Download Optimal Integer Order Approximation of Fractional Order Filters Fractional order filters have been studied since a long time,
along with their applications to many areas of physics and engineering. In particular, several solutions have been proposed in
order to approximate their frequency response with that of an ordinary filter. In this paper, we tackle this problem with a new approach: we solve analytically a simplified version of the problem
and we find the optimal placement of poles and zeros, giving a
mathematical proof and an error estimate. This solution shows improved performance compared to the current state of the art and is
suitable for real-time parametric control.
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.
Download A Quadric Surface Model of Vacuum Tubes for Virtual Analog Applications Despite the prevalence of modern audio technology, vacuum tube amplifiers continue to play a vital role in the music industry. For this reason, over the years, many different digital techniques have been introduced for accomplishing their emulation. In this paper, we propose a novel quadric surface model for tube simulations able to overcome the Cardarilli model in terms of efficiency whilst retaining comparable accuracy when grid current is negligible. After showing the model capability to well outline tubes starting from measurement data, we perform an efficiency comparison by implementing the considered tube models as nonlinear 3-port elements in the Wave Digital domain. We do this by taking into account the typical common-cathode gain stage employed in vacuum tube guitar amplifiers. The proposed model turns out to be characterized by a speedup of 4.6× with respect to the Cardarilli model, proving thus to be promising for real-time Virtual Analog applications.
Download Antiderivative Antialiasing with Frequency Compensation for Stateful Systems Employing nonlinear functions in audio DSP algorithms requires attention as they generally introduce aliasing. Among others, antiderivative antialiasing proved to be an effective method for static nonlinearities and gave rise to a number of variants, including our AA-IIR method. In this paper we introduce an improvement to AA-IIR that makes it suitable for use in stateful systems. Indeed, employing standard antiderivative antialiasing techniques in such systems alters their frequency response and may cause stability issues. Our method consists in cascading a digital filter after the AA-IIR block in order to fully compensate for unwanted delay and frequency-dependent effects. We study the conditions for such a digital filter to be stable itself and evaluate the method by applying it to the diode clipper circuit.