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Session 13 - Miscellanea

Visualization of sound fields with application to musical instruments
N E Molin
Luleå University of Technology, Experimental mechanics, Luleå, Sverige

Modern optical measuring methods have the advantage of being contact less, non-disturbing and whole field methods. They often are quantitative and they present "pictures". In the following some modern optical, holographic, speckle and interferometric methods that visualize and measure vibrations and sound fields of musical instruments are presented and discussed.

Conversion of Jordao's theatre hall into a concert hall - study of its acoustical properties
L Braganca¹, J Patricio², B Belo¹
¹Universidade do Minho, Engenharia Civil, Guimaraes, Portugal; ²Laboratorio Nacional de Engenharia Civil, Acoustics, Lisboa, Portugal

The aim of the work presented on this paper is to characterize Jordao's Theatre Hall acoustical performance, in order to study the ability for its conversion into a Concert Hall. Jordao's Theatre Hall at Guimaraes, Portugal, was built in 1938. With a rectangular form, an audience volume of 5632,00 m3, it has a capacity of 1220 seats, distributed by two order levels. This characterization is done as follows: - Acoustical measurements of Reverberation Time and Clarity in situ; - Computation of the Hall using E.A.S.E. 3.0 software; - Comparison between both previous responses in order to achieve the best accuracy between computer simulation data and the results obtained in situ. The test results confirmed the conclusions of current empiric observations. Due to orthogonal Hall configuration, in terms of walls and its combination with a flat ceiling, as well as due to low sound absorption of almost every exposed surfaces, the listening quality of the Hall is very poor. Therefore, a study of acoustical correction was made, based on computer simulation of different proposals, in order to improve its ability to carry out several types of musical performances. The derived guidelines are thus presented in the conclusions of this paper.

Music acoustics in the curriculum of the Spanish music degrees
J Bretos
Departamento de Física, Universidad Pública de Navarra, Spain

There has been recently a deep change in the music curriculum in Spain. Previously, music degrees consisted mainly of an accurate technical training to perform an instrument virtuously. Even, conducting and composing were a bit overshadowed in comparison with performing. So, theoretical matters, like History and Aesthetics of Music, Harmony or Music Acoustics, were included in a set of secondary subjects that students could follow in a very free way. On the contrary, present music education combines suitably all the different aspects of the musical training and balances well theoretical and practical aspects. These changes have benefited Music Acoustics in particular. So, all music students must attend at least sixty hours of this subject. Most of them have had a very good reaction with the subject due to three main reasons. First, Music Acoustics allows them to understand the physical basis of music. It is a valuable achievement because most of the students have a humanistic education rather than a scientific one. Second, Music Acoustics helps them to understand better many concepts of theory of music like pitch, timbre, intervals or chords. Third, the subject also includes the study of the historical and technical development of musical instruments, which was often neglected in ordinary lessons of History of Music.

Why should a musician study acoustics?
M Campbell
School of Physics, University of Edinburgh, UK

University music students are sometimes dismayed to discover that among the subjects they are expected to master is the "scientific" topic of musical acoustics. The first aim of the teacher of musical acoustics must be to break down this barrier, and to convince the musicians that they can indeed learn something valuable from studying the physics and psychoacoustics of music. This talk explores some ways in which this goal can be approached through demonstrations involving musical instruments.

Leak detection in musical wind instruments using acoustic pulse reflectometry
V Chilekwa, D B Sharp
Open University, Environment and Mechanical Engineering, Milton Keynes, United Kingdom

In this paper, the technique of acoustic pulse reflectometry is applied to the problem of leak detection in tubular systems, such as musical wind instruments. Acoustic pulse reflectometry is a method for measuring the input impulse response of a duct. Suitable analysis of the input impulse response enables changes in area along the duct to be calculated. The presence of a leak results in a spurious increase in the calculated cross-sectional area at the position of the leak. Results are presented which shows that there is a correlation between the rate of change of cross-sectional area and the size of the leak. Finally, the applicability of the technique to musical instruments is illustrated with measurements made on historical wind instruments.

