Developing Virtual Synthesizers with VCV Rack

Leonardo Gabrielli

• Publisher: Focal Press
• Year: 2020
• Print ISBN:
  9780367077730
  9780367077747
• Edition: 1
• eBook ISBN:
  9780429663321
• Topic: Computer Science
• Subtopic: Computer Science General
• Index: Computer Science

Developing Virtual Synthesizers with VCV Rack takes the reader step by step through the process of developing synthesizer modules, beginning with the elementary and leading up to more engaging examples. Using the intuitive VCV Rack and its open-source C++ API, this book will guide even the most inexperienced reader to master efficient DSP coding to create oscillators, filters, and complex modules.

Examining practical topics related to releasing plugins and managing complex graphical user interaction, with an intuitive study of signal processing theory specifically tailored for sound synthesis and virtual analog, this book covers everything from theory to practice. With exercises and example patches in each chapter, the reader will build a library of synthesizer modules that they can modify and expand.

Supplemented by a companion website, this book is recommended reading for undergraduate and postgraduate students of audio engineering, music technology, computer science, electronics, and related courses; audio coding and do-it-yourself enthusiasts; and professionals looking for a quick guide to VCV Rack. VCV Rack is a free and open-source software available online.

CHAPTER 1

Modular Synthesis: Theory

The scope of this book is twofold: while focusing on modular synthesizers – a very fascinating and active topic – it tries to bootstrap the reader into the broader music-related DSP coding, without the complexity introduced by popular DAW plugin formats. As such, an introduction to modular synthesis cannot be neglected, since Rack is heavily based on the modular synthesis paradigm. More specifically, it faithfully emulates Eurorack mechanical and electric standards. Rack, as the name tells, opens up as an empty rack where the user can place modules. Modules are the basic building blocks that provide all sorts of functionalities. The power of the modular paradigm comes from the cooperation of small, simple units. Indeed, modules are interconnected at will by cables that transmit signals from one to another.

Although most common hardware modules are analog electronic devices, I encourage the reader to remove any preconception about analog and digital. These are just two domains where differential equations can be implemented to produce or affect sound. With Rack, you can add software modules to a hardware setup (Section 11.3 will tell you how), emulate complex analog systems (pointers to key articles and books will be provided in Section 11.1), or implement state-of-the-art numerical algorithms of any sort, such as discrete wavelet transform, non-negative matrix factorization, and whatnot (Section 11.2 will give you some ideas). To keep it simple, this book will mainly cover topics related to oscillators, filters, envelopes, and sequencers, including some easy virtual analog algorithms, and provide some hints to push your plugins further.

1.1 Why Modular Synthesis?

Why do we need modularity for sound generation?

Most classical and contemporary music is structured using modules, motives, and patterns. Most generating devices can be divided into modules either physically or conceptually. I know, you cannot split a violin in pieces and expect them to emit sound singularly. But you can still analytically divide the string, the bridge, and the resonant body, and generate sound by emulating their individual properties and the interconnection of the three.

Modularity is the direct consequence of analytical thinking. Describing the whole by dividing it into simpler components is a strategy adopted in most scientific and engineering areas. Unfortunately, studying the interconnection between the parts is often left “for future works.” Sometimes it does no harm, but sometimes it leaves out the largest part of the issue.

I like to think about the modular sound generation paradigm as the definitive playground to learn about the concept of separation and unity and about the complexity of nonlinear dynamical systems. Even though each module in its own right is well understood by its engineer or developer, the whole system often fails to be analytically tractable, especially when feedbacks are employed. This is where the fun starts for us humans (a little bit less fun if we are also in charge of analyzing it using mathematical tools).

