The KW-boundary hybrid digital waveguide mesh for room acoustics applications

The digital waveguide mesh is a discrete-time simulation used to model acoustic wave propagation through a bounded medium. It can be applied to the simulation of the acoustics of rooms through the generation of impulse responses suitable for auralization purposes. However, large-scale three-dimensional mesh structures are required for high quality results. These structures must therefore be efficient and also capable of flexible boundary implementation in terms of both geometrical layout and the possibility for improved mesh termination algorithms. The general one-dimensional N-port boundary termination is investigated, where N depends on the geometry of the modeled domain and the mesh topology used. The equivalence between physical variable Kirchoff-model, and scattering-based wave-model boundary formulations is proved. This leads to the KW-hybrid one-dimensional N-port boundary-node termination, which is shown to be equivalent to the Kirchoff- and wave-model cases. The KW-hybrid boundary-node is implemented as part of a new hybrid two-dimensional triangular digital waveguide mesh. This is shown to offer the possibility for large-scale, computationally efficient mesh structures for more complex shapes. It proves more accurate than a similar rectilinear mesh in terms of geometrical fit, and offers significant savings in processing time and memory use over a standard wave-based model. The new hybrid mesh also has the potential for improved real-world room boundary simulations through the inclusion of additional mixed modeling algorithms

Acoustic modeling using the digital waveguide mesh

The digital waveguide mesh has been an active area of music acoustics research for over ten years. Although founded in 1-D digital waveguide modeling, the principles on which it is based are not new to researchers grounded in numerical simulation, FDTD methods, electromagnetic simulation, etc. This article has attempted to provide a considerable review of how the DWM has been applied to acoustic modeling and sound synthesis problems, including new 2-D object synthesis and an overview of recent research activities in articulatory vocal tract modeling, RIR synthesis, and reverberation simulation. The extensive, although not by any means exhaustive, list of references indicates that though the DWM may have parallels in other disciplines, it still offers something new in the field of acoustic simulation and sound synth

Modelling body vibration and sound radiation of a modified kantele

Tässä työssä mallinnetaan 15-kielisen kanteleen kopan värähtelyä ja säteilyä elementtimenetelmän avulla. Kahta perinteistä kopan rakennetta, laatikkokanteletta ja lautakanteletta, verrataan muunneltuun rakenteeseen, jossa kopan ja kannen välillä on ilmarako. Tämä rakenne, jota kutsutaan myös nimellä vapaareuna-erillispohjarakenne, mahdollistaa kannen vapaan värähtelyn. Lisäksi pohjan ja kannen sulkemalla ilmatilalla on omat värähtelymuotonsa. Tämä muunnellun kanteleen on osoitettu olevan äänekkäämpi kuin perinteiset kanteleet. Tässä työssä osoitetaan, että muunnellussa kanteleessa yhdistyvät sekä kannen että ilmatilan värähtelymuodot. Siksi muunnellulla kanteleella on suurempi värähtelymuototiheys kuin perinteisillä kanteleilla. Muunneltu kantele on myös ympärisäteilevämpi, sillä ilmatilan värähtelymuodot kytkeytyvät kopan värähtelyihin. Tästä seuraa, että muunnellun kanteleen säteilytehokkuus on suurempi, kun ilmarako on pieni (1-3 mm).In this thesis, the vibrational modes and radiation of the body of a 15-string instrument called the kantele are modeled using the finite element method. Two traditional body structures, the top-plate kantele and the box kantele, are compared to a modified kantele with an air gap separating the top and the back plate. The modified structure allows the kantele top plate to vibrate freely. In addition, together the top and back plate create an enclosed air mass that has its own vibrational modes. The modified kantele has previously been shown to be louder than the traditional top plate kantele. In this thesis, it is shown that the modified kantele includes vibrational modes of both the freely vibrating top plate and the enclosed air. Thus, it has a higher mode density than the traditional kanteles. Because of the coupling of the enclosed air modes to the body, the modified kantele radiates more omni-directionally than the traditional kanteles. Consequently, the modified kantele has a higher radiation efficiency than the traditional kanteles when the size of the air gap is small (1-3 mm)

Spatially distributed computational modeling of a nonlinear vibrating string

Värähtelevän kielen epälineaarinen käyttäytyminen saa monissa kielisoittimissa aikaan soittimelle luonteenomaisen ja helposti tunnistettavan äänen. Laadukkaan kielisoitinsynteesin vuoksi onkin tärkeää, että nykyaikaiset äänisynteesimenetelmät ottavat huomioon myös kielten epälineaarisuudet. Tässä diplomityössä esitellään kaksi uutta synteesimenetelmää, jotka fysikaalisen mallinnuksen avulla simuloivat epälineaarisia näpättyjä kieliä paikkajakautuneesti, keskittyen jännitysmodulaation tuottamiin epälineaarisuuksiin. Toinen menetelmistä käyttää hajautettuja murtoviivesuotimia digitaalisen aaltojohtomallin viivesilmukan pituuden ajonaikaisessa virittämisessä, kun taas toinen hyödyntää murtoviivesuotimia äärelliseen erotukseen pohjautuvan mallin aikaresoluution muuttamisessa ajon aikana. Jännitysmodulaation suuruus arvioidaan kummankin mallin tapauksessa jokaisella aika-askeleella kielen pidentymästä. Molempien mallien simulaatiotulokset esitellään ja niitä verrataan toisiinsa sekä myös mitattuihin arvoihin. Epälineaarisen aaltojohtomallin avulla on toteutettu reaaliaikainen kantelemalli.Nonlinearities in string instruments are responsible for several interesting acoustical features, resulting in characteristic and easily recognizable tones. For this reason, modern synthesis models have to be capable of modeling this nonlinear behavior, when high quality results are desired. This thesis presents two novel physical modeling algorithms for simulating the tension modulation nonlinearity in plucked strings in a spatially distributed manner. The first method uses fractional delay filters within a digital waveguide structure, allowing the length of the string to be modulated during run time. The second method uses a nonlinear finite difference approach, where the string state is approximated between sampling instants also using fractional delay filters, thus allowing run-time modulation of the temporal sampling location. The magnitude of the tension modulation is evaluated from the elongation of the string at every time step in both cases. Simulation results of the two models are presented and compared. Real-time sound synthesis of the kantele, a traditional Finnish plucked-string instrument with strong effect of tension modulation, has been implemented using the nonlinear digital waveguide algorithm

