2036 lines
43 KiB
Text
2036 lines
43 KiB
Text
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noindent
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SAE Berlin
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Student Id: 18128
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Course: AED412
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\begin_layout Plain Layout
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Headinstructor: Boris Kummerer
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Berlin, Germany 2012
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author{
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by Karl Pannek
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}
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title{
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LARGE{Prototyping a Modular Analog Synthesizer}}
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Table of Contents
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\begin_layout Chapter
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Introduction
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\begin_layout Section*
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Motivation
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The project was inspired by the film
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\emph on
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moog
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citealp{Fjellestad:movie}}
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, a documentary about Dr.
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Robert Moog, electronic instrument pioneer and inventor.
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Its goal is to convey an understanding of the inner workings of electronic
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synthesizers and their components.
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||
The reader is guided through the process of creating a small but functional
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modular synthesizer setup that is fun to play and experiment with.
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||
The intention was to investigate the possibilities and limits in designing
|
||
and building an analog sound device for someone, who had not been in contact
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with analog synthesizers, let alone building electronics devices before.
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\begin_layout Section*
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Chapter Overview
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The first chapter represents the research on the historical background of
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analog synthesizers since the beginning of the twentieth century.
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It was tried to outline important milestones in the historic development
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from the first electronic sound generating devices until a point in time
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when manufacturers of modular synthesizers have developed a profitable
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market.
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\begin_layout Standard
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Subsequently the most important concepts of subtractive synthesis are summarized.
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A general overview over common sound generation and processing methods
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is given, whereby all concepts are applicable to both analog and digital
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synthesis.
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In chapter three these concepts are taken one step further and discussed
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in the context of electronic circuitry.
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Lastly the process of building an electronic synthesizer prototype is described.
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status collapsed
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The process of building the prototype includes working with an oscilloscope
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to examine and verify the shape of various waveforms before and after modulatio
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n.
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To make it playable with a keyboard, a MIDI input module is added.
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It features an Arduino microprocessor to convert digital MIDI messages
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into control voltage outputs that other modules can connect to.
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It is the only digital component of the synthesizer, while tone generation
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and processing are analog.
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\begin_layout Section*
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||
A Personal Journey
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||
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As a trained programmer and web application developer the field of electronic
|
||
engineering always seemed appealing to me.
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Hence the assignment for a research paper during the audio engineering
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course at SAE Institute seemed like a welcome opportunity to dive into
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the realm of building electronic devices in the context of sound generation
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and modification.
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\end_layout
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\begin_layout Standard
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The process of writing this paper has been an unexpectedly rewarding and
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inspiring experience, pushing the boundaries of my own musical and technical
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understanding.
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||
Most notably the concepts of free composition - meaning allowing randomness
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||
and therefore putting oneself in the position of reacting to a musical
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||
system, influencing it in terms of tendencies, rather than controlling
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||
it with a predetermed mindset - has been something that really changed
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my perseption of musical creativity.
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||
This for me seems much more attainable in the analog world, where electrical
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||
components and signal chains can be brought to their tipping points, resulting
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in an unpredictable outcome.
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||
That is where sound exploration begins, which is a totally different experience
|
||
than knowing what will happen.
|
||
Virtual digital environments, which I was familiar with on the other hand,
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||
generally seem to tend persuade the user to feel in control at all times.
|
||
\end_layout
|
||
|
||
\begin_layout Chapter
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Historic Evolution of the Synthesizer
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||
\end_layout
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||
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\begin_layout Section
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Early Development Milestones
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status collapsed
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Electric instruments at that time were developed primarily to imitate and
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evolve the sounds of classical instruments and therefore satisfy traditional
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ideas of musical writing
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citealp[p.~12]{Manning1985}}
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||
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\end_layout
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\end_inset
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|
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|
||
|
||
\begin_layout Standard
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Around 1900 american Thadedeus Cahill initiated a new era of music by inventing
|
||
a 200 ton machine known as the Dynamophone or Thelharmonium
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citealp[p.~19]{Humpert1987}}
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.
