General Acoustics / Underwater Acoustics
Generator curve for the study of diffraction by a spherical signal around a half-plane
In recent work of the authors a solution has been proposed for diffraction by a half-plane in a unified form for all types of incident signals - being exact for plane and approximate for cylindrical and spherical signals. Based on this solution a generator curve for the diffraction has been introduced as a function of a single variable, namely the diffraction number. The diffraction number is a universal diffraction parameter, which translates the generator curve into diffracted signal at all times and all source-receiver locations, according to a condition termed the similarity condition. In the present work, these observations are expanded to the exact solution for the spherical incident signals. The generator curve is the same for the exact solution with a change in the diffraction number. The behavior of the new diffraction number in space and time is investigated and a new similarity condition is introduced. Finally, based on this behavior the diffracted signal is separated in time stages, each one with distinct characteristics.
Piecewise convolution for the closed form solution of diffraction by arbitrary incident signals around half-planes
In the present study diffraction of spherically spreading signals by half-planes is considered. An analytical impulse response solution proposed previously by the authors is investigated. It is shown that its primitive functions exist, can be expressed in a compact form, and when employed instead of the impulse response itself can dramatically reduce the computational cost of the convolution. Furthermore, based on the primitive functions a closed form solution can be obtained for the diffraction signal produced by any continuous incident signal. Finally, the method is extended to handle discontinuous incident signals by employing the closed form solution to segments of the incident signal.
Semi-empirical methods for computing the insertion loss behind an acoustically rigid wedge
The analytical solutions for the diffraction field around a wedge are mathematically complex. Based on an existing approximate analytical solution the insertion loss in the shadow zone behind a wedge is investigated and the following are proposed for fast and easy calculations: (i) an approximate relation as a function of two parameters (and the corresponding database that can be generated), (ii) the corresponding family of curves, and (iii) a semi-empirical relation containing simple mathematical functions. The recommendations are compared against the established Hadden analytical solution, as well as with existing semi-empirical models.
The policy of the European Union as regards the ambient noise in the sea and the QUIETMED project.
The paper summarizes the policy of the European Union to protect the marine environment from underwater noise as reflected in Directive 208/56 / EC known as the Marine Strategy Framework Directive.
According to this directive, the member States will have to ensure Good Environmental Status by 2022.
The European Commission’s QUIETMED program, in which the Foundation for Research and Technology Hellas is participating, aims to develop a uniform methodology among the Mediterranean coastal states for the monitoring and recording of the underwater noise.
The paper describes the objectives of the program and the participation of FORTH in it.
An experiment for recording ambient noise in deep sea.
Under the QUIETMED project, the Underwater Acoustic Measurement Laboratory of the Institute of Applied and Computational Mathematics (IACM) conducts pilot experiments to record ambient noise in shallow and deep sea using self-made acoustic listener devices. Two experiments have been carried out so far for shallow sea in the bay of Heraklion, Crete. In April 2018, the first deep sea experiment was carried out in the Palaiochora area on the Southwest side of Crete at a sea site with depth of about 500 meters. Two autonomous loggers built in the IACM laboratory were used. The experiment had duration three days and, apart from the noise recordings, a calibration of the instruments was performed. In the present work, the experiment, the instruments used and their mode of operation are described, and the initial results are presented after analyzing the data collected.
Similarity measurements of acoustical and seismic signals using Hidden Markov Models
This work presents similarity measurements of acoustic and seismic signals using a machine learning approach based on a Hidden Markov Models representation of the wavelet coefficients of the signals. The measurements obtained by considering computational approaches for the estimation of the relative entropy between the corresponding models of the signals. The proposed scheme, initially performs a time-invariant feature extraction of the signal using the Stationary Wavelet Packet transform followed by a classification of these features by an appropriate Hidden Markov Model adapted after a training procedure, in order the signal to be characterized by a set of probabilistic parameters which are determined by the model. Using this scheme, the sequential patterns of the signals are taken into account in order to obtain a better and more noise tolerant signal characterization.
Acoustics and Education
Sound and acoustics training for undergraduate architects and teachers, two few-day workshops
Properties and behaviour of sound are required knowledge for both architects and educators. In this research we present two few-day workshops that were held in two different schools and concerned a non-special audience. The evaluation by the students highlighted the need to simplify the theory in order to communicate the basic concepts of sound and acoustics and to disseminate the tools and software related to the sound phenomenon, both in terms of understanding, synthesis, design and experimentation.
Schoolyard as a source of noise: Review of past work
This paper aims to examine schoolyard as a source of noise through a literature
review. Measured noise levels vary according to country of origin, level of education
and number of students involved. High noise levels are observed; this leads to the
conclusion that noise protection measures need to be considered for the school and
The Last Universal Common Ancestor: a project-oriented approach in teaching Digital Sound Processing
This paper presents an alternative approach in teaching the course “Digital Sound Processing” during the 6th semester of the academic year 2018-19 at the Department of Audio & Visual Arts of the Ionian University. This approach exploits the benefits of elements from the Experiential Learning Theory, as well as the of the field of Gamification for the realization of the 4-channel interactive audio installation “The Last Universal Common Ancestor”, with the aim of enhancing students’ motivation towards the learning process. The work evolves around symbolically mapping the evolutionary process of a living organism to an audio processing system of rising complexity and fidelity. The theoretical background, as well as all stages of the multi-faceted creative process are described in detail.