An EDS modelling tool for tracking and modifying the musical signals
B David, G Richard, R Badeau
Telecom Paris (ENST), Signal and Image Processing, Paris, France

When one intends to achieve a good sound quality in applying classical effects like time stretching or pitch shifting to a piano recording, the problem of separating the stable sinusoidal components from the mechanical noise has to be addressed. This decomposition allows for specific processing of each part. In the case of the piano, the effect must indeed be applied only on the sinusoidal part to preserve the naturalness of the sound, especially if the amount of the stretching or the shifting is large. In this paper, an adaptive parametric method is presented, based on an Exponentially Damped Sinusoidal (EDS) model for the signal. This technique is not limited by the well-known trade-off between the spectral resolution and the length of the analysis window as in classical Fourier based approaches (for instance the phase-vocoder). The signal subspace is directly tracked and the poles related to sinusoidal components are selected regarding the stability of their time trajectory. Some recent enhancements of the algorithms for audio signal processing are demonstrated; in order to achieve a lower complexity. The musical applications include modifications of piano sounds and the singing voice.

Didactic resources for the teaching and popularisation of the physics of the music
M J Elejalde-García, E Macho- Stadler, A Franco-García, J Janariz-Larumbe
Universidad del País Vasco, Escuela Superior de Ingenieros, Bilbao, Spain

The physical knowledge about the nature of the sound is shown desirable and necessary for students, players and the enthusiastic to the music in general.
This extensive population implies the creation of didactic materials with easy access and coherent, simple and multiple forms of presentation of the following themes:
- the physical and musical characteristics of the sound
- the qualities of the musical groups and of the auditoria
- the fundamentals and acoustical possibilities of the instruments
- the peculiarities of the voice and the human ear
- the relation among the music and the new technologies
- the musical peculiarities of the folk tradition.
The didactic units include book, web page or CD formats and have served of support for university free-election subjects about musical physics. Students have mainly proceeded of the engineering field and other didactic resources as the laboratory, the videos and the tutorials have been utilized. The student's opinion about the methodology and materials has been in favour of the simplicity and scientific rigor without an extensive use of the mathematical language. This has encouraged us towards the same informational effort, directed to people that are not familiars with mathematics and physics.

Quantitative assessment of air flow from professional bass reflex systems ports by Particle Image Velocimetry and Laser Doppler Anemometry
E Esposito, M Marassi
University of Ancona, Department of Mechanics, Ancona, Italy

Particle Image Velocimetry is a well known laser based measurement technique that un-intrusively determines the instantaneous full field velocities of a fluid flow. It uses two laser pulses to produce two images of a flow seeded by small particles; specialized software packages cross-correlate these images and process them to extract vector maps. Also Laser Doppler Anemometry employs laser light to remotely determine fluid flow velocities, but to do so, it exploits laser beam Doppler scattering from seeding particles. In this work we will present a series of experiments conducted on different bass reflex ports designs to assess their performance in terms of flow turbulence and sound level compression at high input power levels. These issues are quite important in professional sound systems, where increasing power levels and sound clarity ask for exponentially growing cost and weight. For these reasons it is vital to optimize port design and our tests have been conducted on a well known 400 W system normally used in medium sized venues and on a custom built similar box.

Computer-animated illustrations of vibrations and waves
D E Hall
California State University, Physics, Sacramento, United States

Students in Musical Acoustics courses often do not have much experience either with concepts in physics or with graphs as a representation of physical systems. We do well to provide as much as possible in the way of demonstrations to illustrate these concepts, and computer animations can be a valuable supplement to physical demonstrations. The author has written a set of eleven programs in QBasic 4.5 for the PC, which are complementary to a similar set done by Bruce Richards in C++ for Macintosh users. The programs include depictions of basic physics (Doppler effect and normal modes), motion of plucked and bowed strings, motion of struck bars and drumheads, and air motion in various classes of pipes. Many of these are "movie versions" of illustrations in the author's textbook, and several will be demonstrated.

Musical acoustics courses in the education of music students in the U.S.A.
D E Hall
California State University, Physics, Sacramento, United States

Musical Acoustics courses in American universities and colleges, and the textbooks written for them, have developed largely for the sake of General Education courses whose purpose is to provide token exposure to science for students majoring in other subjects. The author is not aware of any substantial previous data showing whether these courses play a significant role in the training of music majors. A survey questionnaire has been sent to the heads of all music programs accredited with the National Association of Schools of Music. The results provide new information about the number of schools that have Musical Acoustics courses available, and the proportion in which this course has some integral role as a required or recommended part of the student's program.

