlapping forced regression deposits or diachronous ravinement surfaces which formed during base level rise. On the slope, base level was periodically located well below the wave base and thus rather controlled by hydrodynamics, presumably by high-velocity contour currents. Hence, the term ‘deep base level’ is introduced. The deep base level controlled especially down and backstepping slope deposits. This example shows that care has to be taken when interpreting subsurface data containing typical systems tract like seismic sequences, since such geometries do not necessarily imply shallow water deposition of the sediments. A chronostratigraphic analysis based on the seismic stratigraphy indicates that base level fluctuations were related to eccentricity driven glacio-eustatic fluctuations. Periodic mass wasting, facilitated by foreset over-steepening and possibly triggered by salt tectonics or erosion by the contour current occurred during late base level fall or early base level rise.

Anomalous phenomena on HF radio paths during geomagnetic disturbances

We analyze ionospheric oblique sounding data on three high-latitude and one high-latitude–midlatitude HF radio paths for February 15 and 16, 2014, when two substorms and one magnetic storm occurred. We investigate cases of anomalous propagation of signals: their reflection from sporadic layer Es, lateral reflections, type “M” or “N” modes, the presence of traveling ionospheric disturbances, and the diffusivity of signals and triplets. The most significant results are the following. In geomagnetically undisturbed times, sporadic Es-layers with reduced maximum observed frequencies (MOFEs) on three high-latitude paths were observed in both days. The values of MOFEs during disturbances are large, which leads to the screening of other oblique sounding signals reflected from the ionosphere. On all four paths, the most frequently traveling ionospheric disturbances due to the terminator were observed in quiet hours from 03:00 to 15:00 UT on the first day and from 06:00 to 13:00 UT on the second day of the experiment. In addition, both the sunset terminator and the magnetic storm on the high-latitude–mid-latitude path were found to generate traveling ionospheric disturbances jointly. No such phenomenon was found on high-latitude paths.

Area scalable optically induced photorefractive photonic microstructures

A convenient approach to fabricate area scalable two-dimensional photonic microstructures was experimentally demonstrated by multi-face optical wedges. The approach is quite compact and stable without complex optical alignment equipment. Large-area square lattice microstructures are optically induced inside an iron-doped lithium niobate photorefractive crystal. The induced large-area microstructures are analyzed and verified by plane wave guiding, Brillouin-zone spectroscopy, angle-dependent transmission spectrum, and lateral Bragg reflection patterns. The method can be easily extended to generate other more complex area scalable photonic microstructures, such as quasicrystal lattices, by designing the multi-face optical wedge appropriately. The induced area scalable photonic microstructures can be fixed or erased even re-recorded in the photorefractive crystal, which suggests potential applications in micro-nano photonic devices.

En bloc pelvic resection for advanced ovarian cancer preceded by central ligation of vessels supplying the tumor bed: a description of surgical technique and a feasibility study

BackgroundThe resection of all visible malignancies increases the likelihood for long-term survival in epithelial ovarian cancer. The complete extinguishment of pelvic disease is possible using en bloc pelvic resection. The no-touch isolation technique aims to reduce cancer cells flowing from the primary tumor site to the liver and other organs by ligating blood and lymphatic vessels first. objectives are to present the operative details and to establish the feasibility of the modified technique of en bloc pelvic resection, which begins with the central ligation of vessels supplying the tumor bed.MethodsTwenty patients with pelvic tumor extensively infiltrating into adjacent pelvic organs were uniformly operated on. The surgical plan commenced with incisions along the lateral peritoneal reflections immediately medial to the white line of Toldt followed by a retroperitoneal central ligation of ovarian and mesenteric vessels and the ovarian lymphovascular flow. Then, the routine steps of en bloc pelvic resection were performed. Data on treatment were assessed.ResultsIn all cases, no gross residual disease was achieved. The median durations of the surgical procedure and the hospital stay were 320 min (range: 205–430 min) and 12 days (range: 7–44 days), respectively. The complications were as follows: wound infection (n = 1), anastomosis dehiscence (n = 1), total parenteral nutrition (n = 4), and death (n = 1, PE). The median follow-up time period was 19 months (range: 8–31 months). No patient experienced a recurrence of pelvic disease.ConclusionsPerforming a central ligation of vessels supplying the tumor bed prior to an en bloc pelvic resection is feasible with acceptable morbidity and mortality rates.

The role of early and late reflections on spatial release from masking

It is well documented that older listeners have more difficulty understanding speech in complex listening environments than do younger listeners. Early reflections (occurring <50 ms following the direct sound) have been linked to improved speech intelligibility (Lochner and Burger, 1964), while later-arriving reverberant sound has been shown to limit speech understanding (Knudsen, 1929). However, we do not know how spatial release from masking (SRM) is affected by early and late reflections or how age and hearing loss interacts with the relative influences of each. SRM in two simulated reverberant environments was measured for listeners varying in age and hearing thresholds under three different signal processing conditions: (1) early reflections alone, (2) late reflections alone, and (3) all reflections. Results indicated that though all listeners performed better when only early reflections were present, the older hearing-impaired listeners benefited the most from the absence of late reflections. Effects of age and hearing loss on performance and SRM under these three different signal processing conditions will be discussed. [Work supported by NIH R01 DC011828.]

