A tremendous number of techniques have been proposed to transfer artistic style from one image to another. In particular, techniques exploiting neural representation of data; from Convolutional Neural Networks to Generative Adversarial Networks. However, most of these techniques do not accurately account for the semantic information related to the objects present in both images or require a considerable training set. In this paper, we provide a data augmentation technique that is as faithful as possible to the style of the reference artist, while requiring as few training samples as possible, as artworks containing the same semantics of an artist are usually rare. Hence, this paper aims to improve the state-of-the-art by first applying semantic segmentation on both images to then transfer the style from the painting to a photo while preserving common semantic regions. The method is exemplified on Van Gogh’s paintings, shown to be challenging to segment.

In the last decades many efficient methods have been proposed to generate waveforms with reduced aliasing, proving this field quite mature. However, the introduction of Antiderivative Antialiasing (AA) methods for the reduction of aliasing in nonlinear discrete-time processing, can shed a new light on bandlimited oscillators and provide a general method for dealing with aliasing in arbitrary waveforms generation. In this work we will first bridge the gap between AA methods and bandlimited waveform generation, and then show the flexibility of the recently introduced AA-IIR method for dealing with both classical synthesizer waveforms and arbitrary wavetables. We will show how AA methods can be used for periodic and non-periodic waveform generation, and provide an innovative AA-IIR method able to compute alias-reduced version of any waveform with arbitrary antialiasing filter order, without the effort of computing ad hoc analytical expressions. Antialiasing performance is compared with other well known methods, showing the effectiveness of the approach.

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.

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 continuous-time 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.

The Moog ladder filter, which consists of four cascaded first-order ladder stages in a feedback loop, falls within the class of devices that have attracted greatest interest in virtual analog research. On one hand, this work confirms that the presence of exactly four stages in the original analog circuit is motivated by specific filter control issues and, on the other, that such a limitation can be overcome in the digital domain with relative ease. First, a continuous-time large-signal model is defined for a version of the circuit that is generalized to an arbitrary number of ladder stages. Then, the linear behavior of the filter around its natural operating point and the effect of control parameters on the resulting frequency response are studied in depth, to obtain exact analytical expressions for the position of poles in the transfer function and for the dc gain of the filter, as well as a parameterization strategy that is consistent for any number of ladder stages. A previously-introduced linear digital model of the device suggested by Smith is eventually generalized based on these general results, which remain, however, relevant and similarly applicable to other discretizations of the filter. The proposed model faithfully reproduces the linear behavior of the generalized device while providing sensible parametric control for any number of ladder stages.

One of the most critical aspects of virtual analog simulation of circuits for music production consists in accurate reproduction of their nonlinear behavior, yet this goal is in many cases difficult to achieve due to the presence of implicit differential equations in circuit models, since they naturally map to delay-free loops in the digital domain. This paper presents a novel and general method for non-iteratively implementing these loops in such a way that the linear response around a chosen operating point is preserved, the topology is minimally affected, and transformation of nonlinearities is not required. This technique is then applied to a generalized model of the Moog ladder filter, resulting in an implementation that outperforms its predecessors with only a modest computational load penalty. This digital version of the filter is shown to offer strong stability guarantees w.r.t. parameter variation, allows the extraction of different frequency response modes by simple mixing of individual ladder stage outputs, and is suitable for real-time sound synthesis and audio effects processing.

The Moog ladder structure is a well known filter used in musical sound synthesizers and in music production. Previously several digital models have attempted to imitate its nonlinear and self-oscillating characteristics. In this paper we derive a novel circuit-based model for the Moog filter and discretize it using the bilinear transform. The proposed nonlinear digital filter compares favorably against Huovilainen's model, which is the best previous white-box model for the Moog filter. The harmonic distortion characteristics of the proposed model match closely with those of a SPICE simulation. Furthermore, the novel model realistically enters the self-oscillation mode and maintains it. The proposed model requires only 12 more basic operations per output sample than Huovilainen's model, but includes the same number of nonlinear functions, which dominate the computational load. The novel nonlinear digital filter is applicable in virtual analog music synthesis and in musical audio effects processing.

A new family of wave-digital vacuum tube triode models is presented. These models are inspired by the triode model by Cardarilli , which provides realistic simulation of the triode's transconductance behavior, and hence high accuracy in saturation conditions. The triode is modeled as a single memoryless nonlinear three-port wave digital filter element in which the outgoing wave variables are computed by locally applying the monodimensional secant method to one or two port voltages, depending on whether the grid current effect is taken into account. The proposed algorithms were found to produce a richer static harmonic response, introducing comparable or less aliasing and requiring approximately 50% less CPU time than previous models. The proposed models are suitable for real-time virtual analog circuit simulation.

Wave digital filters (WDFs) allow for efficient real-time simulation of classic analog circuitry by DSP. This paper introduces two new nonenergic two-port WDF adaptors that allow mixing wave digital subnetworks adopting different polarity and sign conventions and extends the definitions of absorbed instantaneous and steady-state pseudopower to the case in which the active sign convention is used. This new knowledge is applied to a WDF triode tube amplifier model and it is shown to result in a more faithful reproduction of the simulated system than the previous model.