Sound Design for Film & Visual Arts
This work attempts to find aesthetic correlations between the visual arts and sound design for film, as well as to identify other intersections and parallelism with the sound technology. The direct objectives are: i) the use of these relationships as creative tools for sound design and for the synthesis of sounds in cinema and -in general- in narrative attempts through sonic media and (ii) application to educational processes for the teaching of sound design and, more generally, the synthesis of sounds in alternative cross-artistic and interdisciplinary ways.
The role of sound and space in action scenes and battles through three European films, Japanese, American and Chinese film
Cinematographic music and sound work in a similar way• they reinforce meaning, enhance mood and define viewer’s perception regarding the plot. But in an obvious way, cinematic sound and space that evolve in scenes of action and battle are not the same. The presented research analyses three characteristic action and battle scenes using a detailed analysis of music score and sound effects: Braveheart (1995) - America, Fightclub (1999) - America and Germany, Ran (1985) - Japan. Analysis of each scene is achieved by highlighting its visual and spatial dimensions. These parameters determine the identity, descriptive or interpretive, of each scene. The aim of this paper is to determine the elements that define its sound, acoustic and spatial character.
Noise and Vibration Control
Construction and study of the exhaust system of a race vehicle for noise reduction
This is a study of the construction and noise limit calculations of the exhaust system of a racing vehicle. The vehicle complies with the standards of the Formula SAE international student design competition it took part in.
The modelling of different types of resonators is done by the transfer matrix method both in Matlab and in specialized internal combustion engine software, WaveBuild.
Based on the modelling results resonators were constructed and tested by measuring the noise level in real life conditions. The measurement was the insertion loss, based on which the effectiveness of each resonator was deduced.
Phononic vibration absorber on a parallel level set-up
In this work, a structure that could act as a vibration absorber is being numerically studied. The structure due to its periodic characteristics could be considered as a Phononic Material and its study shows that, it can be a basis for its exploitation in this field. The calculated phononic band gaps along the transverse direction were very wide and cover a broad range of frequencies. The numerical method used was that of the finite differences in the time domain.
Applications of Vibrational Materials in Vibration Absorption
In this work, using the Finite Difference Time Domain method, we numerically examine the well-known Layer-By-Layer phononic crystal as a suitable candidate for applications in seismic protection of existing urban or countryside structures, monuments or any construction vulnerable to a seismic event. We investigate the response of the structure in different types of soil. All the geometry parameters of the structure were examined in our calculations.
Structure borne noise transfer function measurement, during the relocation study of a Laboratory of O.S.E.’s V.T.C., with the prototype vibrations oscillator BD-05.
The prediction of vibrations and structure borne noise in building application from vibration sources (e.x. E/M equipment) is a multiparametric investigation that is related both to the characteristics of the source (excitation frequencies) and those of the building itself (natural frequencies, noise-bridges, etc.). The characteristics of the source, such as excitation frequencies and dynamic load, may be available from the manufacturer or can be measures with the unit installed temporarily. On the other hand, the response of the building cannot be calculated, unless the whole building is analytically modelled. In this paper, a process is presented that allows for the measurement of the transfer function and the prediction of the level of vibrations and the structure borne noise with the use of a prototype vibrations oscillator.
The Patraikos Gulf Ambient and Seismic Noise Monitoring Project
This work presents the materials, methods and results of the West Patraikos Gulf ambient and seismic noise monitoring project, realized during the marine 3D seismic survey that was conducted by the Hellenic Petroleum S.A., in 2015. Dense acoustic noise monitoring data were acquired and processed close to the seismic source to as far as away from it, offering the opportunity to study the attenuation characteristics of impulse sounds in long distances. The extensive ambient noise monitoring that has taken place before and after the seismic survey, gave for first time evidence about the ratio of anthropophony to biophony in the area, by revealing fauna species and mechanical disturbances that control the soundscape.
Specialised antivibration system design for mechanical equipment’s vibration isolation in an office building
The study is concerned with the estimation and control of vibration caused by transformers located at the basement of an office building in Athens Greece. After thorough examination and on-site measurements of the vibration, we proceeded to design a specialized antivibration system the efficiency of which was estimated by a post-implementation set of measurements. The scope of this paper is to investigate methods of tracking and eliminating vibrations transmission that has a very significant effect not only on employees health and ability to work in an office building but also to the nearest residences acoustic comfort.
Speech and Voice Processing
Investigation of Double Compression Techniques for the Detection of Multiple Recordings in Audio Content
The goal of the current work is the tracking of different recordings within an audio file that was created from audio slicing or inserting segments of different files. We used audio files encoded in different formats (WAV, MP3, AAC) and different bitrates / compression ratios. Several audio segments are replaced with the same segments with different encoding in an automated and random way. In the proposed method under investigation the resulting files are recompressed. In the inserted segments where lossy compression has already taken place, redundant information has already been lost, so the information loss caused by the new compression process should be smaller. For every time window, an audio-feature vector is extracted from both files, the initial/tampered file and the double compressed file and the differences vector is calculated. The derivative of this vector is used to find where local maxima/minima are located, which possibly indicate the segments, where double compression has taken place.
Speech enhancement on the cloud by means of adaptive Wavelet-domain Wiener filtering
The current work focuses on the implementation of an online wavelet domain Wiener Filter denoiser (on the cloud), that is proposed for speech enhancement purposes. The outmost goal of the current project is to provide a quick and easy way to real-world speech denoising, with the easiest and most direct way feasible. Optimum configuration and adaptation aspects are thoroughly investigated, while multilevel performance analysis is conducted, using state of the art speech intelligibility metrics and criteria.