Analysis and parametric synthesis of the piano sound

Tässä työssä tutkitaan pianon äänentuottomekanismia sekä akustisia ominaisuuksia. Tarkoituksena on luoda lähtökohdat pianon äänen parametriselle mallintamiselle. Lisäksi tutkitaan pianon äänen tärkeimpiä ominaisuuksia, kuten epäharmonisuutta, osaäänesten monimutkaista vaimenemisprosessia, kaikupohjan ja pedaalin ominaisuuksia sekä näiden tekijöiden vaikutuksia ääneen. Flyygelin ja pystypianon eroja tarkastellaan lyhyesti. Koska digitaalinen aaltojohtomallinnus tarjoaa parhaat lähtökohdat fysikaaliseen soitinmallinnukseen, tämä työ pohjautuu tähän tekniikkaan. Digitaalisen aaltojohtomallinnuksen pääpiirteet esitellään, kuten myös pianon kannalta olennaisimmat mallinnukseen liittyvät asiat. Lisäksi esitellään uusi tekniikka häviösuotimen suunnittelua varten, sekä annetaan muutama esimerkki käytännön suodinsuunnittelusta tällä tekniikalla. Tämän lisäksi tarkastellaan kaikupedaalin mallintamista sekä suoritetaan signaalianalyysi tehokkaan mallinnusalgoritmin löytämiseksi. Analysoitavat signaalit on äänitetty kahdessa äänityssessiossa vuoden 2005 aikana.In this thesis, an overview of the sound production mechanism of the piano is given. The acoustical properties of the instrument are studied in order to make a baseline for a physical and parametric model for the piano. In addition, the most important features of the piano sound, such as inharmonicity, the complicated decay process of the tones and the properties of the soundboard and the pedals, are investigated. The differences between the grand piano and the upright piano are considered in brief. As the digital waveguide technique is the most feasible physics-based sound synthesis technique at the moment, the synthesis procedure that is followed in this thesis is based on this technique. An overview of the main aspects of this synthesis scheme is given, and the most important modeling issues are taken into account from the piano sound synthesis point of view. A novel filter design technique for modeling the losses occurring in the piano sound is presented with some practical design examples. In addition, the modeling of the sustain pedal is discussed and signal analysis is performed in order to gather information for the synthetic sustain pedal algorithm. The analyzed signals are obtained from two recording sessions which were carried out in two parts during the year 2005

Magnetic suspension and vibration control of flexible structures for non-contact processing

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2000.Includes bibliographical references (p. 365-372).This thesis presents the design, analysis, and experimental testing of systems for noncontact suspension and control of flexible structures. Our particular focus is on the use of such suspensions in manufacturing processes which can be facilitated by the ability to control workpiece motion without contact. This can be of significant utility in processes such as coating, painting, heat treating, and web handling. We develop a novel approach for the control of such non-contact suspensions through what we term sensor averaging and actuator averaging. The difficult stability and robustness problems imposed by the flexible dynamics of the workpiece can be overcome by taking a properly-weighted average of the outputs of a distributed array of N motion sensors (sensor averaging), and/or by applying a properly-weighted distributed array of M forces (actuator averaging) to the workpiece. The theory for these dual techniques is developed in detail in the thesis. These approaches are shown to be independent of the specific boundary conditions or the longitudinal dimensions of the workpiece. These approaches are thus generally applicable to a wide range of structural control problems. We present both analytical and numerical analyses of the structural dynamics for typical flexible workpieces such as strings, beams, membranes, and plates. The analyses include axial translation of the workpiece. We have experimentally demonstrated the utility of our theory by application in the successful magnetic suspension of a 3 m long, 6.35 mm diameter, 0.89 mm wall thickness steel tube with varying boundary conditions. This is a very challenging problem due to the extremely light damping of the modes (< 0.001 with free ends). The experiment uses a set of 8 sensors and 8 actuators to measure and control the motion of the tube in the two lateral degrees of freedom. We present the details of the developed electromagnetic actuators, position sensors, modeling of the structural dynamics, the relevant vibration control techniques, and develop the associated theory for choosing sensor and actuator locations. Our results experimentally confirm the value of our averaging techniques, and suggest the wide future application of these ideas in industrial processes which require non-contact handling of workpieces.by Ming-chih Weng.Ph.D