Composition Processes

G. M. Koenig

By musical composition we generally understand the production

of an instrumental score or a tape of electronic music. However,

we also understand composition as the result of composing:

the scores of instrumental or electronic pieces, an electronic

tape, even a performance (we say for instance:  "I have heard a

composition by composer X"). The concept of composition is

accordingly closed with regard to the result, but open with

regard to the making of a composition; it tells us nothing about

preparatory work, whether it is essential for the composition

or not. Preparatory work includes the choice of instruments and

values for dynamics or durations, but it also includes the

definition of sounds in electronic music and can even be extended

to cover the invention of special graphic symbols. Electronic

sounds or graphic symbols are not always additions to composition;

they are often "composed" themselves, i.e. put together according

to aspects which are valid for actual composing.

These considerations give rise to the following questions:

     what do we mean by "composition"?

     do we mean the composition of musical language structures?

     do we mean the composition of sound structures?

     do we mean the composition of single sounds?

To begin with the last one: can we call a single sound, especially

in electronic music, a "composition" or at least the result of

composing? In the early days of electronic music the Cologne studio

stressed the fact that not just a work but each of its individual

sounds had to be "composed"; by this they meant a way of working

in which the form of a piece and the form of its sounds should be

connected:  the proportions of the piece should be reflected as it

were in the proportions of the individual sounds.  It is better

to call a list of sound data having no direct connection with

the structure of a piece a description of the sounds.  In terms

of Cologne aesthetics it is then perfectly possible to talk

about the composition of single sounds, but this brings us to

the next question as to what a single sound is. The term comes

from instrumental music, where it is most closely involved with

questions of performance and notation technique. To give a

tentative and rough description of the single sound, it is

characterized by an unmistakable start ("entry") and an un-

mistakable end and consequently by an unmistakable duration,

furthermore by uniform pitch, loudness and timbre. We can specify

this rough description in more details by the following remarks:

- timbre changes in the single sound play such a slight part as

  to be negligible here,

- changes of loudness in the single sound (crescendo, decrescendo,

  tremolo) generally belong to performance or expressive charac-

  teristics, the above definition (start, end, duration and

  pitch) being unaffected; sounds starting "inaudibly" pp or

  "dying away" to pp are exceptions which are justified by the

  general redundance of the context,

- pitch-changes in the single sound (glissando) restrict the

  above definition more closely; we might however take into

  account the fact that glissandi frequently occur as mere

  transitions between stationary sounds (especially for singers

  and string-players), and that independent glissandi contra-

  dicting harmonic unambiguity, form, like pitchless percussion

  sounds or clusters, a category of their own in which the

  conditions of beginning, end and duration are still valid.

As this definition shows, we can only speak of single sounds in

instrumental music really (and even then only within limits)

and in the first phase of electronic music, which was closely

linked with instrumental traditions.  In the ensuing period of

electronic music it is better to speak, instead of the composition

of single sounds, of the composition of sound-events or even

sound-fields, since a sound-event is not only assembled from

pitches, degrees of loudness and durations, but includes to an

increasing extent transformations as well: the uniform composition

of an event frequently results in an auditory impression whose

variability contradicts the definition of individual sound in

various parameters; the beginning, end and duration are all that

are left of the definition. These quantities also describe the

entire work,  though, which might consequently be seen as a single,

complexly modulated sound. As we see, considerable difficulties

can be involved in making a distinction between a composition

and its individual sounds, so that we can only answer the

question as to whether we should understand composition as the

composition of single sounds in the affirmative when there is

a continuous structural connection between the overall form and

its parts, right down to the physical sound data, and only then

when - in the sense of instrumental tradition - the whole can

be heard to consist of individual parts.