Somatosensory Training of the Lyric Voice by means of Acoustic Analysis in Interactive Environments
In this era of multimedia and internet, lyric singing education tends to incorporate new techniques and technologies connected to the acoustic and aesthetic perception of the voice. This paper introduces a novel method of modernizing singing training. We will present an application developed in LabMAT and its experimental evaluation. This software tool focuses on the feedback of the voice and somatosensory versus the more subjective auditory control of the vocal instrument.
Performative aspects concerning the prosodic utterance of the ancient Attic tragedies: Acoustical and phonological analysis
This study investigates the prosodic utterance of an excerpt from the part of Parodos, Aeschylus’ tragedy, The Persians (Persai), through the performance of six experienced university professors, musicians and actors. Their interpretations are based on scientific studies and experimental phonetic and psychoacoustic evidence, concerning the structure of the syllables, rhythm, accentuation, articulation and intonation. The main objective is to investigate the musicality of the ancient Greek language in Attic tragedies through the extraction of melodic and metric – rhythmic models using acoustical analysis of the main parameters of voice.
An Accessible Electronic Game based on Vocal Feedback
In this work we present the design, development and demonstration of a novel electronic game. The novelty of the implementation approach is based on the fact the graphics and sound (music and acoustics effects) engine are based on procedural creation techniques. That is, no pre-rendered graphics and pre-recorded sound is employed. Additionally, voice-driven interaction is also selected as the basic means for interacting with the game engine, thus allowing the characterization of the game as accessible, since it can be used by players with movement disabilities. Finally, the game is offered as an open source software, allowing for greater flexibility and adaptivity by the worldwide programming community. The game was demonstrated and tested thoroughly, and the obtained results showed that despite the lack of high-quality and resolution graphics and sound content, procedural creation and voice interaction still represent a means for delivering multiple genres of electronic games, including accessible ones.
Acoustics measurements, transmissions and materials.
Room Impulse Response, two-way source measurement system with active equalization and crossover functionality using variable sweep rate dual-channel method
The utilization of dual channel exponential sweep, implemented in frequency domain, with an arbitrary spectral content and constant temporal envelope. To divide signal into two channels, active crossover technique was applied. This implementation aims to utilize the characteristics of a typical sweep - i.e. high SNR, immunity to distortion or time variance - combined with the enhanced two-way speaker performance owing to equalization and sweep rate modulation adaptation to speaker’s response. This technique was applied in a software developed in the programming language Python. To test the proposed method in real measurements, a sub-woofer was designed and constructed, to be combined with an omnidirectional source as a combined two-way sound source.
Automating audio recording best practices on mobile devices
Evaluation of mobile applications serving sound measurement procedures demon-strate that the establishment of a “smart” framework for sound signal management of recordings for journalism/reporting needs is valid. In most scenarios concerning sound capturing for journalistic purposes, repetition of recording is not possible, and, thus, error detection during post-production can lead to the mandatory rejec-tion of recordings of unacceptable quality. The proposed framework includes tech-niques for the tracking of the sound level, reverberation time and semantic analysis of captured sound, providing the user with proper feedback, in order to avoid errors and ensure the improvement of overall recording quality. Such techniques concern signal spectrum and dynamics analysis, reverberation estimation and feature-based semantic analysis of the recordings.
Combining Digital Image Correlation and Acoustic Emission for Monitoring of the Strain Distribution until Yielding during Compression of Bovine Cancellous Bone
In this work, the surface heterogeneity in mechanical compressive strain of cancellous bone was investigated with digital image correlation (DIC). Moreover, the onset and progression of failure was studied by acoustic emission (AE). Cubic cancellous bone specimens, with side of 15 mm, were obtained from bovine femur and kept frozen at -20ºC until testing. Specimen strain was analyzed by measuring the change of distance between the platens (crosshead) and via an optical method, by following the strain evolution with a camera. Simultaneously, AE monitoring was performed. The experiments showed that compressive Young’s modulus determined by crosshead strain is underestimated at 23% in comparison to optically determined strain. However, surface strain fields defined by DIC displayed steep strain gradients, which can be attributed to cancellous bone porosity and inhomogeneity. The cumulative number of events for the total AE activity recorded from the sensors showed that the activity started at a mean load level of 36% of the maximum load and indicated the initiation of micro-cracking phenomena.
Graphene in electroacoustics
Vibrating membranes are the cornerstone of acoustic technology, forming the backbone of modern loudspeakers and microphones. The one carbon atom thickness graphene membrane has unique mechanical, electrical and thermal properties which make it attractive to acoustic technology since it can contribute in improving the efficiency and sensitivity of many acoustics transducer systems. In this work a summary for the application of graphene to audio technology is presented focusing on recent research papers as well as international patents. Applications are categorized as follows: (a) acoustic transducer electrodes; (b) vibration membranes for loudspeakers, microphones and earphones; (c) thermo-acoustic devices. Finally, the recent developments in the research and exploitation of graphene in acoustic technology are presented along with the future trends.
Acoustic behavior of flax reinforced polymeric matrix composite materials
Τhe present study aims at the acoustic study of polymeric matrix composite materials, reinforced with flax fibers, in particular the influence of the acoustic behavior of the composite on the orientation of the fibers. For the purposes of the experiments, laminated composite flax materials of 5 and 10-layer were fabricated via autoclave conditions and made of biaxial woven fabrics (0-90). Quality control of the laminated plates was performed by the C-scan method and the specimens were examined for their acoustic behavior in Kundt's acoustic impedance tube (made by Bruel & Kjaer). The results showed that there was no significant influence of the orientation of the fibers on the acoustic behavior of the material.
