483 lines
27 KiB
TeX
483 lines
27 KiB
TeX
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\begin{document}
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\title{Experimental Music\\Summative Assignment 2\\Essay}
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\subtitle{\LARGE{The role of electronic feedback and amplification in
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experimental music composition.}}
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\author{Sam Perry\\U1265119}
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\date{}
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\begin{abstract}
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The use of electronic feedback as a tool for musical composition has
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featured in many compositions, popular for it's complex, volatile and
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indeterminate nature. Intrinsic to the use of feedback is the use of
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amplification, capable of artificially altering an input's energy, as a
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method for feedback control. This essay aims to provide a definition of
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these tools in their different forms, and to analyse their use in a
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range of prominent compositions. Forms of feedback will be defined,
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followed by a discussion of the musical implications of their use,
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including the consideration of aspects such as process, indeterminacy,
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spectral implications and rhythmic implications. This will be related
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to a number of compositions in order to provide an overall
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understanding of their role in experimental music composition.
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\end{abstract}
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\maketitle
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\section{Defining feedback and amplification}
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A simple definition of feedback is the process of routing the output of a
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system back to the input of that system.~\parencite[p.1]{weisert2010ioi}
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This can take many forms in the context of music. Whether it is the acoustic
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feedback created by aiming a microphone to it's amplifier, or the digital
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feedback present in an IIR filter, in all cases a loop is created from an
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output point of a system, back to it's input.\\
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The two types of feedback to be discussed are:
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\begin{itemize}
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\item{Acoustic Feedback}
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\item{Electronic Feedback}
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\end{itemize}
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In order to fully understand feedback, electronic amplification will also
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be explored due to it's integral part in feedback system control.
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\subsection{Acoustic Feedback}
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Acoustic feedback occurs when a closed loop is created between an audio
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transducer (such as a microphone or guitar pick-up) and amplifier,
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causing previously amplified audio to be re-amplified continuously at an
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exponential rate, as illustrated in Figure~\ref{acoustic_feedback}.
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\begin{figure}[H]
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\makebox[\textwidth]{\includegraphics[width=0.75\textwidth]{acoustic_feedback_diagram}}
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\caption[Caption for LOF]{Acoustic Feedback Diagram\protect\footnotemark}
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\label{acoustic_feedback}
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\end{figure}
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\footnotetext{Diagram taken from:~\parencite[p.185]{holmes2012eaem}}
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The volatile and unpredictable nature of acoustic feedback has been used to
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great effect in both popular and avant-garde
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music.~\parencite[p.186]{holmes2012eaem} Pioneering guitarists such as Jimi
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Hendrix have used the loop created through placing an electric guitar
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pickup close to it's amplifier to compliment virtuosic guitar solos in
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pieces such as Foxey Lady~\citeyearpar{hendrix1967fl}. This is taken one
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step further in avant-garde works such as Steve Reich's Pendulum Music,
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where feedback becomes the focus of the piece entirely. This is discussed
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further in section~\ref{pendulum}
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\subsection{Electronic Feedback}
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Electronic feedback takes the principal of recursively feeding an output
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back into an input into the analog electronics domain. In this situation,
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the recursive processing is performed purely on electrical signals,
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replacing the initial acoustic input from the microphone found in acoustic
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feedback, with a purely electronic input as part of an electronic circuit.
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The result of this process is then produced in the listening space via
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amplification~\parencite[p.187]{holmes2012eaem}. Composers such as David
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Tudor and Gordon Mumma explore these techniques through their creation and
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use of custom electronics designed to exploit the characteristics
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of this effect.~\parencite[p.186, 390]{holmes2012eaem} A detailed analysis
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of these techniques are presented in section~\ref{ElecFeed}
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\subsection{Amplification}
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Amplification is the process of scaling a signal by a chosen factor.~\parencite[p.3-4]{kadis2012sosr}.
