Download Extensions and Applications of Modal Dispersive Filters Dispersive delay and comb filters, implemented as a parallel sum of high-Q mode filters tuned to provide a desired frequency-dependent delay characteristic, have advantages over dispersive filters that are implemented using cascade or frequency-domain architectures. Here we present techniques for designing the modal filter parameters for music and audio applications. Through examples, we show that this parallel structure is conducive to interactive and time-varying modifications, and we introduce extensions to the basic model.
Download Nonlinear Strings based on Masses and Springs Due to advances in computational power, physical modelling for sound synthesis has gained an increased popularity over the past decades. Although much work has been done to accurately simulate existing physical systems, much less work exists on the use of physical modelling simply for the sake of creating sonically interesting sounds. This work presents a mass-spring network, inspired by existing models of the physical string. Masses have 2 translational degrees of freedom (DoF), and the springs have an additional equilibrium separation term, which together result in highly nonlinear effects. The main aim of this work is to create sonically interesting sounds while retaining some of the natural qualities of the physical string, as opposed to accurately simulating it. Although the implementation exhibits chaotic behaviour for certain choices of parameters, the presented system can create sonically interesting timbres, including nonlinear pitch glides and ‘wobbles’.
Download A perceptually inspired generative model of rigid-body contact sounds Contact between rigid-body objects produces a diversity of impact and friction sounds. These sounds can be synthesized with detailed simulations of the motion, vibration and sound radiation of the objects, but such synthesis is computationally expensive and prohibitively slow for many applications. Moreover, detailed physical simulations may not be necessary for perceptually compelling synthesis; humans infer ecologically relevant causes of sound, such as material categories, but not with arbitrary precision. We present a generative model of impact sounds which summarizes the effect of physical variables on acoustic features via statistical distributions fit to empirical measurements of object acoustics. Perceptual experiments show that sampling from these distributions allows efficient synthesis of realistic impact and scraping sounds that convey material, mass, and motion.
Download Efficient Simulation of the Bowed String in Modal Form The motion of a bowed string is a typical nonlinear phenomenon resulting from a friction force via interaction with the bow. The system can be described using suitable differential equations. Implicit numerical discretisation methods are known to yield energy consistent algorithms, essential to ensure stability of the timestepping schemes. However, reliance on iterative nonlinear root finders carries significant implementation issues. This paper explores a method recently developed which allows nonlinear systems of ordinary differential equations to be solved non-iteratively. Case studies of a mass-spring system and an ideal string coupled with a bow are investigated. Finally, a stiff string with loss is also considered. Combining semi-discretisation and a modal approach results in an algorithm yielding faster than real-time simulation of typical musical strings.
Download Latent Force Models for Sound: Learning Modal Synthesis Parameters and Excitation Functions from Audio Recordings Latent force models are a Bayesian learning technique that combine physical knowledge with dimensionality reduction — sets of coupled differential equations are modelled via shared dependence on a low-dimensional latent space. Analogously, modal sound synthesis is a technique that links physical knowledge about the vibration of objects to acoustic phenomena that can be observed in data. We apply latent force modelling to sinusoidal models of audio recordings, simultaneously inferring modal synthesis parameters (stiffness and damping) and the excitation or contact force required to reproduce the behaviour of the observed vibrational modes. Exposing this latent excitation function to the user constitutes a controllable synthesis method that runs in real time and enables sound morphing through interpolation of learnt parameters.
Download Physically Informed Synthesis of Jackhammer Tool Impact Sounds This paper introduces a sound synthesis method for jackhammer tool impact sounds. The model is based on parallel waveguide models for longitudinal and transversal vibrations. The longitudinal sounds are produced using a comb filter that is tuned to match the longitudinal resonances of a steel bar. The dispersive transversal vibrations are produced using a comb filter which has a cascade of first-order allpass filters and time-varying feedback coefficient. The synthesis model is driven by an input generator unit that produces a train of Hann pulses at predetermined time-intervals. Each pulse has its amplitude modified slightly by a random process. For increased realism each impact is followed by a number of repetitive impacts with variable amplitude and time difference according to the initial pulse. The sound output of the model is realized by mixing both transversal and longitudinal signals and the effect is finalized by an equalizer.
Download Guaranteed-passive simulation of an electro-mechanical piano: a port-Hamiltonian approach This paper deals with the time-domain simulation of a simplified electro-mechanical piano. The physical model is composed of a hammer (nonlinear component), a cantilever beam (damped linear resonator) and a pickup (nonlinear transducer). In order to ensure stable simulations, a method is proposed, which preserves passivity, namely, the conservative and dissipative properties of the physical system. This issue is addressed in 3 steps. First, each physical component is described by a passive input-output system, which is recast in the port-Hamiltonian framework. In particular, a passive finite dimensional model of the Euler-Bernoulli beam is derived, based on a standard modal decomposition. Second, these components are connected, providing a nonlinear finite dimensional port-Hamiltonian system. Third, a numerical method is proposed, which preserves the power balance and passivity. Numerical results are presented and analyzed.
Download 10 criteria for evaluating physical modelling schemes for music creation The success recently encountered by physically-based modeling (or model-based approaches) for music should not mask the deep challenges that remain in this area. This article first proposes an overview of the various goals that researchers and musicians, respectively operating from scientific and end-user perspectives, may pursue. Among these goals, those recently proposed or particularly critical for the coming years of research are highlighted. The article then introduces ten criteria that summarize the main features an optimal physically-based modeling scheme or language should present. With respect to these, it proposes an evaluation of the major approaches to physically-based modeling. Key words: goals of the physically-based approach to sound synthesis and music creation, languages and schemes, enduser needs, perception, evaluation criteria, bibliographic overview.
Download Energy-based synthesis of tension modulation in strings Above a certain amplitude, the string vibration becomes nonlinear due to the variation of tension. An important special case is when the tension varies with time but spatially uniform along the string. The most important effect of this tension modulation is the exponential decay of the pitch (pitch glide). In the case of nonrigid string termination, the generation of double frequency terms and the excitation of missing modes also occurs, but this is perceptually less relevant for most of the cases. Several modeling strategies have been developed for tension modulated strings. However, their computational complexity is significantly higher compared to linear string models. This paper proposes efficient techniques for modeling the quasistatic part (short-time average) of the tension variation that gives rise to the most relevant pitch glide effect. The modeling is based on the linear relationship between the energy of the string and quasistatic tension variation. When this feature is added to linear string models, the computational complexity is increased by a negligible amount, leading to significant savings compared to earlier tension modulated string models.
Download Nonlinear Allpass Ladder Filters in FAUST Passive nonlinear filters provide a rich source of evolving spectra for sound synthesis. This paper describes a nonlinear allpass filter of arbitrary order based on the normalized ladder filter. It is expressed in FAUST recursively in only two statements. Toward the synthesis of cymbals and gongs, it was used to make nonlinear waveguide meshes and feedback-delay-network reverberators.