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

Modeling and real-time synthesis of the kantele using distributed tension modulation

ABSTRACT Nonlinear behavior of a vibrating string is responsible for acoustical features in some plucked-string instruments, resulting in a characteristic and easily recognizable tone. That is also the case for the Finnish kantele, a traditional plucked-string instrument used in folk music. Earlier works have analyzed the general acoustic properties of the kantele and discussed related sound synthesis techniques. In this study, a novel modeling and sound synthesis method for simulating nonlinear string vibrations with spatially distributed tension modulation is presented. The modeling is conducted through a Digital Waveguide (DWG) approach, using controllable fractional delay elements in implementing the distributed tension modulation nonlinearity. The elongation of the vibrating string is estimated and the result is used in tuning the fractional delay values accordingly. Because of the spatially distributed nature of the approach, control of the string model parameters and observation of its behavior can be implemented at any point along it, in contrast to prior digital waveguide string models. This new approach is applied in constructing a physical model of a five-string kantele. Real-time sound synthesis is implemented using an efficient, block-based modeling tool, the BlockCompiler

Real-time physical model of an Aeolian harp

A real-time physical sound synthesis model of an Aeolian harp is presented. The model uses semi- empirical fluid dynamics equations to inform its operation, providing suitable parameters for users to interact. A basic wind model is included as well as an interface allowing user adjustable param- eters. Sounds generated by the model were subject to objective measurements against real-world recordings, which showed that many of the physical properties of the harp were replicated in our model, but a possible link between harmonics and vibration amplitude was not. A perceptual test was performed, where participants were asked to rate sounds in terms of how plausible they were in comparison with spectral modelling synthesis and recorded Aeolian Harp samples. Evaluation showed that our model performed as well as an alternative non-physical synthesis method, but was not as authentic as actual recorded samples

Efficient synthesis of tension modulation in strings and membranes based on energy estimation

String and membrane vibrations cannot be considered as linear above a certain amplitude due to the variation in string or membrane tension. A relevant special case is when the tension is spatially constant and varies in time only in dependence of the overall string length or membrane surface. The most apparent perceptual effect of this tension modulation phenomenon is the exponential decay of pitch in time. Pitch glides due to tension modulation are an important timbral characteristic of several musical instruments, including the electric guitar and tom-tom drum, and many ethnic instruments. This paper presents a unified formulation to the tension modulation problem for onedimensional (1-D) (string) and two-dimensional (2-D) (membrane) cases. In addition, it shows that the short-time average of the tension variation, which is responsible for pitch glides, is approximately proportional to the system energy. This proportionality allows the efficient physics-based sound synthesis of pitch glides. The proposed models require only slightly more computational resources than linear models as opposed to earlier tension-modulated models of higher complexity

Perception of attributes in real and synthetic string instrument sounds

This thesis explores the perceptual features of natural and synthetic string instrument sounds. The contributions are in formal listening experiments on a variety of features in musical sounds that have not been studied in detail previously. The effects of inharmonicity on timbre and pitch have been measured. The results indicate that the implementation of inharmonicity is not always necessary. The timbre effect is more salient in natural instruments, but for high tones a pitch difference may also be detected. Guidelines were given for compensation of the pitch effect. A perceptual study of the decaying parameters showed that large deviations from the reference value are tolerated perceptually. The studies on the audibility of initial pitch glides and dual-polarization effects provides practical knowledge that helps in the implementation of these features in digital sound synthesis. Related to expression rather than basic string behavior, the study on perception-based control of the vibrato parameters has a sligthly different background. However, all of the studied features are more or less player-controlled by different ways of plucking the string or pressing the key. The main objective of the thesis is to find answers to current problems in digital sound synthesis, such as parameter quantization. Another aim is to gain more general understanding of how we perceive musical sounds.reviewe