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This artificial modification of amplitude has a number of interesting sonic
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effects in itself, as it allows for the magnification of sounds that may not
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naturally be perceivable and conversely, the reduction of extremely loud
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sounds to a comfortable range for hearing. This is explored through
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works such as John Cage's Cartridge Music as discussed in
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section~\ref{amp}\\
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It has been stated that feedback is difficult to control. This is due to
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it's recursive nature and the tendency for output that exceeds unity gain
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(a state, whereby the output amplitude of a feedback system is equal to
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that of it's input) to be fed back into the system. Amplification is
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therefore a crucial element for controlling the results of a feedback
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system. By attenuating an output before feeding it back to a system, it is
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possible to ensure that outputs do not grow at an exponential
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rate.~\parencite[p.71-72]{zolzer2011dafx}
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\begin{figure}[H]
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\makebox[\textwidth]{\includegraphics[width=0.75\textwidth]{IIR_flow_diagram}}
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\caption[Caption for LOF]{Basic Feedback Signal Flowchart\protect\footnotemark}
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\label{feed_flowchart}
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\end{figure}
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\footnotetext{Diagram adapted from:~\parencite[p.72]{zolzer2011dafx}}
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\begin{figure}[H]
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This can be demonstrated mathematically using the following example equation
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for a feedback system as illustrated in figure~\ref{feed_flowchart}~\parencite[p.70-72]{zolzer2011dafx}:
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\begin{align*}
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& y(n) = x(n) + gy(n-M)\\
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& \text{where:}\\
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& x\text{ is the input signal}\\
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& y\text{ is the output signal}\\
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& n\text{ is the current point in time}\\
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& M\text{ is the signal delay in time}\\
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& g\text{ is the feedback coefficient}\\
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\end{align*}
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\end{figure}
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\section{Musical Aspects and Implications of Feedback Systems}
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There are a number of interesting musical implications when using feedback
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and amplitude adjustment as a compositional tools. Features such as
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indeterministic and rhythmic characteristics, inherent to the nature
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of feedback, make it an interesting technique for musical exploration and
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there are many examples of artists exploiting these qualities in
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experimental compositions. Likewise, amplitude modification offers a number
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of compositional possibilities for both the control of feedback and for
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creative effect in of itself. This section outlines some of the key musical
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aspects of feedback and artificial amplification and provides examples of
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notable compositions that demonstrate these principals.
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\subsection{Indeterminacy}\label{indeterminate}
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Indeterminacy is related to the use of chance operations in music
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composition and performance. Techniques that involve a degree of
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uncertainty, where external variables or unpredictable factors affect the
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outcome, are defined as indeterminate. Simms uses the following definition
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for indeterminacy:
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``Any part of a musical work is indeterminate if it is chosen by chance, or
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if its performance is not precisely
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specified.''~\parencite[p.357]{simms1986mtc} It is a topic of interest for
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experimental composers for a number of reasons.
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\subsubsection{Variation in Performance}\label{variance}
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Using indeterministic processes as part of a composition allows for
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variation in the performance of said composition on a case by case basis.
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Through the addition of random factors to a composition, far greater
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degrees of variance are created in the performance of a piece, allowing for
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an infinite number of possible versions as opposed to the comparatively
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limited interpretation of static compositions where all elements are
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controlled directly by the composer.~\parencite[p.97-98, 381]{jc2009co,
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holmes2012eaem}
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This variance can take many forms dependant on the indeterministic factor.
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An example might be the performer, which is demonstrated well through
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Cornelius Cardew and Christian Wolff's compositions for the Fluxorchestra.
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By composing ``unambiguous, concrete proposals (which still left room for
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personal idiosyncrasies in realization)'', indeterminicity was created
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through the skill and interpretation of the performers in pieces such as
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``Stones'' by Wolff or ``The Great Learning'' by
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Cardew~\parencite[110]{nyman1999em}\\
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In terms of feedback, variance in feedback will depend primarily on the
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variance of the input to the system and the variance of control. Due to the
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non-linear fashion in which feedback effects input to produce an output,
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subtle changes in these may result in significant changes to the output. An
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example of this is a guitarist using an amplifier to produce feedback from
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his guitar. In each performance, the subtle changes in distance between the
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guitar and amplifier may result in significant differences to feedback
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tone. This property of feedback applies to compositions such as Steve
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Reich's Pendulum Music and Gordon Mumma's Hornpipe, discussed in
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section~\ref{pendulum} and section~\ref{hornpipe}.
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\subsubsection{Bias Removal}
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Indeterminacy is able to remove personal bias and ego involved in decision
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making from a composition or performance. By leaving compositional
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decisions to chance, it is ensured that the music produced is not created
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with intent and is separated from the composer's personal taste, as stated
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by John Cage~\parencite[p.381]{holmes2012eaem}. This technique is used in
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his composition ``Music of Changes'', where chance operations are used for
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the organisation of material in such a way that ``bypassed a reliance on his
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aesthetic judgement''. By combining this relinquished control with the
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precise control of other aspects of the piece, Cage was able to create a
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``balance between rational and irrational'' through the combination of
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control and total removal of control over compositional
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elements~\parencite[p.97-98]{jc2009co}.\\
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In relation to feedback directly, the ability for feedback to create
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exponentially complex output from relatively simple feedback systems
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create clear elements of indeterminacy through the unpredictability of
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their output. This is demonstrated in Steve Reich's ``Pendulum Music'' as
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discussed in section~\ref{pendulum}. Parallels can be drawn between John
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Cage's use of indeterminacy to dictate organizational aspects of ``Music of
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Changes''~\citeyearpar{cage1951mfc} with Steve Reich's use of feedback to dictate sonic events in
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``Pendulum Music''.\\
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Feedback builds on methods such as Cage's use of the I Ching as far greater
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quantity of unpredictable events can be generated quickly, compared to the
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manual ``brute-force'' approach of generating each event as is the case
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with the I Ching.
