Download Computation of Nonlinear Filter Networks Containing Delay-Free Paths A method for solving filter networks made of linear and nonlinear filters is presented. The method is valid independently of the presence of delay-free paths in the network, provided that the nonlinearities in the system respect certain (weak) hypotheses verified by a wide class of real components: in particular, that the contribution to the output due to the memory of the nonlinear blocks can be extracted from each nonlinearity separately. The method translates into a general procedure for computing the filter network, hence it can serve as a testbed for offline testing of complex audio systems and as a starting point toward further code optimizations aimed at achieving real time.
Download Multimodal Interfaces for Expressive Sound Control This paper introduces research issues on multimodal interaction and interfaces for expressive sound control. We introduce Multisensory Integrated Expressive Environments (MIEEs) as a framework for Mixed Reality applications in the performing arts. Paradigmatic contexts for applications of MIEEs are multimedia concerts, interactive dance / music / video installations, interactive museum exhibitions, distributed cooperative environments for theatre and artistic expression. MIEEs are user-centred systems able to interpret the high-level information conveyed by performers through their expressive gestures and to establish an effective multisensory experience taking into account expressive, emotional, affective content. The lecture discusses some main issues for MIEEs and presents the EyesWeb (www.eyesweb.org) open software platform which has been recently redesigned (version 4) in order to better address MIEE requirements. Short live demonstrations are also presented.
Download A New Score Function for Joint Evaluation of Multiple F0 Hypotheses This article is concerned with the estimation of the fundamental frequencies of the quasiharmonic sources in polyphonic signals for the case that the number of sources is known. We propose a new method for jointly evaluating multiple F0 hypotheses based on three physical principles: harmonicity, spectral smoothness and synchronous amplitude evolution within a single source. Given the observed spectrum a set of F0 candidates is listed and for any hypothetical combination among the candidates the corresponding hypothetical partial sequences are derived. Hypothetical partial sequences are then evaluated using a score function formulating the guiding principles in mathematical forms. The algorithm has been tested on a large collection of arti cially mixed polyphonic samples and the encouraging results demonstrate the competitive performance of the proposed method.
Download Piano Transcription Using Pattern Recognition: Aspects on Parameter Extraction A method for chord recognition for piano transcription has been previously presented by the authors. The method presents some limitations due to errors in parameter extraction carried out during the training process. Parameter extraction of piano notes is not as straightforward as sometimes can be thought. Spectral components detection is necessary but not enough to obtain accurately some note parameters. The inharmonicity coefficient B is one of the parameters that are difficult to evaluate. The obtained value of B is different for every partial used to calculate it, and sometimes, these differences are high. Tuning with respect to tempered scale is another important note parameter. The problems arise when we try to measure the tuning of a note belonging to octaves 0 or 1, because the fundamental is radiated by the soundboard with a very low level and, therefore, it is not captured by the recording microphone and cannot be measured. A method to avoid these drawbacks is presented in this paper, including an explanation of the basis.
Download Modal-Type Synthesis Techniques for Nonlinear Strings with an Energy Conservation Property There has recently been increased interest in the modelling of string vibration under large amplitude conditions, for sound synthesis purposes. A simple nonlinear model is given by the KirchhoffCarrier equation, which can be thought of as a generalization of the wave equation to the case for which the string tension is “modulated” by variations in the length of the string under deformation. Finite difference schemes are one means of approach for the simulation of nonlinear PDE systems; in this case, however, as the nonlinearity is spatially invariant, the solution may be broken down into sinusoidal components, much as in the linear case. More importantly, if time discretization is carried out in a particular way, it is possible to obtain a conserved energy in the numerical scheme, leading to a useful numerical stability guarantee, which can be difficult to obtain for strongly nonlinear systems. Numerical results are presented.