Unusual motions of a nonlinear asymmetrical vibrating string
R J Hanson¹, H K Macomber¹, A C Morrison²
¹Univ. of Northern Iowa, Physics, Cedar Falls, IA, United States; ²Northern Illinois Univ., Physics, DeKalb, IL, United States

A rich variety of unusual motions of a sinusoidally driven vibrating string results from nonlinearities due to varying tension and longitudinal motion not included in simple linear theory and to intrinsic asymmetries in the string. In a brass harpsichord string(wire) the asymmetries cause a small splitting of each natural frequency of free vibration into two closely spaced frequencies (relative separation ~ 0.2% to 2%.) The two frequency components are associated with transverse motion along two orthogonal "characteristic" wire axes. The absolute amount of splitting for a given wire is inversely dependent on the tension. Introduction of a twist in the wire can also affect the amount of splitting. These asymmetric properties have a profound effect on the nonlinear behavior. Detailed measurements of the resulting features of the motion of a driven string have been reported (Hanson et al., Proceedings of ISMA 2001, pp. 157-160.) Generation of higher harmonics and of motion perpendicular to the driving direction result in elaborate motions which can suddenly change from one state to another. Emphasis will be on some motion patterns of a point on the wire as exhibited on videotape (e.g., one appearing almost chaotic but with a pattern period of over 10 seconds.)

Reducing the source tube to improve the bandwidth of acoustic pulse reflectometry
A Li, D Sharp
The Open University, Environmental and Mechanical Engineering, Milton Keynes, United Kingdom

Acoustic pulse reflectometry has become established as a useful non-invasive technique for measuring the input impulse response, input impedance and internal dimensions of tubular objects such as musical wind instruments. The technique involves sending a sound pulse via a source tube into the object under test then recording and analysing the resultant reflections. The source tube is necessary to separate the forward and backward travelling pressure signals. However, attenuation of these signals while travelling in the source tube can be significant. In this paper, an alternative method of calibration is presented which enables the source tube to be shortened. Attenuation of the input and reflected signals is reduced resulting in input impulse response measurements of improved bandwidth and more accurate bore reconstructions.

From block-diagrams to C code
Y Orlarey, D Fober, S Letz
Grame, Centre National de Creation Musicale, Lyon, France

Block-diagrams are used to represent a broad variety of systems ranging from biological models to electronic circuits. From the cognitive point of view, block-diagrams provide an efficient way of describing a system in terms of subsystems and their relations. Many visual programming languages take advantage of this fact and use blockdiagrams to represent programs. While several computation models can be attached to a block-diagram, the data-flow model is probably the most popular one. Because of its apparent simplicity the data-flow model is very appealing. In the computer music field for example, most of the visual languages proposed are directly inspired by this model. But actually the semantic of the data-flow model can be quite complex and depends on technical choices like, synchronous or asynchronous computations, deterministic or non-deterministic behavior, bounded or unbounded communication, FIFOs, firing rules, etc. For these reasons defining the formal semantic of block-diagram languages based on data-flow models is not trivial, and the majority of the data-flow inspired music languages have no explicit formal semantic. In this paper we introduce a new algebraic representation of block-diagrams and we propose to adopt a functional model of semantic instead of a data flow model. Based on these elements we show how to implement compilers able to translate DSP blockdiagram specification into efficient C code that can compete with a hand written code.

An apparatus for measuring string vibration using electric field sensing
J Pakarinen, M Karjalainen
Helsinki University of Technology, Laboratory of Acoustics and Audio Signal Processing, Espoo, Finland

Vibrating string measurements by electric field sensing make use of the phenomenon where the capacitance between a metal string and an electrode plate changes as a function of the distance between them. The measuring device introduced in this study is intended for measuring the vibrational movement of a conductive string in two polarizations and possibly in multiple points. The basic idea of the construction is to apply an alternating voltage of high enough frequency to the string, and to measure the capacitively induced voltage from a small electrode plate nearby. This AC voltage is amplitude demodulated to obtain the displacement of the string as a function of time. The simple architecture of the measuring apparatus, its relatively small size, and minor effect to string vibration make it an interesting alternative to other string vibration measurement devices. Detailed construction of the apparatus will be described in the paper, as well as analysis on its properties. These include the accuracy of the method, the dynamic range of vibration that can be achieved, and system design parameters that affect these properties. Interesting cases of string vibration (particularly of the guitar) will be analyzed and depicted. Finally ideas for future developments are presented.