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\subsection{Process and Control}
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The term ``process'' refers to the situation outlined by a composer,
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designed for the creation of sound. Where popular music focuses on creating
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pre-defined musical content and structure, experimental musicians typically focus on
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the creation of a process through which sound may be generated. This may
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involve the creation of rules or instructions that outline the conditions
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that are needed in order to create an outcome, the content of which may
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differ on each performance based on any indeterministic factors (see
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section~\ref{indeterminate}) There are many forms of process used for the
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composition of experimental music. These are observed in detail in
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\textit{Experimental Music - Cage and
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Beyond}~\parencite[p.4-14]{nyman1999em}
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\subsubsection{Feedback Process}
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Feedback is concerned mainly with electronic process, where an electronic
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system is defined/set up in order to facilitate the creation of sound. The
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specified setup will therefore have a direct impact on the outcome of the
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piece, combined with other factors such as the methods used for control of other
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processes involved in the piece's realisation. This is true of Gordon
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Mumma's Hornpipe~\citeyearpar{mumma2002lem} (as detailed in
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section~\ref{hornpipe}) where electronic circuitry is designed specifically
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to explore the effects of using custom electronic circuitry to produce
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controlled feedback~\parencite[p.8, 390]{nyman1999em}
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\subsubsection{Feedback Control}
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As stated previously, feedback can be difficult to control due to it's
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indeterministic properties. The complex and intricate outputs possible with
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even the simplest of feedback systems causes results to differ
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significantly based on the exact conditions of the system. The two most
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significant factors that affect a basic feedback system are:
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\begin{itemize}
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\item System input
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\item System parameters
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\end{itemize}
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\paragraph{System Input}\mbox{}\\
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As with most systems, an alteration to the input of the system will result
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in the alteration of the output. This is generally true of feedback systems
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as, for example, providing an electronic feedback circuit with a louder
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input will most likely result in a louder output. This relationship may not
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be linear and depends on the design of the feedback system, which in turn
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dictates the indeterministic nature of these
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systems~\parencite[p.19-27]{weisert2010ioi}. However, it still provides a
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method for control over the output of the system. This is apparent in
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Mumma's Hornpipe~\citeyearpar{mumma2002lem} where the performer must adapt
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the input to the system (in this case the sound produced by the French
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horn) in reaction to the electronic sound produced by the ``cybersonic
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console''.
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\paragraph{System Parameters}\mbox{}\\
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As stated above, the design of the feedback system will determine it's
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response to a given input. A common method for controlling the design of a
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feedback system is through the implementation of variable nodes for the
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dynamic adjustment of parameters.~\parencite[p.19-27]{weisert2010ioi}
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A clear example of this is the use of a scaling factor in the feedback loop
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to parametrize the regenerative/degenerative nature of the system. By
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altering this parameter, the degree to which a signal is
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amplified/attenuated on each recursion can be modified dynamically during
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performance. This would be attributed to the guitar-amplifier distance in
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the typical guitar feedback example mentioned in section~\ref{variance}
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\subsection{Rhythmic/Temporal Implications of Feedback}
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The process of feeding a signal back through a system has consequences in
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terms of a subsequent iteration's rhythms. The superposition of signals
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causes alterations in the temporal content of the subsequent signals,
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resulting in the removal and addition of temporal peaks to the signal (a
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signal's peaks are linked to the perceived characteristic of the signal's
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rhythm). The effects of feedback are discussed at length with regards to
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Alvin Lucier's ``I am sitting in a room'' by
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Weisert~\parencite[p.64-68]{weisert2010ioi}. The rhythmic impact of a
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feedback system is complex. However, at a basic level, it should be
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understood that feedback causes a shift in rhythmic content over time. The
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exact rhythmic alteration is dependant on factors such as the feedback
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system, input signal and it's relationship with the subsequent iterations
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of itself. This is explored extensively in David Tudor's Pulsers (see
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section~\ref{tudor})