Sound reproduction from laser-driven sound sources (Laser Audio)
In this work, physical and technological aspects of the optoacoustic transduction through Laser Induced Breakdown are presented, with a focus on controlled reproduction of complex acoustic signals from optically-driven sound sources. The physical processes behind laser-induced breakdown from short, high-power laser. pulses are analysed and the experimental procedures and setups for precise measurements are described. Moreover, results from optical measurements are presented regarding different laser pulse energies and measuring distances, which allow for the characterisation of temporal and spectral features of the LIB acoustic signal. Finally, a LIB sound reproduction prototype is described and simulation results of reproduction of complex and continuous sound signals through LIB pulse trains in the air are presented and evaluated.
Surface acoustic waves in Au thin films deposited on glass substrates, generated by fs radiation
In this paper we present full-field measurement techniques, based on optical interferometry, for the analysis and characterization of high-frequency Surface Acoustic Waves (SAWs), generated by femtosecond laser pulses on a metallic film deposited on glass substrate. The dynamic response of the material is also numerically investigated and satisfactory agreement between experimental and numerical results regarding the propagation characteristics of SAWs is observed.
Ακουστική Συμπεριφορά Ανακαινισμένων Παλαιών Κιθαρών και Αντιγράφων τους. Συγκρίσεις
Musical instruments must be traced, where they are and are preserved as important elements of the world's material and intangible cultural heritage. The subject here concerns two guitars made in the 19th century, which are preserved in private collections in Kefalonia. Here, the procedures followed for the restoration of these old musical instruments will be presented and described in detail. Next, the production of copies, which produce similar, if not the same sound quality as the original instruments, will be presented.
Sound Synthesis Based on Social Behaviour in the Acoustic Domain
This work approaches the issue of sound synthesis by modelling the social behaviour of individuals / agents in the acoustic domain. The overall algorithm is the extension of the well-known artificial intelligence boids' model, which defines the context of the social interaction of the members of a cluster within a virtual space, with the basic objective of simulating the collective movement of living organisms, e.g. bird flocks and fish flocks. By extending this approach to the acoustic domain, the sonoids are defined, whose interaction is based on stimuli that are produced, transmitted and eventually received by these individuals exclusively through the acoustic channel.
Application of laser interferometric methods in the study of traditional and ancient Greek musical instruments
Full field laser interferometric techniques have been developed along with appropriate software for the process control and for data acquisition and analysis in real time that have been applied successfully for vibrational studies of string and percussion instruments.. Additionally, simulation methods based on Finite element models have been developed and validated from the experimental results. The studies of traditional and faithfully reconstructed ancient Greek instruments are of particular importance since they studied for the first time with these techniques.
Music Improvisation and Real-Time Interactive Computer Music based on Performer’s EEG Data Input
This paper presents an interactive application of musical improvisation entitled “Mental Palindrome”, which is based on real-time sonification of electroencephalography (EEG) signals. During the sonification process, the user performs improvised music while being inspired by the computer-generated music, thus creating a bi-directional process of feedback between the human performer and the machine. The sonification approach inputs the EEG data to modulate sounds and timbre, to select notes and melodies, rhythmic patterns and even uses gyroscope data to place sound in a typical 4-channel output audio system. Furthermore, the overall sound-synthesis process combines data related to facial expressions, thus targeting on acoustically representing any emerged user’s approximate emotional status.
Theoretical approach on the use of beams as musical idiophones
With the prospect of applying the results to musical idiophones such as the keys of vibraphone, xylophone or marimba, several cases of functionally graded beams are investigated mainly with regard to the eigenfrequencies they present. The bars can be modeled using either the Euler-Bernoulli or the Rayleigh model. In order to solve the eigenvalue problem an approximate method based on the Chebyshev polynomials is presented. To validate the method several cases found in the literature of uniform, nonuniform and functionally graded beam boundary value problems that have exact solutions, were used as benchmarks. We assume that the density of the beam varies either according to a trinomial and the Young modulus according to a 6th degree polynomial or to a trinomial. By varying the polynomial coefficients we are seeking integer ratios of the 3rd and 2nd bending mode eigenfrequency with respect to the primary vibrational mode. In most commercial instruments the tuning is done empirically by sculpting an arch on the underside of the bar. This way the frequencies are tuned in most cases to ratios 1:3:6, or 1:3:8, or 1:4:9.8. By varying the polynomial coefficients one at a time while keeping the rest of them constant we plot the frequency ratios. With this process we can detect cases where both frequency ratios reach integer values which pertain to a musically useful bar.
Augmented Reality Audio Games: a First Approach
This paper is a first attempt to converge the fields of Audio Games and Augmented Reality in the scope of creating Augmented Reality Audio Games, which will exploit the benefits of the two fields’ inherent characteristics and optimize the interactivity and immersion potential of the game experience. First, the most common sonification techniques, in particular those that realize sound spatialization, and the fundamental elements of audio game interaction are described. Then, the current directions, in which audio augmented systems have been applied, are presented. Finally, an advanced augmented reality audio mixer based on binaural loudness is suggested.
