Tapio Lokki

Aalto University · Department of Information and Communications Engineering

One of the main factors that makes listening to live concerts emotionally engaging is the dynamic changes in the music. Recent research has shown that concert hall acoustics can affect the perception of orchestral dynamics, but hardly any listening tests have focused on this interplay between the dynamics in music and hall acoustics. In this study,...

This article presents a listening experiment in which the listeners' task was to recognize the acoustics of a seat in a specific concert hall. Stimuli included two short passages extracted from a Beethoven symphony and samples of a solo violin auralized to four real concert halls. In each trial, listeners were presented with a reference and four al...

Sound-absorbing materials are usually measured in a reverberation chamber (diffuse field condition) or in an impedance tube (normal sound incidence). In this paper, we show how angle-dependent absorption coefficients could be measured in a factory-type setting. The results confirm that the materials have different attenuation behavior to sound wave...

Objective: Speech-in-noise tests are widely used in hearing diagnostics but typically without reverberation, although reverberation is an inextricable part of everyday listening conditions. To support the development of more real-life-like test paradigms, the objective of this study was to explore how spatially reproduced reverberation affects spe...

In virtual acoustics, it is common to simulate the early part of a Room Impulse Response using approaches from geometrical acous-tics and the late part using Feedback Delay Networks (FDNs). In order to transition from the early to the late part, it is useful to slowly fade-in the FDN response. We propose two methods to control the fade-in, one base...

The seat-dip effect (SDE) occurs when low-frequency sounds propagate through the seating area of a performance space. The physical aspects governing the effect still puzzle acousticians mostly due to the large variety of seating configurations. In this study, the SDE is investigated in three parameterized hall models using the finite-difference tim...

The present work focuses on how the landscape and distance between a bird and an audio recording unit affect automatic species identification. Moreover, it is shown that automatic species identification can be improved by taking into account the effects of landscape and distance. The proposed method uses measurements of impulse responses between th...

This study investigates the room acoustics of seven chamber music halls of various modern and historical architecture by means of objective room acoustic measures and a subjective listening experiment. The acoustic measurements were performed with heavy cloth covering the audience areas to simulate occupancy in the halls. A loudspeaker quartet was...

Building materials that are bio-based and produced from waste streams have a substantial effect on the carbon footprint of buildings. In this study, the authors prepared fully bio-based sound absorbers from waste wood and other cellulosic materials. Cutter shavings (CSs), softwood pulp, and cellulose powder (CP) were used as raw materials to prepar...

Noise reduction remains an important priority in the modern society, in particular, for urban areas and highly populated cities. Insulation of buildings and transport systems such as cars, trains and airplanes has accelerated the need to develop advanced materials. Various porous materials, such as commercially available foams and granular and fibr...

The spatial decomposition method (SDM) is a parametric approach for the processing of spatial room impulse responses. Although extensively used, there are some issues related to used microphone array, reproduction loudspeaker setup, and signal processing that are not widely understood. For example, there have been different observations with regard...

Acoustic behaviour of wood fibres depends on material properties on different hierarchical structural levels , including molecular, microscopic, and macroscopic. In this paper, we present comprehensive studies on the effect of the hierarchical structure of wood pulp fibres on acoustical properties. In the molecular level, structural polymers of woo...

Room acoustic simulations using the finite-difference time-domain method on a wide frequency range can be computationally expensive and typically contain numerical dispersion. Numerical dispersion can be audible and, thus, constitutes an artifact in auralizations. There is a need to measure perceptual thresholds for numerical dispersion to achieve...

In order to produce high fidelity representations of sound-fields in spatial audio applications, the acoustical nuances occurring within physicals spaces must be included. This includes the effects of scattering from the boundary surfaces of enclosed spaces, as well as the scattering from finite bodies within spaces. Recently, a method has been pro...

Novel and more sustainable sound absorbing materials are produced through the valorization of waste biomass sources by following circular economy principles. Cellulosic nanocrystals (CNC) were extracted from Posidonia oceanica dead leaves, spent barely grains, and kale stems (KS) using a simplified purification protocol. These nanocrystals are used...