1.2 An Historical Perspective

1.2.1 The Early Electronic and Electroacoustic Music Studios

As electronic music emerged in the twentieth century, a large part of the experimental process involved with it is related to the first available electronic devices, which were often built as rackmount panels or heavy cabinets of metal and wood. The 1950s are probably the turning point decade in the making of electronic music. Theoretical bases had been set in the first half of the century by composers and engineers. The invention of the positive feedback oscillator (using vacuum tubes) dates back to 1912–1914 (done independently by several researchers and engineers), while the mathematical formalization of a stability criterion for feedback systems was later devised by Heinrich Barkhausen in 1921. The field-effect transistor was patented in 1925 (in Canada, later patented in the US as patent no. 1,745,175), although yet unfeasible for its manufacturing complexity. After World War II, engineering had evolved wildly in several fields, following, alas, the war’s technological investment, with offspring such as control theory and cybernetics. Purely electronic musical instruments were already available far before the end of the war (e.g. the Theremin in 1920 and the Ondes Martenot in 1928), but still relegated to the role of classical musical instruments. Noise had been adopted as a key concept in music since 1913 with Luigi Russolo’s futurist manifest L’arte dei rumori, and atonality had been developed by composers such as Arnold Schoenberg and Anton Webern. In the aftermath of World War II, an evolution was ready to start.

A part of this evolution was driven by European electronic and electroacoustic music studios, most notably the WDR (Westdeutscher Rundfunk) in Cologne, the RTF (Radiodiffusion-Télévision Française) studio in Paris, and the Centro di Fonologia at the RAI (Radiotelevisione Italiana) studios in Milan.

The Cologne studio was born in the years 1951–1953. Werner Meyer-Eppler was among the founders, and he brought his expertise as a lecturer at the University of Bonn in electronic sound production (Elektrische Klangerzeugung) into the studio. Karleinz Stockhausen was involved from 1953, playing a key role in the development of the studio. He opposed to the use of keyboard instruments of the time (e.g. the Melochord¹ and the Monochord, introduced in the studio by Meyer-Eppler) and turned to a technician of the broadcast facility, Fritz Enkel, for getting simple electronic devices such as sine wave generators.

The Paris studio was employed by the Groupe de Recherches Musicales, which featured pioneers Pierre Schaeffer, Pierre Henry, and Jacques Poullin, and was mostly based on Schaeffer’s concepts of concrete music, and therefore mostly oriented to tape works and electroacoustic works.

Finally, the studio in Milan was born officially in 1955 and run by composers Luciano Berio and Bruno Maderna and technician Marino Zuccheri. Most of the equipment was designed and assembled by Dr. Alfredo Lietti (1919–1998), depicted in Figure 1.1 in front of his creatures. It is interesting to note that Lietti started his career as a radio communication technician, showing again how communication technology had an impact on the development of electronic music devices. The Studio di Fonologia at its best boasted third-octave and octave filter banks, other bandpass filters, noise and tone generators, ring modulators, amplitude modulators, a frequency shifter, an echo chamber, a plate reverb, a mix desk, tape recorders, various other devices, and the famous nine sine oscillators (Novati and Dack, 2012). The nine oscillators are often mentioned as an example of how so few and simple devices were at the heart of a revolutionary musical practice (Donati and Paccetti, 2002), with the stigmatic statement “Avevamo nove oscillatori,” we only had nine oscillators.

Figure 1.1: C.1960, Alfredo Lietti at the Studio di Fonologia Musicale, RAI, Milan. Lietti is shown standing in front of rackmount devices he developed for the studio, mostly in the years 1955–1956. A cord patch bay is clearly visible on the right. Credits: Archivio NoMus, Fondo Lietti.

All the electronic music centers of the 1950s had rackmount oscillators, filter banks, modulators, and tape devices. These would be poor means by today’s standards to shape and arrange sound, yet they were exactly what composers required at the time to rethink musical creation. Reorganizing musical knowledge required elementary tools that would allow the composers to treat duration, dynamics, pitch, and timbre in analytical terms. The electronic devices used in these early electronic music studios were typically adapted from communication technology.² After all, these first studios were hosted by broadcast companies.