Automatic segmentation and transcription of radio broadcasts containing music and speech
K Sjölander
KTH, TMH, Stockholm, Sverige

A novel method for automated segmentation and transcription of audio has been developed which borrows ideas from the fields of Machine Learning and Automatic Speech Recognition. The method utilizes an ensemble of Hidden Markov Models (HMMs) to decode the contents of an audio signal. The result is a description where the signal has been divided into segments and where each of these segments have been assigned a label from a predefined set. Categories could for example be silence, music, or speech. But more detailed classes can also be used. For example, speech can be segmented at a finer phonetic level. The method has been implemented in a software system for audio processing and has been tested on recordings from the Swedish broadcasting corporation. The system is able to provide automatically aligned segments, that are more than 90% in agreement with those provided by manual segmenters, given a 20ms tolerance. These results are competitive with other published results. Segmentations created by automatic methods have the attractive properties of being cheap, consistent and reproducible.

Measurement of the termination impedance of a tube using particle image velocimetry
D J Skulina, D M Campbell, C A Greated
University of Edinburgh, Acoustics and Fluid Dynamics Group, Edinburgh, United Kingdom

The non-linear behaviour of the acoustic velocity field in the vicinity of the open end of a musical wind instrument is strongly affected by its detailed geometry. As the sound pressure level within the instrument increases phenomena such as acoustic streaming and vortex shedding contribute increasingly to the dissipation of sound energy, resulting in an increase in the real part of the terminating impedance. To characterise quantitatively the effect of varying the geometry of a tube termination, particle image velocimetry (PIV) has been used to measure the velocity field near the open end of a tube in which a high amplitude sound field is generated by a loudspeaker. A high speed digital camera and pulsed laser were used to acquire imageswith high spatial and temporal resolution from which velocity maps were derived. Three tube ends with different profiles were studied. The acoustic volume flow was obtained from the PIV maps and the sound pressure level measured using a probe microphone, allowing the terminating impedance to be calculated at a number of sound levels. In addition, the full field velocity maps obtained using PIV allow a qualitative description of the development of the acoustic flow at the tube termination as the intensity increases.

Direct measurement of the 3-D acoustic impedance in wind instruments near field.
D Stanzial, D Bonsi
FSSG-CNR, The Musical and Architectural Acoustics Laboratory, Venezia, Italy

An application of the Microflown® probe for directly measuring the acoustic impedance in the near field of wind instruments is here presented. After a careful calibration process carried out at our Lab using the stationary tube method, the 4 electrical outputs from the probe were demonstrated to be effective analog signals of the acoustic pressure and the three spatial components of the particle velocity at the measurement point. The probe has then been used for measuring the 3-D impedance in the near field of an open organ pipe and other wind instruments played within a dead room. A short review of the obtained experimental data, with special emphasis to different fingerings in woodwinds playing, is discussed and the potentiality of this method for musical acoustics is addressed.

Measurement of standing wave patterns in ducts using particle image velocimetry
A Tonddast-Navaei, D B Sharp
Open University, DEME - Faculty of Technology, Milton Keynes, United Kingdom

Particle image velocimetry (PIV) has successfully been used over the past two decades in the field of fluid mechanics for the non-invasive measurement of flow velocities. Advances in technology have recently enabled the technique to be used to determine particle velocities in acoustic fields.
In this paper, measurements of standing wave patterns in a simple square cross-section duct are presented. The duct was driven at its first few resonance frequencies and the variation in acoustic particle velocity amplitude along the duct at each frequency was measured using PIV. Similar measurements carried out using ducts with more complex geometries are also presented.

Sound and vibration from a special musical instrument: the Mazzacorati theatre
L Tronchin¹, E Esposito², V Tarabusi¹
¹University of Bologna, DIENCA - CIARM, Bologna, Italy; ²University of Ancona, Mechanical Dept., Ancona, Italy

The sound characterisation of theatres represents a common target especially for architects and acousticians. Italian theatres are usually characterised by their special horse-shoe shape, and only acoustical measurement are performed. The "Teatro of Villa Mazzacorati", in the town of Bologna, Italy, represents a little, unique baroque wooden theatre, where young W.A. Mozart played during his stay in Bologna, which is quite similar to a huge violin sound-chest. Never measurements were performed in the hall and in the only balcony. Therefore, vibro-acoustical measurements were planned. Experimental acoustical values have been obtained by using of a dummy head (Sennheiser) and a 3D microphone (SoundField), while vibrations have been measured by using a Laser Doppler Vibrometer (LDV). Both the technique allowed the measurements of IRs in listening positions. The results were compared and presented.