This work investigates and evaluates the capabilities of an explicit finite-difference time-domain (FDTD), a fast multipole indirect boundary element method (FMBEM), and a ray acoustic solver in the context of room acoustic modeling and simulations. In room acoustic simulations, the wave-based FDTD and FMBEM methods are known for generating accurat...

A method for representing acoustic scattering in the Spherical Harmonic domain is applied to simulated responses of a non-diffusive and a diffusive geometry. Established metrics are applied in order to evaluate the performance of these geometries and their effects are traced to the Spherical Harmonic domain. The analysis of the scattering geometry...

A common aim in virtual reality room acoustics simulation is accurate listener position dependent rendering. However, it is unclear whether a mismatch between the acoustics and visual representation of a room influences the experience or is even noticeable. Here, we ask if listeners without any special experience in echolocation are able to identif...

The spatial speech reproduction capabilities of a KEMAR mouth simulator, a loudspeaker, the piston on the sphere model, and a circular harmonic fitting are evaluated in the near-field. The speech directivity of 24 human subjects, both male and female, is measured using a semicircular microphone array with a radius of 36.5 cm in the horizontal plane...

This article proposes a parametric signal-dependent method for the task of encoding microphone array signals into Ambisonic signals. The proposed method is presented and evaluated in the context of encoding a simulated seven-sensor microphone array, which is mounted on an augmented reality headset device. Given the inherent flexibility of the Ambis...

For the evaluation of virtual acoustics for mixed realities, we distinguish between the paradigms 'authenticity', 'plausibility' and 'transfer-plausibility'. In the case of authenticity, discrimination tasks between real sound sources and virtual renderings presented over headphones are performed, whereas in case of a plausibility experiment, liste...

Compared to geometrical acoustics, wave-based methods which solve the wave equation either in the time domain or in the frequency domain are known for their high accuracy. However, their systematic use as professional room acoustic simulation tools is less popular due to the modelling effort and computational time requirements, especially in the ca...

Multichannel auralizations based on spatial room impulse responses often employ sample-wise assignment of an omnidirectional response to form loudspeaker responses. This leads to sparse impulse responses in each reproduction loudspeaker and the auralization of transient signals can sound rough. Based on this observation, we conducted a listening te...

Ambisonic recording with spherical microphone arrays (SMAs) is based on a far-field assumption which determines how microphone signals are encoded into Ambisonic signals. In the presence of a near-field source, low-frequency distance-dependent boosts arise in SMAs in similar nature to proximity effects in far-field equalized directional microphones...

A method is proposed to encode the acoustic scattering of objects for virtual acoustic applications through a multiple-input and multiple-output framework. The scattering is encoded as a matrix in the spherical harmonic domain, and can be re-used and manipulated (rotated, scaled and translated) to synthesize various sound scenes. The proposed metho...

Several parametric spatial room impulse response rendering methods use broadband directional estimates, whereby based on sample-by-sample direction-of-arrival estimation, a single channel room impulse response is distributed to multiple loudspeakers. To this end, it has been unclear how such simple parametric processing behaves in the late part of...

In this study, sound absorbing materials were produced through foam forming technique using hardwood and softwood pulps with varying chemical composition, ultrastructural, and morphological properties as raw materials. The sound absorption properties of the produced foams were measured and related to the ultrastructure and the morphology of the pul...

Acoustic comfort is directly related to enhanced well-being and performance of people. A typical challenge faced by architects and acousticians is to achieve adequate acoustics while maintaining the aesthetics of the space and reducing the visual aspects of acoustic materials and elements. In this study, we present a biofiber-based acoustic coating...

Measured spatial room impulse responses have been used to compare acoustic spaces. One way to analyze and render such responses is to apply parametric methods, yet those methods have been bound to single measurement locations. This paper introduces a method that locates image sources from spatial room impulse responses measured at multiple source a...

The relationship between perceived pitch and harmonic spectrum in complex tones is ambiguous. In this study, 31 professional orchestra musicians participated in a listening experiment where they adjusted the pitch of complex low-register successively presented tones to unison. Tones ranged from A0 to A2 (27.6–110 Hz) and were derived from acoustic...

This paper presents a perceptual evaluation of numerical dispersion in free-field headphone-based head-tracked binaural auralizations of finite difference time domain (FDTD) simulations. The simulated pressure, captured by virtual volumetric receiver arrays, is used to perform a spherical harmonics decomposition of the sound field and generate bina...