Using individually equalized playback of binaural recordings from an electronic orchestra to determine the effects of early reflections on proximity, localization, and loudness

Reflections in the first 50 ms are often assumed to enhance sound quality, but data supporting the assumption are lacking. We need to know when reflections are beneficial, and when they are not. Work by Lokki et al. may help to answer this question, but we have developed a binaural recording and playback technique that yields as good or better results. The key is individual equalization from the microphone to the eardrum of a listener. We have developed a quick and non-invasive method of headphone equalization that produces accurate timbre and frontal localization without head-tracking. This enables binaural impulse responses from a number of instrument positions in real halls to be manipulated by adding or deleting individual reflections and then evaluated with blind listening tests. Data from Boston Symphony show that early lateral reflections in the front of the hall are typically inaudible, but early medial and lateral reflections in the rear of the hall can reduce or eliminate proximity, clarity, impact, envelopment, and the ability to localize individual instruments. Deleting one or two of the earliest and strongest reflections improves all of those perceptions with no effect on loudness.

Deep history: reflections on the archive and the lifeworld

This paper outlines an approach for comparing Edmund Husserl’s late historical-teleological reflections in the Crisis of the European Sciences with Michel Foucault’s archaeology of discursive formations in his Archaeology of Knowledge, with a particular emphasis on the notion of an “historical apriori.” The argument is that each conception of historical reflection complements the other by opening up a depth dimension that moves beyond the traditional limits of the philosophy of history. In Husserl, the concept of the lifeworld fixes the parameters of a “deep history” as the horizon of anonymous subjective comportment, while in Foucault the concept of the archive delimits an alternative deep history of the anonymous production of discursive formations. Together, Husserl and Foucault represent two important moments of the radicalization of the theme of history in twentieth century philosophy, one seeking to extend the limits of transcendental philosophy, the other contesting the domain of the transcendental altogether.

Proposals and Analysis of the Effects of Acoustic Corrections in a Modern Church

It is rather common experience to observe that many contemporary churches, in contrast with the effort to achieve refined architectonic shapes and finishes, exhibit poor acoustic quality, such as high reverberation times and low speech intelligibility. The causes of such deficiencies are ordinarily generated by the smooth and hard surfaces of walls, floor and ceiling that focus most of sound energy in late reflections, diminishing the effectiveness of direct and early reflected sound. Recently, the authors have been involved for analyzing the acoustic behavior of a modern church situated in Ragusa, (Italy), with the aim to individuate suitable interventions for improving the acoustic quality of that church. Preliminarily, a measurement survey was conducted to evaluate the main acoustic indices proposed by ISO 3382 (T30, STI, EDT, C80, D50) and portray the current acoustic climate. After that, the Authors developed a simulation on a 3D model of the church, in order to calibrate the model comparing measured and simulated acoustic parameters. The previously described activities are necessary for testing the reliability and accuracy of the prediction of the acoustic simulations. The subsequent step of the work consists in the choice of suitable interventions for the acoustic corrections; three different typologies of materials were evaluated. Globally, the acoustic corrections allow to obtain noteworthy improvements of the acoustic quality of the church, e.g. the T30 decrease from 7.3 to 2.5 s and the STI increase from 33% to 40%, at 1000 Hz. Further, the influence of the variation of the audience presence was analyzed, finding out a strict correlation between occupancy percentage and the law of variation of T30. Finally, after the realizations of one of the suggested interventions of acoustic corrections, the Authors conducted a second survey to evaluate the effects of the refurbishment interventions on the acoustic climate. Since the obtained results do not match very well with the design previsions, some hypotheses that can justify such discrepancy are illustrated.

Analysis and Acoustic Correction of a Contemporary Italian Church

Nowadays, architects and designers build new churches primarily considering the architectural shape to emphasize the iconographic message without sufficiently investigating the acoustic climate. In many cases, designers propose elliptical or irregular geometries for the shapes of these buildings and, in addition, the furniture of indoor surfaces have unsuitable absorption and diffusivity coefficients. Thereby, it can be observed the arise of serious acoustical problems such as standing waves, flutter echo, sound focusing and intensive late reflections (greater than 100ms) which seriously decrease speech intelligibility and diminish the effectiveness of the early sound energy. This paper presents the results of an acoustic survey on the Catholic Church “Invaluable Blood of Jesus”, situated in Ragusa (Italy), which is characterized by many problems mentioned above. During last years, some refurbishment interventions have attempted to reduce the acoustic discomfort, but an uncorrected approach has completely compromised the speech intelligibility, especially during liturgical functions. Recently, the authors have been involved to propose suitable interventions for improving the acoustic quality of this environment. Preliminarily, a measurement survey was conducted to evaluate the main acoustic indices (RT60, STI, EDT, C80, D50) and portray the current acoustic climate. After that, it was developed an acoustic computer simulation on a 3D model of the church, in order to calibrate the model comparing measured and simulated data. This procedure allowed testing the reliability and accuracy of the model.Finally, We propose two different interventions of acoustic correction. Globally it is possible to obtain an improvement of RT60 from 7.3 to 2.5 s at 1kHz and STI increases from 33% to 40%, at 1000Hz.