What was extraordinary about the first electronic and electroacoustic works of the 1950s was their eclecticism. It turned out that a few rudimentary devices were very flexible and could serve the grand ideas of experimental composers. The research directions that were suggested by early electronic and electroacoustic music composers of the time, such as Olivier Messiaen, Pierre Schaeffer, and Karleinz Stockhausen, proved fruitful. In the works of these studios, we can see the premises of the advent of modular synthesis, where electronic tools are employed creatively, suggesting an idea of the studio as a musical instrument or device. A few fundamental steps were still missing at the time:

• Packing a studio in a case (or in a laptop, as we do nowadays) was impossible. In the 1950s, the technology was yet underdeveloped in terms of integration, size, and power consumption. The first bipolar junction transistor had just been patented and produced in 1948 and 1950, respectively, at the Bell Labs, USA, and years of engineering were required to make production feasible on a large scale and with small form factors.
• Electronic music was very academic and far from audiences, except from early science fiction movies. These new forms of music would still take a couple of decades to leak into popular music, as we shall see in the next section.

1.2.2 The Birth and Evolution of Modular Synthesizers

In the US, things were moving fast from the technical side. In 1951, entertainment devices manufacturer RCA started a research project that led to the development of the RCA Sound Synthesizers Mark I and Mark II, hosted at Columbia University’s Computer Music Center. These were modular systems that could be patched by wires and follow a score programmed through punched paper, finally leading to a recording on a lacquer disc (or later to a magnetic tape). They were totally based on vacuum tubes and took up the space of an office. Serial music composers were interested in their capabilities and music programming flexibility, but they never had an impact in contemporary music, with Princeton University’s composer Milton Babbit being one of the few prominent users.

In those years, computer music centers were rising in the US. The first and major innovator in the field was Max Mathews. After taking its degree at the Massachusetts Institute of Technology in 1954, Max Mathews started working at Bell Labs in the US, where he devised – in a few years – most of the key concepts of computer music and digital sound synthesis through the development of MUSIC I and later versions. He is still regarded as one of the main innovators in the field. The concepts discussed in Section 4.1 were mostly there in Mathews’ works by the end of the 1950s.

The US, however, was also appealing to skilled inventors who sought commercial success and modern manufacturing facilities. German engineer Harald Bode, the creator of the aforementioned Melochord, moved to the US in 1954 to continue developing his ideas. He was among the first ones to foresee transistor technology as a key changer in designing synthesizers and the first to build a compact modular synthesizer. In his 1984 retrospective survey on musical effects, he states that “in the Melochord for the Stockhausen Studio in Cologne, the modular concept was adopted, by which external ring modulators, echo chambers, and the like could be included in the system” (Bode, 1984, p. 732). He also built a modular sound modification system between 1959 and 1960 (Bode, 1961), which included:

the multiplier-type ring modulator and other sound modifying devices […] such as an envelope follower, a tone-burst-responsive envelope generator, a voltage-controlled amplifier, formant and other filters, mixers, a pitch extractor, a comparator and frequency divider for the extracted pitch, and a tape loop repeater with dual channel processing. The modular concept proved attractive due to its versatility, and it was adopted by Robert Moog when he created his modular synthesizer in 1964.

(p. 733)

Robert Moog (1934–2005), who probably requires no introduction to any readers, started devel...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Preface
• Acknowledgments
• Chapter 1. Modular Synthesis: Theory
• Chapter 2. Elements of Signal Processing for Synthesis
• Chapter 3. VCV Rack Basics
• Chapter 4. Developing with VCV Rack
• Chapter 5. The Graphical User Interface: A Quick Introduction
• Chapter 6. Let’s Start Programming: The Easy Ones
• Chapter 7. Getting Serious DSP: “Classroom” Modules
• Chapter 8. Crunching Numbers: Advanced DSP Modules
• Chapter 9. The Graphical User Interface: Creating Custom Widgets
• Chapter 10. Additional Topics
• Chapter 11. After Reading This Book
• Bibliography
• Index