The low-frequency attenuation in the direct sound due to the concert hall seats, i.e., the seat-dip effect, is studied with the help of a scale model comprising an adjustable seating area and an enclosed box. More particularly, different seat underpass sizes and floor raking angles are studied, and the results are averaged over multiple source posi...

This chapter discusses the acoustics of concert halls from the viewpoint of binaural perception. It explains how early reflections have a crucial role in the quality of sound, perceived dynamics, and timbre. In particular, the directions from which these reflections reach the listener are important for human spatial hearing. The chapter has strong...

One of the central acoustical features of a concert hall is its ability to make sound sufficiently loud. Acoustics researchers often measure the objective parameter strength to investigate sound-amplifying properties of a hall. However, the strength is a linear variable, it does not reveal anything about the true dynamic responsiveness of a hall. T...

An experiment was conducted to identify the perceptual effects of acoustical properties of domestic listening environments, in a stereophonic reproduction scenario. Nine sound fields, originating from four rooms, were captured and spatially reproduced over a three-dimensional loudspeaker array. A panel of ten expert assessors identified and quantif...

In a musical performance, musician, instrument and room form a closed feedback loop that continuously shapes the generated sound. A virtual acoustic environment was developed to study performance adjustments systematically. In formal experiments, 11 trumpet players were recorded while performing several pieces with multiple auralized versions of re...

The reverberation of a room is often controlled by installing sound absorption panels to the ceiling and on the walls. The reduced reverberation is particularly important in classrooms to maximize the speech intelligibility and in open-plan offices to make spaces more pleasant. In this study, the impact of the placement of the absorption material i...

This paper presents an investigation of the effects of relatively large-scale pyramidal and convex-shaped diffusers on the acoustical properties of a small non-diffuse rectangular room. Room impulse responses (RIRs) were measured in various room configurations to extract the early decay time (EDT), reverberation time (T20), early-to-late arriving s...

The purpose of this paper is to spark discussions on the recent trends of designing vineyard and surround-type concert halls. We understand that these halls could be architecturally unique and many conductors like them, however, as outlined in this paper, they do not always serve the best for music acoustically. The motivation for visual proximity...

This paper presents a method to determine if differences between the scattering created by geometrically-similar diffuser designs are perceivable. Although there exist standards to measure the scattering and diffusion coefficients, the perceptual evaluation of the scattering created by diffusing surfaces has previously been scarcely examined. In th...

This study case explores a novel personal listening device in the context of spatial audio which, in normal use, is located behind the listener's head. Several techniques were applied to binaural signals with the intention of rendering spatial sound in front of the listener. Implementations of binaural, ipsilateral compensation, crosstalk cancellat...

Sensory Evaluation of Sound provides a detailed review of the latest sensory evaluation techniques, specifically applied to the evaluation of sound and audio. This three-part book commences with an introduction to the fundamental role of sound and hearing, which is followed by an overview of sensory evaluation methods and associated univariate and...

Direct-to-reverberant ratio threshold for localization was studied with anechoic orchestra instrument recordings in auralized concert halls. Excerpts of anechoic music were convolved with spatial impulse responses and reproduced with a multichannel loudspeaker system in anechoic chamber. Participants adjusted direct sound level in order to explore...

Spherical microphones arrays are commonly utilized for recording, analyzing and reproducing sound-fields. In the context of higher-order Ambisonics, the spatial resolution depends on the number and distribution of sensors over the surface of a sphere. Commercially available arrays have set configurations that cannot be changed, which limits their u...

The seat-dip effect is a collection of phenomena attributable to sound waves diffracting from the tops of the seat backs, and reflecting between the seats that form a regular structure comparable to the wavelength of the low end of audible frequency range. The audience becomes a part of that structure when seated. Thus far, most measurements on the...

Higher-order Ambisonics (HOA) is a flexible recording and reproduction method, which makes it attractive for several applications in virtual and augmented reality. However, the recording of HOA signals with practical compact microphone arrays is limited to a certain frequency range, which depends on the applied microphone array. In this paper, w...

Sound and music computing is a young and highly multidisciplinary research field. It combines scientific, technological, and artistic methods to produce, model, and understand audio and sonic arts with the help of computers. Sound and music computing borrows methods, for example, from computer science, electrical engineering, mathematics, musicolog...