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It was an electrical sound generator, that produced alternating sine wave
|
||
shaped currents of different audio frequencies.
|
||
A modified electrical dynamo was used in conjunction with several specially
|
||
geared shafts and inductors to create the signals.
|
||
The Dynamophone could be played with a polyphonic keyboard and featured
|
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special acoustic horns to convert the electrical vibrations into sound
|
||
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|
||
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.
|
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The timbre of the instrument was shaped from fundamentals and overtones.
|
||
This is known as the principle of additive synthesis
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|
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citealp[p.~730]{Bode1984}}
|
||
\end_layout
|
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|
||
\end_inset
|
||
|
||
.
|
||
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|
||
|
||
\begin_layout Standard
|
||
In 1924 the russian inventor Leon Theremin created the Aetherophone, which
|
||
would later be known as the Theremin.
|
||
Unlike most electric instrument developed around that time, the Theremin
|
||
had no keyboard.
|
||
It was played merely by hand motion around two capacitive detecors, that
|
||
generated electrical fields.
|
||
These were affected by the electric capacity of the human body.
|
||
One of these detectors was a vertical rod to control dynamics and the other
|
||
a horizontal loop to change the pitch
|
||
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|
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|
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|
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|
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|
||
.
|
||
|
||
\begin_inset Quotes eld
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||
\end_inset
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||
|
||
The theatricality of its playing technique and the uniqueness of its sound
|
||
made the Theremin the most radical musical instrument innovation of the
|
||
early 20th century.
|
||
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|
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|
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|
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|
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|
||
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|
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|
||
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|
||
Some organ-like precursors to the synthesizer were the Ondes Martenot and
|
||
the Trautonium, which were devised just a few years later.
|
||
The Ondes Martenot is one of the few early electric instruments, that are
|
||
still in concert- and theatre use in their original design today
|
||
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|
||
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|
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.
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
The Givelet (1929) was a commercially more successful instrument, since
|
||
it was designed as a cheap alternative to pipe organs.
|
||
These instruments were polyphonic and unified the concepts of the Pianola
|
||
- a self-playing piano, controlled by pre-punched tape - with electronic
|
||
sound genaration.
|
||
The ability to program electronic sounds should lead the way for future
|
||
devices such as the RCA synthesizer or computer music production in general.
|
||
However, the Givelet was about to take a back seat, when Laurens Hammond
|
||
published his Hammond Organ in 1935.
|
||
Its technical operation principle is reminiscent of the Dynamophone, since
|
||
it also involved rotating discs in a magnetic field
|
||
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\end_inset
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|
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.
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
The german engineer Harald Bode contributed to the design of several new
|
||
instruments from the 1930's on, like the warbo formant organ (1937) or
|
||
later the Melochord (1949).
|
||
He was primarily interested in providing tools for a wide range of musicians,
|
||
which is why his contributions straddled between the two major design tradition
|
||
s of new sounds versus imitation of traditional ones.
|
||
He turned out to be one of central figures in the history of electronic
|
||
music, since he was also one of the primary engineers in establishing the
|
||
classic tape music studio in europe
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
citetext{
|
||
\backslash
|
||
citealp[p.~9]{Dunn1992}}
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
.
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
Bode was one of the first engineers to grasp the significance of the invention
|
||
of the solid state transistor for sound synthesis.
|
||
In an article published in 1961 he draws particular attention to the advanteges
|
||
of modular design.
|
||
|
||
\begin_inset Quotes eld
|
||
\end_inset
|
||
|
||
The versatility of transistor-based electronics made it possible to design
|
||
any number of devices which could be controlled by a common set of voltage
|
||
characteristics.
|
||
\begin_inset Quotes erd
|
||
\end_inset
|
||
|
||
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
citetext{
|
||
\backslash
|
||
citealp[p.~117]{Manning1985}}
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
.
|
||
But it was not until the early 1960's that major advances in electronic
|
||
design took shape
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
citetext{
|
||
\backslash
|
||
citealp[p.~19]{Dunn1992}}
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
.
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
\begin_inset Note Note
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
Sakbutt (1948) Hugh LeCaine
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Section
|
||
The First Synthesizers
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
In 1955 the laboratories of the Radio Corporation of America (RCA) introduced
|
||
a new and very advanced machine to the public named the Olson-Belar Sound
|
||
Synthesizer, later known as the RCA Mark I Music Synthesizer.
|
||
It combined many means of tone generation and sound modification known
|
||
at the time and is considered the first synthesizer.
|
||
Mark I was built with the specific intention of imitating traditional instrumen
|
||
t sounds and to reduce the costs of the production of popular music by replacing
|
||
musicians.
|
||
However, the machine proved unsuitable for its original intent and was
|
||
later used completely for electronic music experimentation and composition
|
||
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
citetext{
|
||
\backslash
|
||
citealp[p.~15-16]{Dunn1992}}
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
.
|
||
The synthesizer could not be played in the conventional sense in real time.
|
||
Instead musical information had to be pre programmed as punched holes in
|
||
a large paper tape.
|
||
Harry Olson and Herbert Belar produced an improved Mark II Synthesizer
|
||
in 1957, which the nickname
|
||
\emph on
|
||
Victor
|
||
\emph default
|
||
was given
|
||
\emph on
|
||
|
||
\emph default
|
||
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
citetext{
|
||
\backslash
|
||
citealp{Bear:website}}
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
.