Relationship of the disturbance caused by environmental noise and the economy
The number of social surveys regarding citizens’ disturbance from environmental noise in Greece is relatively low compared to other European countries, where such surveys constitute a useful tool for strategic plans that aim in competing environmental noise.
Such a survey was carried out in 2007 by the School of Architectural Engineering, Aristotle University of Thessaloniki. The aim of the survey was to assess the impacts of environmental noise on the residents of the study areas. The results of that survey showed that noise levels in those areas were significantly high, reaching, in some cases, levels hazardous for human health.
It is widely known that in economic crisis conditions, environmental protection is regarded a ‘luxury’ by the State as well as by the citizens. Taking this attitude in consideration and the ongoing Greek economic crisis, a second survey was conducted ten years after the first one in the same area and with the same participants, to assess the extent to which economic conditions affect the way citizens perceive environmental noise.
The comparison between the two surveys is rather interesting.
Experimental Distributed Online System for Environmental Noise Measurements: Planning and Development
The purpose of this study, which emerged in the context of a diplomatic dissertation, was to develop a distributed system used to measure environmental noise remotely using a professional sound level meter. As an initial effort, a simple structure was used to implement the system with a single measurement station which the user can control from a webpage that is hosted in the servers of the electro-acoustics laboratory in Aristotle University of Thessaloniki. The system is composed of various smaller subsystems so that it becomes distributed and easily manageable. This way it becomes easier to further develop the system for future applications. Finally, after the evaluation of the resulting system, several related applications are described.
Acoustic comfort in open public spaces in the town of Edessa
The proposed announcement is part of a broader undergraduate research (2016-17), which was held at the Department of Architectural Engineering of the Democritus University of Thrace, concerning the bioclimatic facilities in Edessa's outdoor spaces and negotiates the study of the acoustic comfort conditions in public spaces (gardens / parks) of the city.
The research initially focuses on Edessa's urban development and the concept of acoustic comfort. It is presented the methodology of the survey, the twelve (12) selected areas of the city, as well as the criteria for their selection. Finally, the analytical and aggregate data are recorded and the conclusions of the survey are given.
All day bar in the city center of Thessaloniki: sound protection deficiencies 10 years later
In an older paper (2007) we examined the noise pollution in the center of Thessaloniki, due to all-day café bars (period 2005-06). The proposed paper continues the survey (period 2016-17) and proposes a comparative evaluation of the problem. New research data, using the same methodology, refer to a sample of 26 all day café bars, in the same area of the city center where in recent years there has been a great increase in the number of entertainment installations. The purpose of the recent paper is to identify the deficiencies in the licensing/ supervision of the all- day café bars and to correlated the dimensions of urban noise pollution to certain urban spatial planning parameters.
Evaluating a low-cost acoustic sensor for smart environments applications
Recent technological advances in both credit card sized PCs, in both performance and energy consumption, have opened new ways for a broader and more affordable research, by turning these computers into tracking devices through the development of wireless sensor networks. This paper describes and tests a low-cost acoustic sensor based on the Raspberry Pi 3 platform, which supports advanced sound field analysis functions. Besides presenting the system’s components, an evaluation of the audio recording capabilities of the nodes for the correct assessment of sound pressure level as well as of other acoustic parameters is carried out. Finally, the possibility of collaborative recording for sound source localization tasks, from a pair of nodes through the determination of the time difference of arrival of the sound, is studied and tested.
Ancient Greeks with their inventive mind had managed to design a bullhorn, a stentorphonic tube, with which they could transmit clear sound messages in big distances depended on the noise level of the environment of the receiver (dB) for a specific intensity level (dB) at the input of the stentorphonic tube.
The name stentorphonic tube was given because it sounded very loudly, just like the screams of Homer’s hero Stentor.
This bullhorn was used by Alexander the Great in order to lead the troops.
Homer’s sounds Recording, classification and comparison of sound phenomena appearing in Iliad and Odyssey
In Homeric poems many acoustic phenomena are described with such clarity that we are able to identify them with equivalents that can be described with scientific terms: Summation of sound pressure level of many sources, attenuation of sound pressure level, masking of sound and reverberation. The classification, apart from useful information of acoustic, literal, and archaeological interest, provides also the possibility of comparison: Iliad is characterized by the loudness of human voice and it’s masking by the battle noise, while the Odyssey is characterized by reverberation. This happens because Iliad takes place outdoors while Odyssey indoors. Τhe described sound phenomena follow this difference.
Archaeoacoustic Research on Caves dedicated to Pan and the Nymphs in Attica, Greece
Recent archaeoacoustic techniques, applied in ancient sacred grottos and other constructions, have paved the way for new research insights in ancient cult and ritual practice, offering the potential to enrich interpretations of how ancient buildings or natural spaces were perceived as loci of divine presence and worship. Here, the acoustic research was focused on selected examples of caves with known historic significance in ancient Greek societies. The caves were selected from a specific geographical region, Attica in Greece, where the combined worship of the hoofed-god Pan with his female companions, the Nymphs, was first organized and performed inside caves during the 5th century BC. The purpose of this inter-disciplinary research is to enhance our existing knowledge regarding the utilization of sound and acoustics during ritual ceremonies in caves, in an attempt to understand whether sound was a determining factor in the selection of caves as appropriate sacred sites. Although access to such caves introduces significant difficulties, acoustic measurements were obtained in two caves (Parnitha and Vari) at different source-receiver positions at locations where historic evidence indicates that such rituals were taken place. The single channel measurements were used for extraction of the acoustic parameters of the caves. For the same positions, binaural responses were recorded using a dummy head and these were later utilized via virtual listening scenarios for presentations and controlled evaluation of the cave acoustics by listeners in the laboratory using appropriate pre-recorded audio samples which according to the archaeological and historical data were reproduced during ancient rituals, made people believe that they were the abodes of these sacred spirits. The tests and analysis provide novel findings with regards to the suitability of cave acoustics for such ritual ceremonies.