Large-bandwidth measurement of acoustic impedance using two microphones and four calibrations
M O van Walstijn, D M Campbell
University of Edinburgh, School of Physics, Edinburgh, United Kingdom

Musically useful information about the internal bore of musical wind instruments can be obtained by measuring its response to an acoustic input signal. Both frequency- and time-domain methods have been developed for this purpose in the past few decades, each having their specific advantages. A major difficulty with most of these methods is to obtain accurate response information at the higher frequencies. Frequency-domain methods for measuring the input impedance are usually based on certain low-frequency assumptions, while with time-domain methods it is usually difficult to inject sufficient high-frequency energy into the excitation signal. One of the key-features of a suitable method is that it should be insensitive to the influences of local non-propagating modes, which are typically significant for short wavelengths. In this paper we propose a method that measures the planar mode input impedance at frequencies below the first cut-on of the measurement duct. It is shown that accurate measurements are possible up to 20 kHz, using a new calibration method that does not depend on accurate knowledge of the propagation constant. Furthermore, we discuss the application of the measurement data to reconstruction of the internal bore profile.

Breathing modes of woodwind bodies: Experimental detection with ring-shaped piezoelectric-polymer sensors
M Wegener¹, R Gerhard-Multhaupt¹, W Wirges¹, A Bergner², S Bergweiler²
¹University of Potsdam, Department of Physics, ACMP, Potsdam, Germany; ²University of Potsdam / UP Transfer GmbH, Department of Physics, ACMP, Potsdam, Germany

For the operation of wind instruments, the breathing of their bodies plays only a secondary role. But especially in woodwinds, the change of the cross-sectional area may influence the sound (1) by radiation "secondary" sound waves and (2) by changing the boundary conditions for the sound field inside the cylindrical resonator, which will in turn affect the sound radiated from the instrument.
Here we present a special measuring technique for detecting wall movements of cylindrical resonators. A piezoelectric sensor film is slightly tensioned around e.g. an organ pipe and used to measure the cross-sectional oscillation of its body. A possible disadvantage of this technique as compared with interferometry or acoustical measurements may be a slight restriction of the body-wall breathing by the tensioned piezoelectric film, but the advantage is a complete recording of the breathing for the full circumference of the cylindrical body. We discuss the body-wall breathing observed on different types of organ pipes. With patterned electrodes on the piezoelectric film, it was also possible to directly detect the ellipsoidal dipole-like oscillation of the upper lip and the upper end of organ pipes, which is already known from interferometric measurements.
In general, the proposed sensor can be employed to characterize body-wall breathing oscillations of woodwinds independent of tube material and surface smoothness.

Teaching Musical Acoustics to musicians, why?
M Zenker
Escuela Nacional de Música, Universidad Nacional Autónoma de México, México

Through teaching Musical Acoustics and the comprehension of basic and specific acoustical phenomena, music students should be able to learn faster certain aspects in musical training, develop scientific criteria and have elements to understand useful scientific articles related with their profession in order to improve in their professional life. Prejudices should be wept out, the first of them that musicians, by learning acoustics, will loose the needed "emotion" or "feeling" to play o make music properly. Musical Acoustics should also help to comprehend some of the difficulties of adjusting musical instruments and the boundaries between what is a problem of the player, what a problem of the instrument and what an acoustical problem for itself.

Refractoscopic visualisation of sound in musical instruments
L Zipser, H Franke
ZAFT Centre of Applied Research and Technology at HTW Dresden, Electronics, Dresden, Germany

The problem of sound generation and emission in musical instruments has been investigated by several researchers for a long time with different results.
Now, a new method for measurement and visualisation the generation and irradiation of sound was developed and tested by the authors. This non-contact method is based on an usual laser-scanning vibrometer. It can be used for measuring and visualising acoustic sound and turbulence fields in air. As measuring effect is used the variation of the optical refractive index in air, caused by acoustic sound or turbulence. This justifies the name "refractoscopy". Refractoscopy is qualified for investigating and presenting numerous acoustic and fluidic phenomena and their interaction. For the first time the generation and the propagation of air born sound can be investigated simultaneously with the same method.
The paper is concerned with the refractoscopic investigation of the generation and irradiation of sound from wind instruments, e.g. organ pipes, flutes and trumpets. The phenomena of the changing of the acoustic impedance on the output of wind instruments was made visible at different frequencies. In addition the sound irradiation of vibrating instrument bodies, e.g. violins are shown.
The animated presentation of the measuring results as videos is impressive and instructive. In the field of education and instrument design refractoscopy has a large potential to make acoustics clearer and readier for application.

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