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
Around the same time the outstanding guitarist and inventor Les Paul became
|
||
famous with his multitrack guitar recordings.
|
||
He stimulated many innovators not only with the success of his multitrack
|
||
recorder, but also with his methods of electronic sound processing.
|
||
Harald Bode was so impressed and inspired by his work, that he built a
|
||
system consisting of a number of electronic modules for sound modification
|
||
in late 1959 through 1960.
|
||
His system featured ring modulator devices, envelope followers and generators,
|
||
voltage-controlled amplifiers, filters, mixers and others
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
citetext{
|
||
\backslash
|
||
citealp[p.~733]{Bode1984}}
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
.
|
||
The modular concept of his device had proven attractive due to its versatility
|
||
and predicted the more powerful modular synthesizers that emerged in the
|
||
early 1960's
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
citetext{
|
||
\backslash
|
||
citealp[p.~20]{Dunn1992}}
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
.
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
In 1963 Robert Moog, a passionate inventor from Ithaca, New York, was selling
|
||
kits of transistorized Theremins
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
citetext{
|
||
\backslash
|
||
citealp[p.~20]{Dunn1992}}
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
.
|
||
As he states in the movie about him
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
citetext{
|
||
\backslash
|
||
citealp{Fjellestad:movie}}
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
, he had been completely obsessed with building and later designing Theremins
|
||
since the age of 14.
|
||
A year later he built a transistor based voltage-controlled oscillator
|
||
and amplifier for the composer Herbert Deutsch.
|
||
This led moog to the presentation of a paper entitled
|
||
\emph on
|
||
Voltage-Controlled Electronic Music Modules
|
||
\emph default
|
||
at the sixteenth annual convention of the Audio Engineering Society, which
|
||
had stimulated widespread interest
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
citetext{
|
||
\backslash
|
||
citealp[p.~117-118]{Manning1985}}
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
.
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
Similar developments had been taking place at the west coast of the united
|
||
states.
|
||
Morton Subotnick and Ramon Sender started their carreer in electronic music
|
||
experimentation, and became increasingly dissatisfied with the severe limitatio
|
||
ns of traditional equipment at the San Francisco Tape Music Center, where
|
||
they were working.
|
||
They sought out to hire a competent engineer and met Donald Buchla
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
citetext{
|
||
\backslash
|
||
citealp[p.~117-118]{Manning1985},
|
||
\backslash
|
||
citealp[p.~22]{Dunn1992}}
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
.
|
||
Their discussions resulted in the concept of a modular voltage-controlled
|
||
system.
|
||
Buchla's design approach differed significantly from Moog.
|
||
He rejected the idea of a synthesizing familiar sounds and resisted the
|
||
word
|
||
\emph on
|
||
synthesizer
|
||
\emph default
|
||
ever since.
|
||
It seemed much more interesting to emphasize new timbral possibilities
|
||
and stress the complexity that could arise from randomness.
|
||
At the same time Buchla was fascinated with designing control devices other
|
||
than the standard keyboard, which Moog decided to use for playing
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
citetext{
|
||
\backslash
|
||
citealp[p.~20]{Dunn1992}}
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
.
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
In 1966 Bob Moogs first production model was available from the business
|
||
R.A.
|
||
Moog Co.
|
||
that he had founded
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
citetext{
|
||
\backslash
|
||
citealp[p.~20]{Dunn1992}}
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
.
|
||
At this time Walter Carlos, an audio engineer from New York who adviced
|
||
Bob Moog while perfecting his system, worked with Benjamin Folkman to produce
|
||
an album of titles by Johann Sebastian Bach interpreted only with Moog
|
||
synthesizers.
|
||
With the title
|
||
\emph on
|
||
Switched-on Bach
|
||
\emph default
|
||
they demonstrated the performance of the system so convincingly, that they
|
||
hit the popmusic charts and sold a million LP's
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
citetext{
|
||
\backslash
|
||
citealp[p.~45]{Ruschkowski1990}}
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
.