Detailed discussion of the single sound has shown that it is

only covered by the term composition to a limited extent. The

composition of sound structures seems to fit into our subject

more appropriately. This is because in sound structures physical

sound data and musical structural quantities meet. The sound

structure is not tied to the narrow definition of the individual

sound, but may, as we have seen, consist in the auditory im-

pression of single sounds. According to its definition the sound

structure is more complex and usually longer than a single

sound, thus more closely approaching a form-section, virtually

the whole work. Nonetheless the sound structure can also be said

to cover a partial aspect of composition: it would either have

to be described as a more complex, assembled single sound or as

an unfinished piece. However, the technical circumstances of

working in an electronic studio or with a computer often lead

to composing in sections; problems of sound structure can there-

fore be treated just as well under the musical structures of

entire pieces.

This brings us to the last of the questions posed before: by

composition   processes do we mean the composition of musical

language structures? Emphatically, yes. Composing terminates

in pieces, and the extent to which pieces are put together from

sounds, and the relations prevailing among these sounds, are a

matter of how a composer works. Composition is the application

of a grammar which generates the structures of a piece, whether

the composer is aware of an explicit grammar or not. The sound-

elements (I leave the question open as to whether these are

single sounds or sound-events) to be composed into structures

do not have to be in an unambiguous relationship either to one

another or to the structures; assembly - "composing" - always

takes place when something big consists of smaller parts. In

more simplified terms, then, we can say that composition refers

to elements which need not themselves be the subject of com-

position; the consideration of composition processes can dis-

regard questions of sound production; sound production is not

interesting as a composition process until it becomes integral,

i.e. until the structure-generating grammar refers to sound data

instead of to given sound elements.          .


We are faced with a distinction between structure and sound as

soon as a composer not only writes a score but makes a sonic

realization of it as well. This occurred for the first time in

electronic music when not only single sounds but entire sound

structures could be produced, particularly with the aid of

voltage control. The compositional rules for giving form to the

individual events as well as for connecting them in time were

notated in wiring diagrams which could be reproduced to a

certain extent in the form of studio patches. Not until digital

computers were used did it become possible however to execute

compositional rules of any desired degree of complexity, limited

only by the capacity of the computer. Automatic realization of

entire electronic pieces or at least of lengthy sections using

voltage control systems seems to be the exception, though, and

in the field of computer music much more attention appears to

be paid to problems of sound production than to those of com-


In his article "A Composer's Introduction to Computer Music",1

William Buxton makes a distinction between `composing programs'

and `computer-aided composition'. As examples for composing

programs the article refers to Hiller's ILLIAC Suite, Xenakis'

ST programs and my own programs, Project One and Project

Though this list is not complete, it is conspicuous for its

brevity. A reason for this might be the practical impossibility

of describing the composition process entirely in the form of

computer programs. Although a composer runs through more or

less fixed sequences of decisions determining his personal style,

and also employs consciously chosen rules limiting the freedom

of his decisions in the individual case, he is still, whether

he is aware of this or not, under the impression of a musical

tradition which values a composer's originality more highly

than his skill in using established patterns. A composer is more

accustomed to being influenced by a spontaneous idea than by

prepared plans; he decides and discards, writes down and corrects,

remembers and forgets, works towards a goal; replaces it during

his work by another - guided by criteria which are more likely

to be found in psychology than in music theory. This is why

computers are more likely to be used for purposes of composition:

(1) to solve parts of problems or to compose shorter formal

sections instead of complete pieces,  (2) to try out models greatly

simplifying compositional reality and supplying the composer

with a basic scheme which he can elaborate as he feels best, (3)

to compose an individual piece for which the composer writes a

special program more resembling a score than a solution for a

number of problems.

In the chapter on computer-aided composition, Buxton refers to

the SCORE program, MUSICOMP, the GROOVE system and the POD pro-
grams, among others.  This list demonstrates how difficult it is

to separate the actual composition of a piece of music from

auxiliary actions which are partly predominant or subordinate

in the composition, or which partly overlap. Here we are faced

by the issue of whether we are going to understand composing as

the entire process from planning via writing the  score (or pro-

ducing a tape) right up to performance, or merely as the intel-

lectual act of invention. If we limit ourselves to the intellectual

act of invention, we speak of `composing programs', of musical

grammar, of a score as a document of intellectual activity, in-

spiration, creative powers. If on the other hand we envisage the

entire process, it can be divided into a number of single

activities which can be performed by different agents: composers,

musicians, generators, computers, not to forget the listeners.

