Oversampling for Nonlinear Waveshaping: Choosing the Right Filters

Abstract

An assessment of filters for classic oversampled audio waveshaping schemes is carried out in this paper, pursuing aliasing reduction. For this purpose, the quality measure of the Aweighted noise-to-mask ratio is computed for test tones covering the frequency range from 27.5 Hz to 4.186 kHz, sampled at 44.1 kHz, and processed at eight-times oversampling. All filters are designed to have their passband contained within a ±1 dB range and to display a minimum stopband attenuation value of 40 dB. Waveshaping of sinusoids via hard clipping is investigated: the spectral enrichment due to the discontinuities introduced by its nonlinear transfer function maximizes aliasing distortion. The obtained results suggest that linear interpolation equalized with a high shelving filter is a sufficiently good method for upsampling. Concerning decimation, the interpolated FIR, elliptic, and cascaded integrator-comb filters all improve the results with respect to the trivial case. Regarding performance, the cascaded integrator-comb filter is the only tested decimation filter that achieves perceptually sufficient aliasing suppression for the entire frequency range when combined with the linear interpolator.

Real-Time Guitar Amplifier Emulation with Deep Learning

“…However, while the aliasing is evident with a high-frequency sinusoidal input, no clear aliasing could be heard in the guitar and bass sounds processed through the models. If this becomes a problem, it is possible that aliasing suppression techniques, such as oversampling [40], could be applied during the neural network training, however, this is left for future work.…”

Antiderivative Antialiasing Techniques in Nonlinear Wave Digital Structures

“…The two antiparallel diodes are grouped together as a one-port nonlinear element placed at the root of the BCT structure and characterized by the explicit relation (27). In particular, first-order ADAA is employed by using (4) in conjunction with (28). Second-order ADAA instead uses (12) along with the first and secondorder antiderivatives (28) and (29).…”

“…In particular, first-order ADAA is employed by using (4) in conjunction with (28). Second-order ADAA instead uses (12) along with the first and secondorder antiderivatives (28) and (29). Moreover care must be taken when numerical ill-conditioning occurs, as specified in [30].…”

“…However increasing the sampling frequency may lead to computationally inefficient implementations that could violate real-time execution constraints. Hence alternative less expensive antialiasing methods are desirable, and many techniques have been proposed in the VA literature, dealing with discrete-time oscillators for subtractive synthesis [24,25], emulations of clipping stages used in overdrive or distortion circuits [26,27], and interpolation filters combined with decimation filters for nonlinear waveshaping [28].…”

An Audio Synthesis Framework Derived from Industrial Process Control

“…While this strategy is sufficient in practical cases to reduce aliasing to a great extent, it seems unnatural and detached from the PID control technique. Additionally, the computational complexity of this method scales up with an increase in the magnitude of oversampling (that may be required for the higher audio frequencies) and the order of the filter used [10].…”