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
By the end of the decade two other manufactrurers entered the market: ARP
|
||
in America and EMS Ltd.
|
||
in England.
|
||
They had become major rivals for Moog and Buchla.
|
||
Synthesizer production was dominated by these four companies for several
|
||
years, whereby each firm struggled for a major share of a highly lucrative,
|
||
rapidly expanding market
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
citetext{
|
||
\backslash
|
||
citealp[p.~118]{Manning1985}}
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
.
|
||
\end_layout
|
||
|
||
\begin_layout Chapter
|
||
Theory of Subtractive Synthesis
|
||
\end_layout
|
||
|
||
\begin_layout Section
|
||
Sources
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
Acoustic events can generally be divided in two groups: noises and tones.
|
||
Whereas tones - as opposed to noise - are classified as sound waves, that
|
||
oscillate in a periodic manner.
|
||
However this is only a theoretical classification, since most natural sounds
|
||
are a combination of the two
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
citetext{
|
||
\backslash
|
||
citealp[p.~52]{Ruschkowski1990}}
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
.
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Subsection
|
||
Wave Oscillation
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
At the root of every artificial tone generating system there is an element
|
||
that produces an oscillation.
|
||
This element is mostly described as the oscillator, which represents the
|
||
very source of what can be heard eventually.
|
||
The oscillator produces a periodic wave, that moves between an amplitude-minima
|
||
and -maxima.
|
||
Its waveform (shape of the wave) determines the overtone structure and
|
||
therefore the timbre of this basic source sound.
|
||
Oscillators often provide several waveforms between which it is possible
|
||
to switch back and forth.
|
||
The pitch of the output signal is defined by the frequency of the wave
|
||
and must oscillate between 20Hz and 20kHz in order for it to be audible
|
||
to humans
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
citetext{
|
||
\backslash
|
||
citealp[p.~124]{Friesecke2007}}
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
.
|
||
The output signal can later be processed and modulated in several ways.
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
Oscillators that swing at an infrasonic frequency - meaning a frequency
|
||
so low, that it is not hearable anymore - are called low frequency oscillators
|
||
(LFO).
|
||
They are used to control parameters of different components of the synthesizer
|
||
periodically.
|
||
For example to influence the pitch of another oscillator to get a vibrato
|
||
- or the amplitude to get a tremolo effect.
|
||
Some oscillators frequencies range from very low to very high, in which
|
||
case a distinction between oscillator and LFO is unnecessary.
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
\begin_inset Note Note
|
||
status collapsed
|
||
|
||
\begin_layout Plain Layout
|
||
Difference between poly and monophonic synthesis (voices, mono: store last
|
||
note value) Voices
|
||
\end_layout
|
||
|
||
\begin_layout Plain Layout
|
||
unison
|
||
\end_layout
|
||
|
||
\begin_layout Plain Layout
|
||
sync
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Subsubsection
|
||
Characteristics of Common Waveforms
|
||
\end_layout
|
||
|
||
\begin_layout Labeling
|
||
\labelwidthstring 00.00.0000
|
||
sine The most basic waveform is the sine wave.
|
||
It contains no overtones at all and sounds round and dull.
|
||
\end_layout
|
||
|
||
\begin_layout Labeling
|
||
\labelwidthstring 00.00.0000
|
||
sawtooth The sawtooth, also known as saw or ramp waveform sounds very bright,
|
||
sometimes described as trompet-like
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
citetext{
|
||
\backslash
|
||
citealp[p.~49]{Anwander2011}}
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
.
|
||
It consist of a complete series of harmonics and is therefore well suited
|
||
for subtractive synthesis.
|
||
There are two types of sawtooth waves: rising and descending.
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Labeling
|
||
\labelwidthstring 00.00.0000
|
||
triangle Composed of only odd harmonics, the triangle wave has a much softer,
|
||
flute-like sound.
|
||
\end_layout
|
||
|
||
\begin_layout Labeling
|
||
\labelwidthstring 00.00.0000
|
||
square Also known as rectangle,
|
||
\begin_inset Note Note
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
clearify difference to triangle
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
the square wave also consists of odd harmonics only.
|
||
Its timbre reminds of woodwind instruments
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
citetext{
|
||
\backslash
|
||
citealp[p.~55]{Ruschkowski1990}}
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
.
|
||
A true square wave has a 50 % duty cycle - equal high and low periods.
|
||
However, oscillators often feature a pulse width parameter, trough which
|
||
the high-low time ratio can be accessed.