Wave-based acoustic model of the Epidaurus theatre
In this work, new results are presented from wave-based simulations of the acoustics of the ancient theatre of Epidaurus, enabling the evaluation of paths with multiple reflections and diffractions. The study is based on two 3D models with different levels of geometrical detail. The parameters of the models were calibrated in accordance with existing measurements of the theatre’s impulse response in different auditory positions. The analysis highlights the contribution of diffracted sound in the theatre’s excellent acoustic performance, since diffracted paths appear to boost the mid-low frequencies, enhancing speech intelligibility, especially in the most remote auditory positions. It also becomes evident that the acoustic response of the middle auditory positions is the result of two distinct sound fields, one reaching the listener from the front (ascending field) and one from behind (descending field). Moreover, evaluations with different step geometries (leading to different tier inclinations) are carried out, showing the impact of the tier geometry to the theatre’s acoustic performance. Finally, it is shown that the placement of pillows in the front seating positions has a degenerative effect on the theatre’s acoustics.
Wireless Acoustic Sensor Network in the STORM Research Project for Archeological and Cultural Sites Monitoring
The STORM research project aims to provide critical decision-making tools to all European cultural heritage actors in charge of managing the effects of climate change and natural hazards. In this context and aiming to enhance the protection of monuments and archaeological sites, a wireless acoustic sensor network was designed and developed. The paper presents the sensor hardware and embedded software and provides preliminary results on the fidelity of the audio signals recorded by the network nodes.
Sound Classification in the STORM Research Project for Archeological and Cultural Sites Monitoring
The STORM European research project aims in developing an integrated set of technological and organizational resources for monitoring and safeguarding cultural heritage sites. In this context, wireless acoustic sensor networks that detect and record sound samples are deployed over cultural sites. The features of the recorded samples are calculated and forwarded to a feed-forward neural network for classification in order to extract information about the potential hazardous effect of the activity or activities that generated the sounds. Implementation details about the classifier and the sound features are discussed in this paper. Sound features are grouped with respect to their scalar or time-frequency nature and results are presented regarding the classification accuracy of each subset. Results are also presented regarding the accuracy of the proposed approach when operated in noisy environments.
Digital Sound Processing I
Statistical analysis of coloration in audio signals
Acoustic coloration is the audible distortion of a sound’s timbre, rhythmic sensation or pitch, which comprise the sound’s color . It is caused by sparse low-frequency resonances of small size rooms which correspond to their early, strong reflections. In this paper, we study the impact of coloration on audio features that describe the color of audio signals. Hence, we collected a set of anechoic (uncolored) signals, which was later colored by the early reflections of various rooms. Audio features were extracted from both these types of signals and the means of their values were compared with the use of paired samples t-tests. The results of. these tests led to feature evaluation and selection in terms of acoustic coloration. In the end, we conducted an analysis on the impact of coloration on values of features that were marked as statistically significant.
Stereo Image localization maps for loudspeaker reproduction in rooms
A novel approach is proposed for maps illustrating the accuracy of image source position reproduced by stereo systems in various scenarios of listening rooms / loudspeakers. Based on previous work by the authors, the maps unify results derived from an image localization classifier and the sweet spot area metric estimating the direction of arrival angles (DOA) of all potential image source positions reproduced by the system via a perceptual model. The statistical analysis of these maps indicates the skewness and kurtosis of the DOA classification error and hence the consistency and robustness of the image definition along the plane of listener positions. Results utilize such parameter mappings to objectively illustrate the robustness of this qualitative aspect of audio reproduction in rooms.
Investigating the relationship between auditory evoked potentials and tone-Burst stimulus intensity with neural networks
Early components of the auditory evoked potentials (AEP) reflect the neural processing of acoustic stimuli in the brainstem and the sub-cortical regions. Relating AEP patterns to their stimulus characteristics is a notoriously difficult task, due to the variability of their morphology. In this study, tone-Burst evoked auditory brainstem and middle-latency responses from 7 normal hearing subjects were used to develop a neural network model for the classification of AEPs depending on stimulus intensities. The raw AEP data was obtained from the study of Silva and Epstein (2010). Overall, results from this preliminary study indicate an accuracy of 85.2%, suggesting that the methodology developed should be further tested on larger data sets.
A Comprehensive Review of the Factors Affecting Inter-Subject Interaural Time Difference (ITD) Variability
This paper aims at presenting a comprehensive review of the factors affecting HRTF variability, by examining their combined and individual impact on the Interaural Time Difference. The analysis was based on data from the LISTEN, SADIE, and ClubFritz publicly available databases. According to the results, most of these factors caused perceptible ITD variations at least on a subset of the tested azimuth positions, fact which emphasizes the delicate nature of the acoustic HRTF acquisition procedure.
A method for up-mixing two channel stereo audio signals for surround sound reproduction
In this paper a low-complexity method for up-mixing two channel stereo signals for surround sound reproduction is presented. Based on a common stereo signal model, the panning coefficients and azimuth positions of the sources in the stereo mix are estimated. This information is then being used for the stereo signal decomposition and the re-synthesis to a multichannel signal for surround reproduction. The proposed method is evaluated through a subjective listening test.