Download Practical Implementation of the 3D Tetrahedral TLM Method and Visualization of Room Acoustics This paper concerns the implementation of a 3D transmission line matrix (TLM) algorithm based on a tetrahedral mesh structure and visualization of room acoustics simulation. Although a well known method, TLM algorithms implemented in 3D are less commonly found in the literature. We have implemented the TLM method using a tetrahedral mesh of pressure nodes with transmission lines lying superimposed on nearest neighbour bonds of a tetrahedral atomic lattice. Results of simulations are compared with those of a standard 3D cartesian mesh and a 2D mesh implementation of TLM. An important feature is a useful graphics interface designed for user-friendly control of room acoustics simulation and visualization in arbitrary shaped rooms containing objects of arbitrary size and number. The paper includes brief discussions of results of using different techniques for modeling totally absorptive or partially absorptive boundaries.
Download Binaural source localization In binaural signals, interaural time differences (ITDs) and interaural level differences (ILDs) are two of the most important cues for the estimation of source azimuths, i.e. the localization of sources in the horizontal plane. For narrow band signals, according to the duplex theory, ITD is dominant at low frequencies and ILD is dominant at higher frequencies. Based on the STFT spectra of binaural signals, a method is proposed for the combined evaluation of ITD and ILD for each individual spectral coefficient. ITD and ILD are related to the azimuth through lookup models. Azimuth estimates based on ITD are more accurate but ambiguous at higher frequencies due to phase wrapping. The less accurate but unambiguous azimuth estimates based on ILDs are used in order to select the closest candidate azimuth estimates based on ITDs, effectively improving the azimuth estimation. The method corresponds well with the duplex theory and also handles the transition from low to high frequencies gracefully. The relations between the ITD and ILD and the azimuth are computed from a measured set of head related transfer functions (HRTFs), yielding azimuth lookup models. Based on a study of these models for different subjects, parametric azimuth lookup models are proposed. The parameters of these models can be optimized for an individual subject whose HRTFs have been measured. In addition, subject independent lookup models are proposed, parametrized only by the distance between the ears, effectively enabling source localization for subjects whose HRTFs have not been measured.
Download Semi-automatic Ambience Generation Ambiances are background recordings used in audiovisual productions to make listeners feel they are in places like a pub or a farm. Accessing to commercially available atmosphere libraries is a convenient alternative to sending teams to record ambiances yet they limit the creation in different ways. First, they are already mixed, which reduces the flexibility to add, remove individual sounds or change its panning. Secondly, the number of ambient libraries is limited. We propose a semi-automatic system for ambiance generation. The system creates ambiances on demand given text queries by fetching relevant sounds from a large sound effect database and importing them into a sequencer multitrack project. Ambiances of diverse nature can be created easily. Several controls are provided to the users to refine the type of samples and the sound arrangement.
Download Effect of Latency on Playing Accuracy of Two Gesture Controlled Continuous Sound Instruments Without Tactile Feedback The paper reports results from an experimental study quantifying how latency affects the playing accuracy of two continuous sound instruments. 11 subjects played a conventional Theremin and a virtual reality Theremin. Both instruments provided the user only audio feedback. The subjects performed two tasks under different instrument latencies. They attempted to match the pitch of the instrument to a sample pitch and they played along a short sample melody and a metronome. Both the sample sound and the instrument’s sound were recorded on different channels of a sound file. Later the pitch of the sounds was extracted and user performance analyzed. The results show that the time required to match a given pitch degrades about five times the introduced latency suggesting that the feedback latency cumulates over the whole task. Errors while playing along a sample melody increased 80% by average on the highest latency of 240ms. Latencies until 120ms increased the errors only slightly.
Download Real Time Modeling of Acoustic Propagation in Complex Environments In order to achieve high-quality audio-realistic rendering in complex environments, we need to determine all the acoustic paths that go from sources to receivers, due to specular reflections as well as diffraction phenomena. In this paper we propose a novel method for computing and auralizing the reflected as well as the diffracted field in 2.5D environments. The method is based on a preliminary geometric analysis of the mutual visibility of the environment reflectors. This allows us to compute on the fly all possible acoustic paths, as the information on sources and receivers becomes available. The construction of a beam tree, in fact, is here performed through a look-up of visibility information and the determination of acoustic paths is based on a lookup on the computed beam tree. We also show how to model diffraction using the same beam tree structure used for modeling reflection and transmission. In order to validate the method we conducted an acquisition campaign over a real environment and compared the results obtained with our real-time simulation system.