|
||
This has a distinct influence on the wave's timbre.
|
||
In this case, the square becomes a pulse waveform.
|
||
\end_layout
|
||
|
||
\begin_layout Subsection
|
||
Noise Generation
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
A different approach on the creation of source audio material is resembled
|
||
by noise generators, which generate random non-periodic frequencies.
|
||
Therefore the signal contains no tonal information.
|
||
\end_layout
|
||
|
||
\begin_layout Subsubsection
|
||
Noise Types
|
||
\end_layout
|
||
|
||
\begin_layout Labeling
|
||
\labelwidthstring 00.00.0000
|
||
white Equal power density in any band of the frequency spectrum
|
||
\end_layout
|
||
|
||
\begin_layout Labeling
|
||
\labelwidthstring 00.00.0000
|
||
pink Power density decreases by 3dB per octave; also referred to as 1/f
|
||
noise
|
||
\end_layout
|
||
|
||
\begin_layout Labeling
|
||
\labelwidthstring 00.00.0000
|
||
brown Power density decreases by 6dB per octave; also referred to as 1/f
|
||
\begin_inset script superscript
|
||
|
||
\begin_layout Plain Layout
|
||
2
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
noise
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
The names of these noise types were derived from the spectral distribution
|
||
of the correspondingly colored light
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
citetext{
|
||
\backslash
|
||
citealp[p.~155]{Friesecke2007}}
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
.
|
||
\end_layout
|
||
|
||
\begin_layout Subsection
|
||
Triggering Notes
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
In order to use the previously discussed signal generators in a musical
|
||
context, it is necessary to cut off their stationary signals when no note
|
||
is being played.
|
||
This is accomplished by routing the output signal of the generator to an
|
||
amplifier and providing it with a gate signal.
|
||
The source of the gate signal can be a keyboard or a sequencer, which would
|
||
also send a pitch value to the oscillator to set its frequency
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
citetext{
|
||
\backslash
|
||
citealp[p.~36]{Anwander2011}}
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
.
|
||
\end_layout
|
||
|
||
\begin_layout Section
|
||
Signal Processing
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
In their raw shape the mentioned source signals sound rather underwhelming,
|
||
since they produce fixed timbres lacking of distinctive qualities
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
citetext{
|
||
\backslash
|
||
citealp[p.~49]{Manning1985}}
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
.
|
||
To get a more interesting sound, the signal can be manipulated in acoustic
|
||
colour or dynamics by one or more processing units.
|
||
\end_layout
|
||
|
||
\begin_layout Subsection
|
||
Dynamic Envelopes
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
The most important component responsible for shaping the dynamic structure
|
||
of a note is the envelope.
|
||
It is triggered by the the gate on/off signal and outputs a control signal
|
||
that fades between the different state phases of a note.
|
||
The rapidity of these changes is adjusted by parameters, that represent
|
||
these states.
|
||
Its output signal can be used to control an amplifier and therefore shape
|
||
the dynamic structure of the note.
|
||
The most common envelope type is the ADSR, which stands for attack, decay,
|
||
sustain, release.
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Labeling
|
||
\labelwidthstring 00.00.0000
|
||
Attack sets how long the envelope signal rises after a note was triggered
|
||
\end_layout
|
||
|
||
\begin_layout Labeling
|
||
\labelwidthstring 00.00.0000
|
||
Decay sets how long it takes for the envelope signal to drop from its maximum
|
||
to the sustain level after the attack phase was completed
|
||
\end_layout
|
||
|
||
\begin_layout Labeling
|
||
\labelwidthstring 00.00.0000
|
||
Sustain sets the output level for the time period after the decay phase
|
||
and before the gate signal was terminated
|
||
\end_layout
|
||
|
||
\begin_layout Labeling
|
||
\labelwidthstring 00.00.0000
|
||
Release sets the length of the fade out after the note has endede
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
Envelopes can also be used to control other parameters, for example the
|
||
cutoff frequency of a filter (see chapter
|
||
\begin_inset CommandInset ref
|
||
LatexCommand ref
|
||
reference "sub:filters"
|
||
|
||
\end_inset
|
||
|
||
).