These auxiliary services include, as far as we are dealing with

computers:  (1) the sonic realization of previously fixed score

data,  (2) the processing of parts of problems using libraries

of subprograms, (3) the production of graphic scores or musical

graphics,  (4) sound production based on simple compositional

rules, so that, say, the sound models from a sound library are

assembled to form sound structures. The computer performs various

services in these examples: in the sonic realization of score

data it replaces an electronic studio or an orchestra, whilst

not being responsible for the score; dealing with parts of

problems with the help of a subprogram library can be expanded

to become a complete description of the act of composing; the

production of graphic scores replaces the copyist, a musical

graphic leaves the completion of a piece to - more or less -

improvizing players; sound production according to simple

compositional rules has the character of a model both with

regard to the sounds and to the combinatorial methods - the

same group of sounds can be subjected to different combinations

or different groups of sounds can be arranged similarly.

There are advantages and drawbacks to distinguishing composing

programs and computer-aided composition. An advantage is that in

the case of composing programs the computer is expected to supply

the compositional work, whilst in computer-aided composition

the responsibility is entirely the composer's. A consideration

of composition processes might therefore be limited to composing

programs. A drawback is that the composition process consists of

activities which cannot be separated into main and auxiliary

activities so easily; even in composing programs the composer is

still chiefly responsible because he must at least prepare the

data on which the composition process basically depends, if he

does not in fact also write the program himself. - In what follows

I shall limit myself mainly to the invention of music in the form

of representative models, without going into the distinction

between main and auxiliary actions.


We have been occupied with programmed music at the Institute

of Sonology at Utrecht University since 1965; by programmed

music we mean the establishment and implementation of systems

of rules or grammars, briefly: of programs, independent of the

agent setting up or using the programs, independent too of

sound sources. This means that programmed music covers:  (1)

instrumental scores which a composer writes at his desk on the

basis of binding compositional rules, which do not fundamentall

differ from computer programs,  (2) electronic compositions which

like the said instrumental scores are systematically composed,

then to be `mechanically', i.e. without additions and cuts,

realized on studio apparatus,  (3) electronic *works produced

automatically by the use of studio patches,  (4) instrumental

scores based on computer programs,  (5) tapes based on sound data

which were calculated and converted by a computer program. In

this field of programmed music, instrumental and electronic

pieces have been realized with and without the computer, and

for some years our lecture schedule has included a series of

lectures with this title alongside the subject of computer

sound synthesis which does of course occasionally overlap the

first one. The experience we have gained during the years and

which I assume is fairly similar to experience gained elsewhere

can be summarized as follows:

The composing process

Opinions differ as to what a composing process is, there being

all gradations between constructive and intuitive composers.

Investigations in the field of programmed music can only be ex-

pected from composers who already have highly constructive

inclinations or previous knowledge or, although keener on free

expression, want to discover a new realm of experience. Among

composers with constructive inclinations one often observes a

tendency towards processes which to a fair extent exclude com-

positional decisions made in advance, i.e. the input of

structure-conditioning data. They prefer to choose what cor-

responds to their personal taste from among the automatically

produced results. If, for instance, there is a choice between two

composing programs with differing input formats, the program

with the smaller input format is more likely to be chosen. It

is often only taken as a model for a composer's own program

which gets by with even fewer data. Syntactic rules are replaced

as far as possible by random decisions.

The other extreme occurs too, but rarely. Here composers mistrust

the automaton or chance, and try to control the process down to

the last detail. This leads to programs with large input formats,

with a detailed dialogue between composer and computer, and to

the composition and frequent correction of smaller and smallest

form-sections. We again observe here the smooth transition from

composing programs to computer-aided composition. - I am speaking

here, incidentally, of tendencies observed in composers working

at our institute, who after becoming acquainted with existing

programs go their own way and contrive their own composing

systems, occasionally taking years over them. There is no doubt

as to the popularity which systems for computer-aided composition

generally enjoy, but this is not covered by my subject.

