Download Notes on Model-Based Non-Sationary Sinusoid Estimation Methods Using Derivatives
This paper reviews the derivative method and explores its capacity for estimating time-varying sinusoids of complicated parameter variations. The method is reformulated on a generalized signal model. We show that under certain arrangements the estimation task becomes solving a linear system, whose coefficients can be computed from discrete samples using an integration-by-parts technique. Previous derivative and reassignment methods are shown to be special cases of this generic method. We include a discussion on the continuity criterion of window design for the derivative method. The effectiveness of the method and the window design criterion are confirmed by test results. We also show that, thanks to the generalization, off-model sinusoids can be approximated by the derivative method with a sufficiently flexible model setting.
Download A Frequency Domain Adaptive Algorithm for Wave Separation
We propose a frequency domain adaptive algorithm for wave separation in wind instruments. Forward and backward travelling waves are obtained from the signals acquired by two microphones placed along the tube, while the separation filter is adapted from the information given by a third microphone. Working in the frequency domain has a series of advantages, among which are the ease of design of the propagation filter and its differentiation with respect to its parameters. Although the adaptive algorithm was developed as a first step for the estimation of playing parameters in wind instruments it can also be used, without any modifications, for other applications such as in-air direction of arrival (DOA) estimation. Preliminary results on these applications will also be presented.
Download Towards Morphological Sound Description using segmental models
We present an approach to model the temporal evolution of audio descriptors using Segmental Models (SMs). This method yields a signal segmentation into a sequence of primitives, constituted by a set of user-defined trajectories . This allows one to consider specific primitive shapes, model their duration and to take into account the time dependence between successive signal frames, contrary to standard Hidden Markov Models. We applied this approach to a database of violin playing. Various types of glissando and dynamics variations were specifically recorded. The results show that our approach using Segmental Models provides a segmentation that can be easily interpreted. Quantitatively, the Segmental Models performed better than standard implementation of Hidden Markov Models.
Download Score based real-time performance with a virtual violin
This paper describes the implementation of a violin physical model tied with the control of music scores to enable the real-time performance of music pieces. The violin model is made of four strings, which allows the performance of double stops, chords and specific resonant effects that can be encountered in violin playing. A graphic tablet is used to control the bowing parameters and to trigger automatically note events contained in a specifically formatted MIDI file. The automatic pitch change helps reducing the violin playing complexity and enables the user to focus on sound shaping and phrasing. The device can be used for pure sound synthesis purposes as well as for experiments related to violinists’ sound control. However, the simplified interface for sound and score events is particularly suitable for non violinists wishing to explore expressive capabilities of the instrument and to experience specific features of violin playing.
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 Energy and Accuracy Issues in Numerical Simulations of a Non-linear Impact model
A physically-based impact model – already known and exploited in the field of sound synthesis – is studied using both analytical tools and numerical simulations. It is shown that, for some regions of the parameter space, the trajectories of discretized systems may drift from analytically-derived curves. Some methods, based on enforcing numerical energy consistency, are suggested to improve the accuracy and stability of discrete-time systems.
Download Low-order allpass Interpolated Delay Loops
This paper presents empirical and theoretical results for a delay line cascaded with a second-order allpass filter in a feedback loop. Though such a structure has been used for years to model stiff vibrating strings, the complete range of behavior of such a structure has not been fully described and analyzed. As shown in this paper, in addition to the desired behavior of providing a frequencydependent delay line length, other phenomena may occur, such as “beating” or “mode splitting.” Associated analysis simulation results are presented.
Download Rhythm-Synchronized Effects Control with Digital Modulation and Bezier Splines
This paper discusses details related to the automatic control of effects parameters. Specifically, it examines control of audio effects when synchronized with a musical piece’s rhythm. Synchronization is achieved by having control data that is periodic with the bar-length. The need for continuity in the control data is also discussed. This concept is introduced in terms of modulation techniques known as ASK and CPFSK. This is expanded upon with a discussion of a curve drawing technique that is common to computer graphics.
Download Binaural HRTF-based Spatialization: New Approaches and Implementation
New approaches to Head Related Transfer Function (HRTF) based artificial spatialisation of audio are presented and discussed in this paper. A brief summary of the topic of audio spatialisation and HRTF interpolation is offered, followed by an appraisal of the existing minimum phase HRTF interpolation method. Novel alternatives are then suggested which essentially approach the problem of phase interpolation more directly. The first technique, based on magnitude interpolation and phase truncation, aims to use the empirical HRTFs without the need for complex data preparation or manipulation, while minimizing any approximations that may be introduced by data transformations. A second approach augments a functionally based phase model with low frequency non-linear frequency scaling based on the empirical HRTFs, allowing a more accurate phase representation of the more relevant lower frequency end of the spectrum. This more complex approach is deconstructed from an implementation point of view. Testing of both algorithms is then presented, which highlights their success, and favorable performance over minimum phase plus delay methods.