Download POWERWAVE: a high performance Single Chip Interpolating Wavetable Synthesizer In this paper we introduce the single chip implementation of a 16 voices wavetable synthesizer. All digital functions (control and waveform generation) are contained in a single platform FPGA chip (Xilinx Virtex 2 Pro). Only the digital to analog conversion is done by a standard 96 kHz audio DAC (AD 1785). In the first version the synthesizer is controlled via standard RS 232 interface.
Download Estimating the amplitude of the cubic difference tone using a third order adaptive Volterra Filter Design method of a nonlinear filter to estimate the amplitudes of cubic difference tones is presented. To this end, a third-order Volterra filter is used to model the nonlinearity of our auditory system, and the filter coefficients are obtained using an adaptive process. The results show the filtered outputs follow very closely the experimental data as the intensity levels and the frequencies of inputs vary especially when the frequency separation between the two primary tones is not large.
Download ACOUSTIC SIGNAL PROCESSING FOR NEXT-GENERATION HUMAN/MACHINE INTERFACES In this paper, we first define the scenario of a generic acoustic human/machine interface and then formulate the according fundamental signal processing problems. For signal reproduction, the requirements for ideal solutions are stated and some examples for the state of the technology are briefly reviewed. For signal acquisition, the fundamental problems ask for acoustic echo cancellation, desired source extraction, and source localization. After illustrating to which extent acoustic echo cancellation is already a solved problem, we present recent results for separation, dereverberation and localization of multiple source signals. As an underlying motivation for this synoptic treatment, we demonstrate that the considered subproblems (except localization) can be directly interpreted as signal separation or system identification problems with varying degrees of difficulty, which in turn determines the effectiveness of the known solutions.
Download Discretization of the '59 Fender Bassman Tone Stack The market for digital modeling guitar amplifiers requires that the digital models behave like the physical prototypes. A component of the iconic Fender Bassman guitar amplifier, the tone stack circuit, filters the sound of the electric guitar in a unique and complex way. The controls are not orthogonal, resulting in complicated filter coefficient trajectories as the controls are varied. Because of its electrical simplicity, the tone stack is analyzed symbolically in this work, and digital filter coefficients are derived in closed form. Adhering to the technique of virtual analog, this procedure results in a filter that responds to user controls in exactly the same way as the analog prototype. The general expressions for the continuous-time and discrete-time filter coefficients are given, and the frequency responses are compared for the component values of the Fender ’59 Bassman. These expressions are useful implementation and verification of implementations such as the wave digital filter.
Download On the Use of Volterra Series for Efficient Real-Time Simulations of Weakly Nonlinear Analog Audio Devices: Application to the Moog Ladder Filter In this paper, we show how the formalism of the Volterra series can be used to represent the nonlinear Moog ladder filter. The analog circuit is analyzed to produce a set of governing differential equations. The Volterra kernels of this system are solved from simple algebraic equations. They define an exact decomposition of the system. An identification procedure leads to structures composed of linear filters, sums and instantaneous products of signals. Finally, a discrete-time realization of the truncated series, which guarantees no aliasing, is performed.
Download Robust Design of Very High-Order Allpass Dispersion Filters A nonparametric allpass filter design method is presented for matching a desired group delay as a function of frequency. The technique is useful in physical modeling synthesis of musical instruments and emulation of audio effects devices exhibiting dispersive wave propagation. While current group delay filter design methods suffer from numerical difficulties except at low filter orders, the technique presented here is numerically robust, producing an allpass filter in cascaded biquad form, and with the filter poles following a smooth loop within the unit circle. The technique was inspired by the observation that a pole-zero pair arranged in allpass form contributes exactly 2π radians to the integral of group delay around the unit circle, regardless of the (stable) pole location. To match a given group delay characteristic, the method divides the frequency axis into sections containing 2π total area under the desired group-delay curve, and assigns a polezero allpass pair to each. In this way, the method incorporates an order selection technique, and by adding a pure delay to the desired group delay, allows the trading of increased filter order for improved fit to the frequency-dependent group delay. Design examples are given for modeling the group delay of a dispersive string (such as a piano string), and a dispersive spring, such as in a spring reverberator.
Download Consistency of Timbre Patterns in Expressive Music Performance Musical interpretation is an intricate process due to the interaction of the musician’s gesture and the physical possibilities of the instrument. From a perceptual point of view, these elements induce variations in rhythm, acoustical energy and timbre. This study aims at showing the importance of timbre variations as an important attribute of musical interpretation. For this purpose, a general protocol aiming at emphasizing specific timbre patterns from the analysis of recorded musical sequences is proposed. An example of the results obtained by analyzing clarinet sequences is presented, showing stable timbre variations and their correlations with both rhythm and energy deviations.
Download Real-Time Detection of Finger Picking Musical Structures MIDIME is a software architecture that houses improvisational agents that react to MIDI messages from a finger-picked guitar. They operate in a pipeline whose first stage converts MIDI messages to a map of the state of instrument strings over time, and whose second stage selects rhythmic, modal, chordal, and melodic interpretations from the superposition of interpretations latent in the first stage. These interpretations are nondeterministic, not because of any arbitrary injection of randomness by an algorithm, but because guitar playing is nondeterministic. Variations in timing, tuning, picking intensity, string damping, and accidental or intensional grace notes can affect the selections of this second stage. The selections open to the second stage, as well as the third stage that matches second stage selections to a stored library of composition fragments, reflect the superposition of possible perceptions and interpretations of a piece of music. This paper concentrates on these working analytical stages of MIDIME. It also outlines plans for using the genetic algorithm to develop improvisational agents in the final pipeline stage.
Download Using Visual Textures for Sonic Textures Production and Control This work takes place in the framework of a global research on the synthesis of sonic textures and its control through a gesturebased interaction in a musical practice. In this paper we present different strategies to link visual and sonic textures using similar synthesis processes; theoretical considerations underlying to this problematic are firstly exposed and several personal realizations, illustrating different approaches to design a gesturally controlled audio-visual system, are then described.
Download Graphic Equalizer Design Using Higher-Order Recursive Filters A straight-forward design of graphic equalizers with minimumphase behavior based on recently developed higher-order bandshelving filters is presented. Due to the high filter order, the gain in one band is almost completely independent from the gain in the other bands. Although no special care will be taken to design filters with complementary edges except for a suitable definition of the cut-off frequencies, the resulting amplitude deviation in the transitional region between the bands will be sufficiently low for many applications.