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\subsection{Spectral Implications of Feedback}
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As with rhythmic content, feedback has a complex effect on the spectral
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content of a signal. As with the rhythmic content, the effect of
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superposition on the original signal emphasizes and reduces spectral
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content. This is again, examined at length in Weisert's analysis of ``I am
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sitting in a room'' and a similar shift in spectral content can be observed
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to that of the rhythmic content over
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time.~\parencite[p.60-64]{weisert2010ioi}
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\subsection{Dynamic Implications of Artificial Amplitude Adjustment}
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The artificial adjustment of audio amplitude is an important technique as it
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allows for the alteration of a signal's energy. This acts as a form of
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sonic magnifier, able to make inaudibly small sounds audible, as
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demonstrated in pieces such as John Cage's ``Cartridge
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Music''~\citeyearpar{cage2013cm} and Stockhausen's ``Mikrophonie''
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collection~\citeyearpar{stockhausen1995mmt}. This technique was instrumental in the
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development of electroacoustic music by artists such as Cage and
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Stockhausen as it allowed the details of quiet sounds to be amplified
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artificially in a live environment.~\parencite[p.351-352]{holmes2012eaem}
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This process is combined with the principals of a feedback system in order
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to provide control to a feedback system. By altering the amplification of
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signals in a feedback system, dynamic control of feedback properties is
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possible. This is clearly used in works such as Robert Ashley's ``The
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Wolfman'' in order to tune the feedback in an appropriate
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fashion.~\parencite[p.186]{holmes2012eaem}
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\section{Composition Analysis}
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There are a large number of pieces that utilise electronic feedback and
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amplification creatively. This section analyses some of the most prominent
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pieces in order to present some explorations and usages of feedback in
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experimental music.
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\subsection{Amplification}\label{amp}
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\subsubsection{John Cage's Cartridge Music~\citeyearpar{cage2013cm}}
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Cartridge music explores the amplification of small sounds through the use
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of phonograph cartridges and a range of object in order to create amplified
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audio based on the performer's interactions with these objects. By
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inserting the object in place of the phonograph's needle, a performer is
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able to create amplified sounds that vary based on the type of object used.
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This piece was created to explore the possibilities of amplifying small
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sounds to within an audible range and the chance sounds that are created as
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a result. The piece focuses on the aesthetics of different mediums of
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object, and does not concern itself with player improvisation as do other
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examples. This reflects Cage's attitude towards the process and openness to
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chance events by allowing the unexpected to form part of the piece, without
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intervention of the performer.~\parencite[p.56-61]{lucier2012m109}
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\subsection{Acoustic Feedback}
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\subsubsection{Steve Reich's Pendulum Music~\parencite[p.31]{reich2002wom}}\label{pendulum}
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This piece is possibly one of the most direct explorations of acoustic
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feedback. Where other pieces explore the effects of feedback on/with an external source,
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Pendulum Music focuses directly on the sonic phenomena generated purely by
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the feedback system and the acoustics of the space~\parencite[p.50-51]{weisert2010ioi}.
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Aesthetically, the piece begins with clear rhythms created by the distinct
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motion of the microphones as they pass over the speakers. This slowly
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degrades as the microphones lose momentum, resulting in the pure feedback
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tones created as the microphones hang motionless over the speaker at the
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end. Interesting phase relationships can be observed between the
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microphones as the piece progresses, which is in keeping with Reich's works
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such as Come Out~\citeyearpar{reich1966comeout}
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This piece has a clear focus on process and was described as ``the ultimate
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process piece'' by Reich. Realised as an ``audible sculpture'', the piece is
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designed to limit human interaction in order to focus on the natural
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interaction of acoustic feedback. Control of aesthetics is determined by
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the semi-indeterministic method of releasing the suspended microphones,
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then allowing natural swinging motions to dictate sonic events and rhythms.
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This process is described as semi indeterministic, as it is clear that the
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microphones will swing back and fourth at diminishing amounts over time,
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however the audible feedback, interplay between audible events, feedback
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tone etc\ldots are largely left to chance. This created a stark contrast
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between the compositional process and chaos process presented through the
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uncontrolled feedback~\parencite[p.186]{holmes2012eaem}.