Architecting an Audio Plugin Host as Web Extension
Building Acoustics I
Community performance spaces in Volos: Investigating and evaluating acoustic qualities and suggesting acoustical interventions
The area of research is the city of Volos. A city lacking in a main theatrical stage, hut with several community performance stages of smaller scale scattered in the urban fabric. The present paper attempts to summarize the methodology and criteria for assessing existing performance halls in the city. At the same time, it investigates and evaluates the case-study of the old Electric Company hall with the aim ofproposing a set of architectural and acoustical design solutions for the space, further resulting in a design and methodology> interventional strategy> that can be applied to similar halls and stages of the corresponding typology.
Acoustic correction in large coupled volumes: the roofed atrium at the new Town Hall of Thessaloniki
In this paper we attempt to prove that the effective acoustic design of a space with coupled rooms (through the prediction and dispersion of sound-absorbing zones, without diversifying the architect design) can achieve greater goals than the effective control of the reverberation in a large and variform area of gathering and public serving. The purpose of the acoustic correction of the atrium in the new Thessaloniki City Hall was the effective reduction of the reverberation time (from 4 - 4.7 sec at the average frequencies, to the tolerable limits of 1 - 1.6 sec) due to the functioning of an open and exposed space which is composed with various sizes coupled spaces with openings of different dimensions. Furthermore, occasionally the atrium also serves events of speech (with electro-acoustic support), or live music events, with gathering of artists and audience on the ground floor.
Contemporary architecture and outdoor acoustic shells
Outdoor acoustic shells are architectural constructions placed in open public spaces to host music concerts. This work aims to highlight the importance of a holistic approach of acoustic design in auditorium's open air architecture, using characteristic examples of the evolution of acoustic shells’ design during the 20th century. The examples are examined on the basis of their architectural and acoustic quality and their construction characteristics.
The Lombard effect in spaces for social gatherings; literature review and methods for its control
The Lombard effect describes the phenomenon of background noise increase due to simultaneous verbal communication. The aim of this study is to discuss the Lombard effect in spaces for social gatherings. A literature review is presented as well various guidelines regarding its control.
Αρχιτεκτονική και Ακουστικός σχεδιασμός Στούντιο Ηχογράφησης
Η παρούσα εργασία αποτελεί μέρος της πτυχιακής ερασίας του πρώτου εκ των συγγραφέων στη Σχολή Αρχιτεκτόνων ΕΜΠ. Σε αυτήν αναλύονται η σχέση της ακουστικής και της αρχιτεκτονικής studio ηχογράφησης μέσα από υλοποιημένα παραδείγματα αναγνωρισμένου κύρους. Επίσης προτείνεται συνθετική προσπάθεια σε σκαριφήματα ως εφαρμογή της ανάλυσης που προηγήθηκε.
Drama theatres of modernity in postwar Hellas; Physical acoustic measurements
This paper aims to examine the acoustical performance of drama theatres of modernity in postwar Hellas, in relation to their architecture. Acoustic measurements were carried out in seven theatres. Two theatre types are observed in this period, namely the type “less is more” and “detached” theatres. The first theatre type is usually hosted in the basement of multistory modern buildings. the other theatre type occupies an entire building in itself. It is demonstrated that the human scale which is adopted by the theatre type “less is more” works synergistically with good acoustics. by contrast the other theatre type needs additional building elements to achieve satisfactory sound performance. The present results illustrate the implications of architectural design on the acoustical performance of the theatres and demonstrate, by and large, the acoustical merits of the test auditoria.
Digital Sound Processing II
Network Music Performance: A client side interface to control audio streams using Gstreamer and GTK open frameworks.
We have implemented a client application to perform online music sessions with which the musician - user controls the start and transmission of audio to and from the server as well as point-to-point transmission and reception. We made measurements focusing on the mouth to ear delay and how this is affected by parameters such as the size of the Ethernet packet, the cache size, and we present the results for various audio compressions and uncompressed audio.
Web radio automation and "big data" of audio (and audiovisual) semantic annotation
One of the main issues of radio broadcasters is content documentation and management. For this purpose, various techniques have been developed, utilizing machine learning algorithms for the segmentation, recognition and classification of sound events. Advanced deep learning methods and hybrid /combined approaches are currently deployed, pursuing more sophisticated semantic conceptualization and analysis outcomes. However, the limited availability of properly annotated datasets is undoubtedly one of the most critical problems in the training and evaluation of such smart systems. This paper proposes a novel web-radio automation system that, besides audio playlist and mixing management, it records events and actions of the streaming process, thus automatically producing suitable sound datasets with high quality and accuracy annotations.
Study and application of the pole-fitting method in headphones equalization
The reproduction of audio signals with headphones often degrades due to spectral response deteriorations, colorization and attenuation or cancellation of different frequencies or frequency ranges, depending on the technical characteristics of each model. To address this problem, the practical application of the well-defined equalization method with pole fitting in the spectral responses of three different headphones using tree equalizer target functions, is studied in this work. The subjective and objective evaluation of the results demonstrates the satisfactory correction of the responses of the headphones with relatively low computational costs.
Open optical-electronic platform for creating and reproducing sounds through gestures.
