Real time tube guitar amplifier simulation using WebAudio

This paper presents a tube guitar amplifier simulation made with the WebAudio API, that reproduces the main parts of the Marshall JCM 800 amplifier schematics. Each stage of the real amp has been recreated (preamp, tone stack, reverb, power amp and speaker simulation, and we added an extra multiband EQ). The “classic rock” amp simulation we built has been used in real gigs and can be compared with some native amp simulation both in terms of latency, sound quality, dynamics and comfort of the guitar play. Unfortunately, as of today, low latency can be achieved only with certain configurations, due to audio driver limitations of current browsers on certain operating systems. The paper discusses the latency problems encountered with WebAudio, common traps, current limitations, and proposes some solutions. The final web based simulation has been compared with native recreations of the same amp model (including commercial products such as GuitarRig, the JCM800 amp included in GarageBand or the open source Guitarix amp sim that runs on Linux), and with a real amp: the Yamaha THR10 that comes with a model of a Marshall amp. We conducted both quantitative evaluations (measure of the “guitar-to-speaker” latency, group delay, frequency response analysis) and qualitative evaluations with real guitar players who compared, guitar in hands, the different simulations in terms of sound quality and dynamics, and more generally “how they feel playing guitar with these simulations”. The amp is open source1 and can be tested online2, even without a guitar (it comes with an audio player, dry guitar samples and a wave generator that can be used at input). The Web page contains links to the source code repository, tutorial videos and a complete report of the measures we made, with different configurations (various soundcard, operating system, browsers), that is summarized in this paper. Figure 1 shows the current GUI (with optional frequency analyzers and oscilloscopes we used to probe the signal at different stages of the simulation). Our initial goal was to evaluate the limits of the WebAudio API and see if it was possible to design a web based guitar amp simulator that could compete with native simulations

Real-time Digital Simulation of Guitar Amplifiers as Audio Effects

Práce se zabývá číslicovou simulací kytarových zesilovačů, jakož to nelineárních analogových hudebních efektů, v reálném čase. Hlavním cílem práce je návrh algoritmů, které by umožnily simulaci složitých systémů v reálném čase. Tyto algoritmy jsou prevážně založeny na automatizované DK-metodě a aproximaci nelineárních funkcí. Kvalita navržených algoritmů je stanovana pomocí poslechových testů.The work deals with the real-time digital simulation of guitar amplifiers considered as nonlinear analog audio effects. The main aim is to design algorithms which are able to simulate complex systems in real-time. These algorithms are mainly based on the automated DK-method and the approximation of nonlinear functions. Quality of the designed algorithms is evaluated using listening tests.

Deep Learning-Based Wave Digital Modeling of Rate-Dependent Hysteretic Nonlinearities for Virtual Analog Applications

Electromagnetic components greatly contribute to the peculiar timbre of analog audio gear. Indeed, distortion effects due to the nonlinear behavior of magnetic materials are known to play an important role in enriching the harmonic content of an audio signal. However, despite the abundant research that has been devoted to the characterization of nonlinearities in the context of virtual analog modeling over the years, the discrete-time simulation of circuits exhibiting rate-dependent hysteretic phenomena remains an open challenge. In this article, we present a novel data-driven approach for the wave digital modeling of rate-dependent hysteresis using recurrent neural networks (RNNs). Thanks to the modularity of wave digital filters, we are able to locally characterize the wave scattering relations of a hysteretic reluctance by encapsulating an RNN-based model into a single one-port wave digital block. Hence, we successfully apply the proposed methodology to the emulation of the output stage of a vacuum-tube guitar amplifier featuring a nonlinear transformer

Antiderivative antialiasing for memoryless nonlinearities

Aliasing is a commonly encountered problem in audio signal processing, particularly when memoryless nonlinearities are simulated in discrete time. A conventional remedy is to operate at an oversampled rate. A new aliasing reduction method is proposed here for discrete-time memoryless nonlinearities, which is suitable for operation at reduced oversampling rates. The method employs higher order antiderivatives of the nonlinear function used. The first-order form of the new method is equivalent to a technique proposed recently by Parker et al. Higher order extensions offer considerable improvement over the first antiderivative method, in terms of the signal-to-noise ratio. The proposed methods can be implemented with fewer operations than oversampling and are applicable to discrete-time modeling of a wide range of nonlinear analog systems.Peer reviewe

Dual Method Headphone Amplifier

Many high impedance headphones underperform their full potential when directly connected to the audio source. Amplifiers boost the audio signal and provide the headphones with sufficient power to ensure their maximum performance. The invention of transistors caused vacuum tube implementation to decline, leaving many audiophiles unsatisfied with the transistor’s sound signature. Vacuum tubes and transistors both amplify signals, however the distinct “tube sound” has vanished. We have designed and created a product where the user selectively switches between solid-state transistor and tube amplification to compare the sound signatures of each amplification method. The ability to switch between the solid-state and tube amplifiers creates the ability to achieve a more customized sound for individual songs and improve the user’s listening experience. This requires the design of two separate amplifiers and circuitry to switch back and forth between amplification methods without pausing the music or unplugging any device

