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

Newton-Raphson Solution of Nonlinear Delay-Free Loop Filter Networks

For their numerical properties and speed of convergence, Newton-Raphson methods are frequently used to compute nonlinear audio electronic circuit models in the digital domain. These methods are traditionally employed regardless of preliminary considerations about their applicability, primarily because of a lack of flexible mathematical tools making the convergence analysis an easy task. We define the basin delimiter, a tool that can be applied to the case when the nonlinear circuit is modeled by a delay-free loop network. This tool is derived from a known convergence theorem providing a sufficient condition for quadratic speed of convergence of the method. After substituting the nonlinear characteristics with equivalent linear filters that compute Newton-Raphson on the existing network, through the basin delimiter, we figure out constraints guaranteeing quadratic convergence speed in the diode clipper. Further application to a ring modulator circuit does not lead to comparably useful constraints for quadratic convergence; however, also in this circuit, the basin delimiter has a magnitude roughly proportional to the number of iterations needed by the solver to find a solution. Together, such case studies foster refinement and generalization of this tool as a speed predictor, with potential application to the design of virtual analogue systems for real-time digital audio effects

Deep Learning for Black-Box Modeling of Audio Effects

Virtual analog modeling of audio effects consists of emulating the sound of an audio processor reference device. This digital simulation is normally done by designing mathematical models of these systems. It is often difficult because it seeks to accurately model all components within the effect unit, which usually contains various nonlinearities and time-varying components. Most existing methods for audio effects modeling are either simplified or optimized to a very specific circuit or type of audio effect and cannot be efficiently translated to other types of audio effects. Recently, deep neural networks have been explored as black-box modeling strategies to solve this task, i.e., by using only input–output measurements. We analyse different state-of-the-art deep learning models based on convolutional and recurrent neural networks, feedforward WaveNet architectures and we also introduce a new model based on the combination of the aforementioned models. Through objective perceptual-based metrics and subjective listening tests we explore the performance of these models when modeling various analog audio effects. Thus, we show virtual analog models of nonlinear effects, such as a tube preamplifier; nonlinear effects with memory, such as a transistor-based limiter and nonlinear time-varying effects, such as the rotating horn and rotating woofer of a Leslie speaker cabinet

Uso de processamento digital de áudio na implementação de efeitos em instrumentos musicais

Monografia (graduação)—Universidade de Brasília, Instituto de Ciências Exatas, Departamento de Ciência da Computação, 2015.Este trabalho tem por objetivo apresentar ao leitor alguns dos principais efeitos de áudio presentes no mercado musical. Além de informações relacionadas ao surgimento e evolução do mundo dos efeitos de áudio, como os primeiros efeitos, a transição do domínio analógico para o domínio digital, será abordada a teoria por trás do processamento do sinal dentro de cada efeito, bem como a estruturação e uma implementação na linguagem Csound de cada um dos efeitos apresentados. Por fim, interliga-se todas as implementações de efeitos de forma a criar-se um sistema de processamento multi-efeitos em CSound.This work has the objective of presenting to the reader some of the main audio processing effects in the musical industry. Along with the information about the creation and the evolution of the audio effects, like the first e effects, the transition from analog to digital, the theory behind the signal processing within each effect will be explained, as well as the implementation of each presented effect in the Csound programming language. Lastly, all the effect implementation are linked to create a Csound multi-effects processing system

Implementação digital da caixa Leslie em espaço livre

O presente trabalho aborda os fundamentos teóricos da descrição e discretização dos efeitos gerados pela caixa Leslie, a fim de se produzir um sistema embarcado capaz de simula-lá. Os efeitos trazidos pela Leslie são: a distorção harmônica, a separação entre as frequências graves e agudas entorno dos 800Hz, o efeito Doppler e a modulação em amplitude. Tais efeitos foram quantificados e discretizados em forma de algoritmos. Esses algoritmos foram simulados no MATLAB 2012b e transcritos para linguagem C++, a fim de se programar o sistema dentro da placa de desenvolvimento Teensy 3.6. Projetou-se circuitos periféricos para adequação dos sinais de entrada e saída, e desenvolveu-se um circuito capaz de fornecer tensão simétrica nos níveis de -5V, 0V e 5V para alimentar o pedal. A sonoridade resultante foi comparada a do pedal RT-20 da BOSS em diferentes configurações com senoides e ondas triangulares de entrada. Apesar das sonoridades resultantes se aparentarem, o formato dos sinais de saída para frequências acima da frequência de 800Hz se mostraram bastante distintos, enquanto que sinais abaixo dessa frequência tiveram maior semelhança. As discrepâncias foram atribuídas ao fato do sistema implementar aproximações dos efeitos Doppler e da modulação em amplitude, e não implementar as múltiplas reflexões do som que ocorrem dentro da caixa. Entretanto, agregada às múltiplas combinações de variações dos parâmetros dos efeitos, tal pedal seria capaz de simular aspectos não considerados de outros modelos e outros efeitos que se baseiam nos da Leslie.This paper intends to approach the theoretical foundations of the description and discretization of Leslie cabinet’s effects, in order to produce an embedded system capable of simulate it. The Leslie’s effects over an input sound are: the harmonic distortion, the crossover between the treble and the bass sounds over 800Hz, the Doppler effect and the amplitude modulation. The effects were quantified and discretized into algorithms. These algorithms were simulated in MATLAB 2012b and converted to C++ in the Teensy 3.6 development board. An input and output circuits were designed to suit the signals, and a symmetric supply circuit were also designed to provide -5V, 0V and 5V voltage levels. The resulting sounds of the pedal were compared to the BOSS’ RT-20 pedal in different configurations with sine and triangular waves input signals. Although the resulting sonority was similar, the shape of the output signals to frequencies above 800Hz were very distinct, while the signals under this frequency had more similarities. Those nonconformities were attributed to the approximations in the Doppler effect and the amplitude modulation, joined to the multiple feedback non-inplementation of the sound in the Leslie’s interior. However, joined to the multiple combinations of the parameters’ variations, the pedal would be capable of simulate non-considered aspects of other models and effects based on the Leslie

An Investigation into Non-linear Distortion Pedals with a Focus on Establishing a Lexicon to Accurately Describe Them.

This thesis attempts to identify and investigate the auditory impact distortion pedals impart on the source signal and consequently, how best to define, discuss and classify their individual, and collective, sonic signatures. This includes establishing a specialist lexicon with recontextualised descriptions for the specific adjectives of focus through means of both qualitative and quantative experimentation. This information is then visually represented by a ‘distortion wheel’ based in principle off the SCAA’s Coffee Tasting Wheel and how that allowed for the accessible retrieval of specialist terms within the contextual field. This is achieved through a series of etymological and audio-based analysis and experimentation. Qualitative experimentation was used to discover the initial descriptor list, critical sonic variables, and to subsequently define the words; quantative to match respective audio and signal analysis to the linked adjectives. The results showed ‘crunchy’ to be the most commonly used distortion descriptor. Through further analysis, it can be concluded that the Ibanez TS-9 is the crunchiest distortion pedal as its sonic features match closest to the defining traits of ‘crunchy’. Distortion pedals are subsequently successfully classified and descriptions for each adjective created to give the completed distortion lexicon