With the passage to the digital age and the tremendous evolution in microprocessors, many artists turned to electronic music. In our work, an open platform (set-up) of music creation through optical-electronic interfaces (sensors) is presented. It exploits man's kinesiology by combining laser beams and interfaces whereby, through a microcontroller, it creates or reproduces a multitude of musical joints as a real MIDI general controller. Sensors of metallic conductive materials, conductive pigments, as well as ultra-thin, transparent and flexible graphene films or graphene-related materials were studied. The results are quite satisfactory with high responses. The ease of creation and reproduction through this platform could make it a learning and entertainment tool, and maybe a music therapy tool.
Real-Time detection, classification and DOA estimation of Unmanned Aerial Vehicle
The present work deals with a new passive system for real-time detection, classification and direction of arrival estimator of Unmanned Aerial Vehicles (UAVs). The proposed system composed of a very low cost hardware components, comprises two different arrays of three or six-microphones, non-linear amplification and filtering of the analog acoustic signal, avoiding also the saturation effect in case where the UAV is located nearby to the microphones.
Advance array processing methods are used to detect and locate the wide-band sources in the near and far-field including array calibration and energy based beamforming techniques. Moreover, oversampling techniques are adopted to increase the acquired signals accuracy and to also decrease the quantization noise. The classifier is based on the nearest neighbor rule of a normalized Power Spectral Density, the acoustic signature of the UAV spectrum in short periods of time. The low-cost, low-power and high efficiency embedded processor STM32F405RG is used for system implementation. Preliminary experimental results have shown the effectiveness of the proposed approach.
Building Acoustics II
The acoustics of Aris Garoufalis Hall at the Athens Conservatoire
The current paper examines the technical approach as well as the results of the acoustic study conducted for the "Aris Garoufalis" hall of the historical Conservatory of Athens. Due to architectural design limitations, minimal but necessary construction interventions were proposed. Numerous acoustical measurements were performed in order to capture the project’s progress level and to highlight key issues that eventually emerged as a result of design deviations from the original plan. Particular emphasis was placed on the importance of the choice of the seats in the room as well as on the impact of the incorrect application of acoustic surfaces, demonstrating their considerable influence on the main indicators of acoustic quality. Finally, the paper demonstrates the "inevitable" comparison of the acoustic prediction model with actual measurement results as the room modelling process became an essential part of the design approach.
Conversion of a building envelope of the industrial complex “Allatini” in Thessaloniki to a variable acoustics auditorium.
This paper presents the design of conversion of the reserved envelope of “Βuilding 24” of the industrial complex “Allatini” in Thessaloniki into a variable acoustics auditorium, capable of accommodating both music and speech events. Its shoebox design demonstrates variable accommodation capacity by its conversion into two smaller auditoriums, with appropriate variable acoustic behavior. The acoustic design is performed based on the combination of geometrical design of reflectors with the method of images and the statistical – energy calculation method of reverberation time. The variable acoustics behavior is achieved by the use of variable sound absorption on the inner side of the building envelope. The design is being validated with an acoustic behavior simulation with the use of CATT Acoustic.
Library Acoustics Improvement: Case Study for the Technical University of Crete
The use of academic libraries has expanded in recent years to adapt to changes in technology and society. Hence, different acoustic requirements are necessary which are often not taken into account in the design process. This study is carried out with the aim of improving the acoustics of the existing library of the Technical University of Crete.
In the library area, impulse response measurements were performed at three different levels and at a sum of six measurement points. Reverberation time was then calculated. Sound levels were recorded in the time domain as well with the main sources of noise (steps, speech etc.).
From the results of the measurements two are considered the most important problems whose solution is a priority for the improvement of the library acoustics: the fluctuating sound levels and the high reverberation time. To address these problems, several solutions are proposed, the most important of which are: segregation of spaces into zones with the fitting of suitable frames and the placement of absorbent materials.
In conclusion, the solutions proposed for the improvement of acoustics of the library of the Technical University of Crete and existing libraries include a framework of acoustic and non-interventions to achieve the best possible result.
Ο ρόλος του συμβούλου ακουστικής - Προβληματισμοί και εμπειρίες από την ακουστική μελέτη και την κατασκευή του Κέντρου Πολιτιστικού του Ιδρύματος Σταύρος Νιάρχος
The Stavros Niarchos Foundation Cultural Center has already opened since 2017 and acts a multidisciplinary landmark that accommodates the Greek National opera and the Greek National Library. This majestic complex resides in an ecological natural landscape hosting at the same time an extensive closed parking area.
Along with the main performance hall the SNFCC holds a second smaller multipurpose hall (experimental stage), rehearsal rooms for the choir, the orchestra as well as ballet rooms and numerous individual warm up rooms for the musicians.
During its design and construction the top notch specs infused in all the building’s parts, required the continuous, meticulous and responsible contribution of every single person involved in the project. Adding to the above the challenging time scheduling, the implementation of the acoustic design guidelines consisted of very demanding tasks the throughout the entire duration of the project.
The present paper is discussing the role of the Acoustic Consultant in projects of such scale and function using examples from the personal experience of the authors who acted as the executive acoustic consultants of the project from conception to completion.
Study of the acoustic behavior of rooms in terms of statistical analysis of acoustic measurements
The specific work deals with the estimation of the mixing time based on room impulse response measurements, using statistical analysis methods. The studied methods are based on the temporal evolution of the statistical measures of normalized kurtosis, Fisher information, Shannon entropy and Tsallis entropy. Their estimation accuracy is evaluated and the conditions for their reliable application are discussed on the basis of the analysis of different room impulse responses and the comparison of their results with those produced by mathematical models suggested by the literature.