Pultec EQP-1A Modeling with Wave Digital Filters

This thesis presents the development of a virtual analog model of the passive equal-izer section of the Pultec EQP-1A studio equalizer using Wave Digital Filters (WDF). The aim of the project was to provide an accurate and high performance open-source emulation of the circuitry and sound characteristics of the original hardware unit. The development process involved compiling the original unit’s schematics, gener-ating LTSpice simulations, and implementing the circuit in Python using the pywdf library and R-Type adaptors (a kind of adaptor used for modeling complex circuit junctions that cannot be classified as series or parallel). Since the R-Type adaptors greatly affected the performance of the model, the circuit was slightly modified to maintain its behavior without the need for R-Type adaptors. The frequency response of the Python prototype was compared to the LTSpice simulation showing that at sufficiently high sampling rates the error between the model and the simulations are minimal. The Python model was then ported to C++ using the JUCE framework and Chowdsp’s wdf library to generate a VST3 plug-in that can be loaded into digital audio worksta-tions. The plug-in has oversampling capabilities to preserve the adequate behavior of the circuit at frequencies close to Nyquist. The performance and accuracy of the Python model was measured, and the C++ im-plementation compared against another open-source implementation of the circuit using WDFs and R-Type adaptors (developed in the Faust programming language). The final EQP-1A Python model was 75% faster than our own one that used R-Type adaptors and the C++ implementation was 40% faster than the EQP-1A implemen-tation in Faust and a much more accurate emulation of the original circuit

Examining the Oscillator Waveform Animation Effect

An enhancing effect that can be applied to analogue oscillators in subtractive synthesizers is termed Animation, which is an efficient way to create a sound of many closely detuned oscillators playing in unison. This is often referred to as a supersaw oscillator. This paper first explains the operating principle of this effect using a combination of additive and frequency modulation synthesis. The Fourier series will be derived and results will be presented to demonstrate its accuracy. This will then provide new insights into how other more general waveform animation processors can be designed

An Exploratory Study of the Distortion Characteristics of Valve Signal Processors

Thesis (MMus)--Stellenbosch University, 2021ENGLISH ABSTRACT: Valve signal processors, a technology ostensibly out of place in the modern world, are still widely used in professional audio practice. It is believed that valves can impart a euphonic timbre on audio signals, in a phenomenon known colloquially as signal colouration. The inherent electronic limitations of valve signal processing result in a variety of distortions to be generated. Subsequently, the generation of distortion corresponds to the emergence of signal colouration. The standard distortion testing methodologies ordinarily employed by engineers have been limited as an analysis tool. These tests were originally designed to analyse the total amount of distortion present in a signal, not the intrinsic distortion character of a signal processor. Therefore, the objective of this thesis was to explore the key characteristics of valve signal processing distortion. The approach to empirical research adopted for this thesis involved the design and implementation of a series of exploratory experiments intended to analyse distortion character. Experiments were conducted on a selection of devices. Data was acquired from three software emulators, and a hardware valve microphone pre-amplifier. The microphone pre-amplifier was able to use two different types of valve for its gain stages, a 12AY7 and 12AX7; data was gathered from both. To make inferences into the processes that lead to the emergence of distortion, MATLAB was used to plot the electronic characteristics of a valve gain stage for analysis, thus permitting the juxtaposition of electronic phenomena to distortion measurements. The research was definitive in finding that different signal processors generate idiosyncratic profiles o f d istortion; t he e xtent t o which t his o ccurred s urpassed p rior a ssumptions. Each device produced distortion profiles that were not static, but dynamic, and evolved with varying input levels. These results suggest that different signal processors can cause distinct timbral changes to audio material under certain conditions.AFRIKAANSE OPSOMMING: Alhoewel vakuumbuise nie meer algemeen gebruik word in in moderne elektronika nie, word dit steeds wyd aangewend in klankverwerking waar die seinverkleuring wat deur die vakuumbuis se nie-liniere gedrag, gewensd is. Die verskeie tipes klankvervorming wat vakuumbuise skep veroorsaak kombineer tot ’n ontluikende effek in die vorm van klankverkleuring. Standaardtoesprosedures wat gebruik word om seinvervorming te meet is gerig daarop om die totale vervorming te meet en nie die spesifieke eienskappe van vervorming wat hoog aangeprys word vanuit ’n toonkleurperspektief nie. Die doelstelling van hierdie tesis was om die kerneienskappe van vakuumbuisvervorming op klankseine te verken. Die empiriese navorsing in hierdie tesis is die ontwerp en implementering van ’n reeks verkennende eksperimente om vakuumbuisvervorming te analiseer. Eksperimente is uitgevoer op ’n verskeidenheid van toestelle. Data is gemyn van drie sagteware-emulators en ’n vakuumbuis mikrofoonvoorversterker. Die mikrofoonvoorversterker was in staat om twee verskillende tipes vakuumbuise in die aanwinsvlak te gebruik, ’n 12AY7 en 12AX7 buis. Om afleidings te maak omtrent die prosesse wat lei tot die ontluiking van ververvorming, is MATLAB gebruik om die elektroniese eienskappe van ’n vakuumbuisbuisaanwinsvlak te stip vir ontledingsdoeleindes. Dit stel ’n vergelyking van elektroniese eienskappe met vervormingsmeting in staat. Die navorsing het bevind dat verskillende seinverwerkers unieke vervormingsprofiele genereer en die mate waartoe dit plaasvind het voormalige aannames oortref. Elke toestel het vervormseienskappe vertoon wat dinamies is en wat verander op grond van die intreeseinvlakke. Die resultate vertoon die invloed van verskillende seinverwerkers op toonkleureienskappe onder sekere toestande.Master

Advances in Solid State Circuit Technologies

This book brings together contributions from experts in the fields to describe the current status of important topics in solid-state circuit technologies. It consists of 20 chapters which are grouped under the following categories: general information, circuits and devices, materials, and characterization techniques. These chapters have been written by renowned experts in the respective fields making this book valuable to the integrated circuits and materials science communities. It is intended for a diverse readership including electrical engineers and material scientists in the industry and academic institutions. Readers will be able to familiarize themselves with the latest technologies in the various fields