Download Efficient signal extrapolation by granulation and convolution with velvet noise Several methods are available nowadays to artificially extend the duration of a signal for audio restoration or creative music production purposes. The most common approaches include overlap-andadd (OLA) techniques, FFT-based methods, and linear predictive coding (LPC). In this work we describe a novel OLA algorithm based on convolution with velvet noise, in order to exploit its sparsity and spectrum flatness. The proposed method suppresses spectral coloration and achieves remarkable computational efficiency. Its issues are addressed and some design choices are explored. Experimental results are proposed and compared to a well-known FFT-based method.
Download Fast Approximation of the Lambert W Function for Virtual Analog Modelling When modelling circuits one has often to deal with equations containing both a linear and an exponential part. If only a single exponential term is present or predominant, exact or approximate closed-form solutions can be found in terms of the Lambert W function. In this paper, we propose reformulating such expressions in terms of the Wright Omega function when specific conditions are met that are customary in practical cases of interest. This eliminates the need to compute an exponential term at audio rate. Moreover, we propose simple and real-time suitable approximations of the Omega function. We apply our approach to a static and a dynamic nonlinear system, obtaining digital models that have high accuracy, low computational cost, and are stable in all conditions, making the proposed method suitable for virtual analog modelling of circuits containing semiconductor devices.
Download Analysis and Emulation of Early Digitally-Controlled Oscillators Based on the Walsh-Hadamard Transform Early analog synthesizer designs are very popular nowadays, and the discrete-time emulation of voltage-controlled oscillator (VCO) circuits is covered by a large number of virtual analog (VA) textbooks, papers and tutorials. One of the issues of well-known VCOs is their tuning instability and sensitivity to environmental conditions. For this reason, digitally-controlled oscillators were later introduced to provide stable tuning. Up to now, such designs have gained much less attention in the music processing literature. In this paper, we examine one of such designs, which is based on the Walsh-Hadamard transform. The concept was employed in the ARP Pro Soloist and in the Welson Syntex, among others. Some historical background is provided, along with a discussion on the principle, the actual implementation and a band-limited virtual analog derivation.
Download Arbitrary-Order IIR Antiderivative Antialiasing Nonlinear digital circuits and waveshaping are active areas of study,
specifically for what concerns numerical and aliasing issues. In
the past, an effective method was proposed to discretize nonlinear
static functions with reduced aliasing based on the antiderivative of
the nonlinear function. Such a method is based on the continuoustime convolution with an FIR antialiasing filter kernel, such as a
rectangular kernel. These kernels, however, are far from optimal
for the reduction of aliasing. In this paper we introduce the use
of arbitrary IIR rational transfer functions that allow a closer approximation of the ideal antialiasing filter, required in the fictitious continuous-time domain before sampling the nonlinear function output. These allow a higher degree of aliasing reduction and
can be flexibly adjusted to balance performance and computational
cost.