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Subsection
|
||
Filtering
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
\begin_inset CommandInset label
|
||
LatexCommand label
|
||
name "sub:filters"
|
||
|
||
\end_inset
|
||
|
||
The filter is the processing component responsible for the sound changes,
|
||
that people associate with
|
||
\emph on
|
||
the typical synthesizer sound
|
||
\emph default
|
||
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
citetext{
|
||
\backslash
|
||
citealp[p.~53]{Anwander2011}}
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
.
|
||
They remove a spectrum of frequencies from their input signal above or
|
||
below the cutoff frequency and are often used in conjunction with an envelope
|
||
or LFO modulation on the cutoff.
|
||
This cutoff frequency is an important parameter determining the frequency
|
||
at which the signal begins to be attenuated.
|
||
The slew rate sets the slope of the filter - meaning how abrubt frequencies
|
||
are being cut.
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
Filters can generally be devided into two categories: Low pass and high
|
||
pass filters (also called high cut and low cut).
|
||
To get a bandpass filter, low- and high pass are connected in series.
|
||
When connected parallely, they become a bandstop or bandreject filter.
|
||
Lastly the allpass filter should be mentioned, which does not change the
|
||
frequency spectrum but merely influences the phase of the signal around
|
||
its cutoff
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
citetext{
|
||
\backslash
|
||
citealp[p.~55]{Anwander2011}}
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
.
|
||
|
||
\begin_inset Note Note
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
COVER RESONANCE!!!
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Section
|
||
Controllers
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
Controllers can be characterized by the way of how humans interact with
|
||
them and how their output signal is applied in controlling other components
|
||
of the system
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
citetext{
|
||
\backslash
|
||
citealp[p.~9]{Hutchins1975}}
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
.
|
||
A keyboard for example is a manual controller, since it is the movement
|
||
of the players fingers which are translated into a voltage or control value
|
||
and then used to control pitch and amplitude of a note.
|
||
The same applies for rotary knobs and faders or touch sensitive surfaces.
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
Sequencers on the other hand are programmable controllers.
|
||
They are not dependend upon a manual interaction except for their programming
|
||
and activation.
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Section
|
||
The Modular Approach
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
A modular synthesizer is an electronic instrument, where sound generators,
|
||
processors and control facilities are presented in separate independent
|
||
entities called modules.
|
||
These modules are not wired in a preconceived way, but connected together
|
||
with patchchords.
|
||
The second essential aspect is the concept of intermodular controllability,
|
||
with which modules may modulate or regulate the behaviour of other modules.
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Chapter
|
||
Analog Synthesis
|
||
\end_layout
|
||
|
||
\begin_layout Section
|
||
General
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
Voltage
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
Control Voltage Audio Signal
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
Current
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
Rotary Knob
|
||
\end_layout
|
||
|
||
\begin_layout Section
|
||
Modules
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
intermodular stuff like buffering
|
||
\end_layout
|
||
|
||
\begin_layout Subsection
|
||
Oscillator
|
||
\end_layout
|
||
|
||
\begin_layout Subsection
|
||
Filter
|
||
\end_layout
|
||
|
||
\begin_layout Subsection
|
||
Amplifier
|
||
\end_layout
|
||
|
||
\begin_layout Subsection
|
||
Envelope Generator
|
||
\end_layout
|
||
|
||
\begin_layout Subsection
|
||
Output
|
||
\end_layout
|
||
|
||
\begin_layout Chapter
|
||
Building a Modular Synthesizer
|
||
\end_layout
|
||
|
||
\begin_layout Section
|
||
Introduction
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
It is relatively easy to find circuits to construct simple oscillators and
|
||
filters based on the fairly comprehensible concepts of resonant circuits
|
||
and RC blocks.
|
||
Some of these concepts will be covered later.
|
||
However, as their flexibility and capabilities increase (e.g.
|
||
controlling the frequency of an oscillator with 1 volt per octave), the
|
||
circuits tend to get exceedingly complex, requiring solid expertise in
|
||
electronics.
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
This is why it was decided to switch to the usage of pre-designed, professionall
|
||
y manufactured circuit boards for this project as opposed to elaborating
|
||
all the circuits on perf boards as originally intended.
|
||
This made the goal of intermodular controllability attainable more easyily.
|
||
The downside of this approach are higher costs for boards and parts.
|
||
However, the quality of the end-product is impressing.
|
||
Also the time saving using this strategy is not to be underestimated.
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
During the research phase of this project the author found out about a modular
|
||
synthesizer building workshop taking place in berlin monthly.
|
||
It is organized by a spanish collective from barcelona called
|
||
\emph on
|
||
befaco
|
||
\emph default
|
||
(http://befaco.org/).
|
||
At the workshop it was possible to acquire various module kits containing
|
||
all necessary parts and also receive tips and support while assembling
|
||
them.