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This piece fits in with reich's other work through it's exploration of theme
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such as audio phaseing and rhythm, similar to that of his works such as Come
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Out~\citeyearpar{reich1966comeout} and Clapping Music~\citeyearpar{reich1966clap}
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\subsubsection{Robert Ashley's The Wolfman~\citeyearpar{ashley2003w}}\label{wolfman}
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The Wolfman explores a number of aspects of acoustic feedback through the
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use of vocalisms for the control of tape sample modulated feedback. By
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creating even small vocal sounds, the performer is able to control the
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aesthetics of the feedback loop demonstrating the exponentially complex
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impact of even the simplest inputs to a feedback system, as described
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previously. Ashley commented that ``the vocal sounds used to induce the
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feedback have to be extremely soft so as not to block it'' and he regretted
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that the piece was believed to be generated by screams, which was far from
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true~\parencite[p.37]{gann2012ra}. The result is a massive build up of
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distortion and noise that develops as more vocalisms are supplied to the
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feedback loop. It has also been observed that the piece's spectral content
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is largely dictated by the room acoustics, tending towards a build up of
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high pitched, shrill tones in smaller rooms. This shows the general focus
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on the concept of process in experimental
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compositions~\parencite[p.18]{cage2011silence} as the piece may differ
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dramatically based on the conditions of the performance.
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\subsection{Electronic Feedback}\label{ElecFeed}
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\subsubsection{David Tutor's Untitled~\citeyearpar{tudor1996twfle} and Pulsers~\citeyearpar{tudor1996twfle}}\label{tudor}
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Tudor's Three Works for Live Electronics aimed to explore the creative
|
|
possibilities of using live electronics for composition. This was achieved
|
|
by creating custom electronic circuitry for the generation, manipulation
|
|
and feedback of audio. This was then controlled through the live filtering
|
|
and amplification of the feedback circuits to alter the output over
|
|
time~\parencite[p.187]{holmes2012eaem}.
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|
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|
\paragraph{Pulsers}\mbox{}\\
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|
Pulsers aimed to explore the temporal and rhythmic effect of feedback and
|
|
live electronics by using extensive electronic feedback/amplification
|
|
networks to modify the sound of various materials such as a tape recording
|
|
of an electronic violin~\parencite{tudor1984twle}. By altering the amplification and filtering of the
|
|
circuit live, the performer is given control over the rhythmic aspects of
|
|
the output. This results in the controlled use of the complex rhythms
|
|
possible with feedback.
|
|
Pulsers focused primarily on the aesthetic potential of manipulating analog
|
|
circuitry, particularly on the rhythmic impact of altering analog
|
|
components.
|
|
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|
\paragraph{Untitled}\mbox{}\\
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|
Untitled was created as an exploration of the use of ``no-input'' live
|
|
electronics. The electronic setup consisted of a complicated feedback setup
|
|
designed to manipulate the characteristics of sounds created purely through
|
|
the electronics (without any external input from microphones or
|
|
recordings).
|
|
The live adjustment of electronic parameters created an interesting
|
|
improvisational element in Untitled, as the complex nature of the
|
|
circuitry created an interplay between performer and the system. The
|
|
performer would adjust parameters, the system would respond, and subsequent
|
|
alterations would be made as a result~\parencite{tudor1984twle}.
|
|
However, the tendency for feedback to become uncontrollable and the
|
|
extremely complex signal path resulted in a piece too complex to be
|
|
manageable in terms of live performance. This is a good example of the
|
|
indeterminate, complex nature of
|
|
feedback.~\parencite[p.83-85]{weisert2010ioi}
|
|
This piece served as an attempt to explore the musical possibilities
|
|
created purely from the sound of the electronics themselves. This differed
|
|
from the conventional use of electronics to alter an external sound created
|
|
by an oscillator or external audio source.~\parencite{tudor1984twle}
|
|
|
|
\subsubsection{Gordon Mumma's Hornpipe~\citeyearpar{mumma2002lem}}\label{hornpipe}
|
|
Hornpipe is a composition that combines the input from a French horn with
|
|
custom electronic circuitry created by Mumma, in order to transform the input by
|
|
monitoring and altering output based on input resonance.
|
|
The piece aims to explore electronic circuitry as a form of extension to
|
|
the horn, as electronic characteristics are dependant on the input from the
|
|
horn and the acoustic space in which the piece is
|
|
performed.~\parencite[p.101-103]{nyman1999em}
|
|
This piece demonstrates a combination of electronic and human process as
|
|
the sound produced by the electronic circuitry's interplay with the human
|
|
improvisation in reaction creates the final result.
|
|
The piece also explored the indeterministic aspects of feedback due to the
|
|
unpredictability of the electronic circuitry based on the number of factors
|
|
that determine it's output.
|
|
|
|
\section{Conclusion}
|
|
It is clear that feedback provides enormous potential for creative
|
|
possibilities in music, as demonstrated by the wide variety of
|
|
experimental compositions detailed. This is far from an exhaustive set of
|
|
examples and many more examples explore the unique properties of feedback.
|
|
Overall, feedback's indeterministic nature, spectral/temporal impact, and
|
|
range of possibilities for control make it a unique and interesting area
|
|
for musical experimentation.
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|
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|
\printbibliography
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\end{document}
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