The use of headphones in reproducing spatial sound is becoming more and more popular. For instance, virtual reality applications often use head-tracking to keep the binaurally reproduced auditory environment stable and to improve externalization. Here, we study one spatial sound reproduction method over headphones, in particular the positioning of...

Acoustical conditions on stage have an influence on the sound and character of a musical performance. Musicians constantly adjust their playing to accommodate to the stage acoustics. The study of acoustical preferences of musicians is part of the characterization of this feedback loop, which impacts on the musicians' comfort as well as on the aural...

Many people are exposed to large sound pressure levels either occasionally or regularly, and thus need to protect their hearing in order to prevent hearing loss and other hearing disorders. Earplugs are effective at attenuating sound from the environment, but they do not attenuate bone-conducted sound, but instead amplify it at low frequencies due...

Dynamic responsiveness is an important feature in room acoustics for making music more enjoyable. The concert hall should render the most silent pianissimos audible everywhere, including the last row, yet support fully the loudest fortissimos. The realization of these effects is impossible to objectively quantify by analyzing solely the measured im...

In concert halls, the spectrum of direct sound (here 0 to 15 ms) is influenced by the seat-dip effect that causes selective low frequency attenuation. The seat-dip effect has been considered to be detrimental to the acoustic quality of halls, yet there is little evidence about the perceptual significance of the effect. This paper studies the discri...

More than a hundred years of research on concert hall acoustics has provided an extensive list of attributes to describe and evaluate the perceptual aspects of sound in concert halls. This brief overview discusses the current knowledge, and presents a " wheel of concert hall acoustics " in which the main aspects are gathered together with the descr...

An experiment was conducted to determine the perceptual effects of car cabin acoustics on the reproduced sound field. In-car measurements were conducted whilst the cabin's interior was physically modified. The captured sound fields were recreated in the laboratory using a three-dimensional loudspeaker array. A panel of expert assessors followed a r...

Multivariate paired comparisons allow one to compare stimuli by pairs on more than one situation (different contexts, several types of preferences or various sensory attributes). This paper focuses on the segmentation of the subjects after such a task. An adaptation of the latent class segmentation, based on the Bradley-Terry-Luce model, to the mul...

Concert hall acoustics have been traditionally evaluated by means of room acoustic measurements and perceptual studies, which requires an available concert hall, orchestra, and audience. This article presents a physical and perceptual comparison of room acoustics between arrays of real loudspeakers and virtual loudspeakers implemented with Wave Fie...

Concert hall acoustics is a multidisciplinary research topic, although often people think that it is only measuring and analysing impulse responses. This paper goes beyond the room impulse responses and explains in particular the features of sound sources and listeners in a concert hall. In addition, the paper collects the recent research results o...

Dynamics is one of the principal means of expressivity in Western classical music. Still, preceding research on room acoustics has mostly neglected the contribution of music dynamics to the acoustic perception. This study investigates how the different concert hall acoustics influence the perception of varying music dynamics. An anechoic orchestra...

Previous studies on musicians' adjustments to room acoustics have demonstrated an influence of room acoustics on live solo music performance. Musicians adjust different aspects of the performance, such as tempo, articulation, dynamics or level. However, this effect seems to be highly dependent on individual musicians, musical pieces and instruments...

This paper focuses on the analysis of measurements in a Finnish opera house with respect to the seat-dip effect. The effect features an attenuation of low frequencies due to sound waves arriving at small incidence angles to the tops of the seat backrests and bending between seats before interfering destructively with the direct sound at the listene...

Some studies of concert hall acoustics consider the acoustics in a hall as a single entity. Here, it is shown that the acoustics vary between different seats, and the choice of music also influences the perceived acoustics. The presented study compared the acoustics of six unoccupied concert halls with extensive listening tests, applying two differ...

Most studies on the influence of the direction of late reverberation on listener envelopment (LEV) in concert halls have been conducted in laboratory conditions, i.e. where synthetic sound fields and a relatively limited number of loudspeakers were used to approximate a real, spatially quite complex acoustic situation. This study approaches LEV fro...

Since 2009, we have now completed three individual vocabulary profiling studies of auralized concert hall acoustics. I