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
Since the budget for this project was limited, it was tried to arrange a
|
||
smaller setup that would still offer lots of sound design possibilities.
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
\begin_inset Note Note
|
||
status collapsed
|
||
|
||
\begin_layout Plain Layout
|
||
Befaco, help, how well it is documented is important, why the filter was
|
||
chosen, limited budget
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Section
|
||
Formats and Interfaces
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
There are several formats for module sizes, power supply plugs or patchchord
|
||
connectors which emerged out of the production lines of various module
|
||
manufacturers.
|
||
For example Doepfer's modules are only compatible with their EuroRack cases,
|
||
with a height of 128.5mm.
|
||
These EuroRack modules use jack connectors for patching.
|
||
A different size format often used in the DIY modular synth scene is the
|
||
one the serge synthesizers use.
|
||
They use banana jack connectors instead of mini jack for patching, which
|
||
have the possibility of stacking banana connectors on top of each other
|
||
and splitting the signal without having to use a multiplier module.
|
||
For this project a combination was chosen: The modules are EuroRack size,
|
||
but using banana plugs.
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
For tuned modules it is important to consider whether they use a volts per
|
||
octave or volts per hertz characteristic.
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
Audio Signals ±5Volts
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
Buffering 1:10 impedance ratio
|
||
\end_layout
|
||
|
||
\begin_layout Section
|
||
Building and Testing
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
To get started with building electronic equipment, one has to obtain some
|
||
tools first.
|
||
This includes a soldering iron - best with adjustable temperature, a role
|
||
of quality soldering tin, a desoldering pump and pliers for cutting and
|
||
bending wire.
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
Soldering is a process of mounting electronic parts onto a circuit board
|
||
by heating up board and component and then melting the soldering tin into
|
||
the joint.
|
||
A good temperature for the soldering iron is between 300° and 350° celsius.
|
||
The iron should not be pressed onto the joint for too long, because there
|
||
is a risk of destroying the component if it is sensitive to heat.
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
\begin_inset Note Note
|
||
status collapsed
|
||
|
||
\begin_layout Plain Layout
|
||
Research beginnings - Easy oscillation circuits.
|
||
easy filters.
|
||
how voltage controlled is the problem.
|
||
How it had been decided not to design all circuits self, but instead use
|
||
predesigned circuit boards in order to be able to get tuning stability
|
||
and volt-per-octave possibilities.
|
||
\end_layout
|
||
|
||
\begin_layout Plain Layout
|
||
It had been understood how designing circuits requires years of work and
|
||
experience.
|
||
\end_layout
|
||
|
||
\begin_layout Plain Layout
|
||
Module decicion, Getting the Circuit boards, Soldering, Getting Parts, General
|
||
about parts (capacitors and resistors)
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
Oscilloscope, Multimeter, Tracking faults, measuring
|
||
\end_layout
|
||
|
||
\begin_layout Section
|
||
Power Supply and Case
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
For the power unit a universal power supply circuit was chosen from an audio
|
||
circuit technology book (Sontheimer, 2004, p.
|
||
74) and mounted onto a perf board.
|
||
Instead of the 7815 and 7915 voltage regulator ICs the 7812 and 7912 were
|
||
used in order to get a ±12 volt power supply with a center tap for the
|
||
ground.
|
||
The modules can be connected to the four male 16-pin flat ribbon connectors,
|
||
that were added to make the power supply compliant to the EuroRack standard.
|
||
Another possibility would be to make a flying bus board by attaching those
|
||
connectors to a flat ribbon cable that lies in the case.
|
||
Or even just fix female connectors to the cable and plug them directly
|
||
into the modules.
|
||
Additionally it is planned to add an IEC socket and a power switch to it
|
||
for more comfortable on and off switching and more steady starting current.
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
The case is a simple rack constructed from a few pieces of wood that are
|
||
held together by 19 inch rails equipped with thread rails to fasten the
|
||
modules.
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
pagebreak
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Section
|
||
Frontpanels
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
\begin_inset Wrap figure
|
||
lines 0
|
||
placement R
|
||
overhang 3in
|
||
width "22text%"
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
vspace*{-2em}
|
||
\end_layout
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
begin{center}
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Plain Layout
|
||
\begin_inset Graphics
|
||
filename graphics/output-module-panel.pdf
|
||
scale 60
|
||
|
||
\end_inset
|
||
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Plain Layout
|
||
\begin_inset Caption
|
||
|
||
\begin_layout Plain Layout
|
||
Output module template
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Plain Layout
|
||
\begin_inset ERT
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
end{center}
|
||
\end_layout
|
||
|
||
\begin_layout Plain Layout
|
||
|
||
|
||
\backslash
|
||
vspace*{-2em}
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
The panels for all modules were made from pre-cut aluminum plates with a
|
||
white varnish.
|
||
The labels for knobs and banana sockets are printed on the plates with
|
||
a method, that is similar to homemade circuit board etching.
|
||
A mirror-inverted label template is printed onto a piece of high gloss
|
||
paper for inkjet printers - but with a laser printer.
|
||
It is cut and placed face down onto the upper side of the panel.
|
||
By thoroughly pressing down a hot flat iron (for ironing clothes) onto
|
||
the panel for a few minutes, the toner cartridge particles move to the
|
||
panel.
|
||
The paper residues need to be removed by placing the panel in some water
|
||
and rubbing them off with a sponge.
|
||
Afterwards the panel is sealed with transparent lacquer.
|
||
Once the panel is dried, the holes for the knobs, switches, etc.
|
||
can be prepunched and drilled.
|
||
Lastly all borholes are deburred.
|
||
|
||
\begin_inset Note Note
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
foto vom frontpanel ohne stecker
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Section
|
||
BF-22 Filter
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
This module is an extended copy of the filter from the legendary Korg MS-20
|
||
and is based upon the principle of the sallen and key filter.
|
||
It combines two linkable filter stages in one module.
|
||
Each stage features cutoff and frequency knobs, as well as several voltage
|
||
control inputs for cutoff frequency and resonance, whereas the cutoff frequency
|
||
input can be attenuated and inverted with one knob representing modulation
|
||
depth (labeled: ×-1 ...
|
||
0 ...
|
||
×1).
|
||
The HP/LP switch determines, if the filter is used in high pass or low
|
||
pass mode.
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
When turning resonance up, at one point the filter begins to self-resonate
|
||
at the given cutoff frequency, which means that the filter can also be
|
||
used as an oscillator.
|
||
Therefore a volts per octave input for the cutoff control voltage was added,
|
||
to be able to control the oscillating frequency in a musical context.
|
||
A look at the oscilloscope shows a sine like waveform with few overtones.
|
||
Turning the resonance to the maximum, the filter goes into distortion and
|
||
the wave becomes more square causing the sound to get more rough.
|
||
The amount of distortion is visually represented by a red LED.
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
\begin_inset Note Note
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
beispiel patch mit foto und beschreibung
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Section
|
||
Midi Input
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
Note Source
|
||
\end_layout
|
||
|
||
\begin_layout Section
|
||
Output
|
||
\end_layout
|
||
|
||
\begin_layout Chapter
|
||
Conclusion
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
describe the journey, discribe the difference and natururality of analog
|
||
sound as opposed to the digital, which i only knew before.
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
tweaking knobs to borders where the outcome is on a threshold resulting
|
||
in unpredictable patterns.
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
Thanks to Eddi, Derek, Befaco, Richard, David
|
||
\end_layout
|
||
|
||
\begin_layout Section*
|
||
List of figures
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
\begin_inset CommandInset bibtex
|
||
LatexCommand bibtex
|
||
bibfiles "synth_bibliography"
|
||
options "karl-second4"
|
||
|
||
\end_inset
|
||
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Chapter*
|
||
Declaration of academic honesty
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
I hereby declare that in the attached submission I have not presented anyone
|
||
else’s work, in whole or in part, as my own using only the admitted resources.
|
||
Where I have taken advantage of the work of others, I have given full acknowled
|
||
gement.
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
My signature below constitutes my pledge that all of the writing is my own
|
||
work, with the exception of those portions which are properly documented.
|
||
|
||
\end_layout
|
||
|
||
\begin_layout Chapter*
|
||
Appendix
|
||
\end_layout
|
||
|
||
\begin_layout Standard
|
||
\begin_inset Note Note
|
||
status open
|
||
|
||
\begin_layout Plain Layout
|
||
urs hegemann
|
||
\end_layout
|
||
|
||
\begin_layout Plain Layout
|
||
future audio workshop - cycle oder circle synthe
|
||
\end_layout
|
||
|
||
\end_inset
|
||
|
||
|
||
\end_layout
|
||
|
||
\end_body
|
||
\end_document
|