The fundamental difficulty in developing composing programs is

indubitably in determining the dividing-line between the automatic

process and the dynamic influence exerted by the composer by

means of input data and dialogue. To put it briefly: when there

are few data and little dialogue, automata are expected to produce

the composition; when there are a lot of data and dialogue, the

responsibility remains the composer's, the computer being degraded

to an intelligent typewriter. The dividing-line between composer

and automaton should run in such a fashion as to provide the

highest degree of insight into musical-syntactic contexts in

the form of the program, it being up to the composer to take up

the thread - metaphorically speaking - where the program was

forced to drop it, in other words: to make the missing decisions

which it was not possible to formalize. The development of com-

posing programs consists of pushing this dividing-line further

and further away. Whoever goes along with this personal opinion

of mine will realize the difficulties involved in this approach.

For the attempt to formalize is not only oriented towards a

medium - music - which, as opposed to natural language tends to

unravel rather than to fix; every composer will moreover imagine

the dividing-line to be in other areas, depending on his stylistic

criteria and expressive requirements. The computer program with

which a composer is confronted may pose him a puzzle instead of

solving it.

Compositional rules

In the search for compositional rules for making composing pro-

grams, there are three main avenues:

The first one leads to the analysis of existing music of the

past and present. The premise here is that the rules, or at least

the regularities in a composer's output or in a stylistic period

can be discovered if one examines the scores closely enough.

Regardless of the use of such analyses for musicological research,

say for purposes of comparing styles or classifying anonymous

scores, the question remains as to whether it supplies the re-

quired indications for the synthesis of music. Analysis and syn-

thesis do not cover each other perfectly enough for the results

of analysis, if used productively, to lead back to significant

music; analysis proceeds from questions which are not necessarily

those of the composer; after all, in order to arrive at statements

of sufficient generality, not only must very complex questions be

formulated, but a vast number of scores be subjected to such an

analysis. The historical line of sight would at the same time be

unhistorical, because it would ignore historical development and

measure works from different periods by the same standards. One

might also ask whether a composer who wants to create something

new can benefit from frozen models from the past. In all this we

must of course not overlook the fact that knowledge of compositional

means as developed during the past centuries and exerting in-

fluence right up to the most advanced composing, is an absolute


The second avenue leads to introspection. The composer/programmer

analyses his own experiences, he investigates whether and to what

extent his way of composing is formed by habits which can be

formulated as rules. He refers tothemusic of his predecessors

from whom he learnt his craft, going as far back in history for

this as he wants. Systematic analysis is replaced by intuition,

at least as far as he discovers rule-like aspects in his models

and renders them fertile for his own work. An exchange of ideas

with colleagues, even with pupils, can be significant because

it results in a higher degree of generality. Introspection has

the drawback of being less objective and hence less generally

valid; on the other hand introspection has the advantage of

proceeding less from analytical, but more from synthetic problems;

it is aimed more directly at matters of compositional craft and

therefore does more justice to reality. Introspection also presents

an opportunity for describing compositional ideals instead of

limiting them to the recapitulation of what has gone before.

  The third avenue leads to the description of models. As long as

we do not know how musical language functions, nor see how to

derive its grammar from everything composed'up to now, we can

still assemble fragmentary knowledge and assumptions to form a

model which can tentatively represent reality. Models describe

partial aspects, and the results achieved with their help can

only be compared with partial aspects of the~reality they are

substituting. The systematic approach which makes the first way

of analysis, striving towards completeness, seem attractive,

appears here again in the form of methodical experiments. Repeated

application of a model under changed circumstances makes its

limits clearer; accumulation and correlation of the results cause

the model to reveal itself and at the same time the extent to

which it coincides with a part of musical reality. In this it may

even transcend the reality experienced up to that point by ex-

posing contexts which had escaped analytical scrutiny. The ana-

lytical task - given the music, find the rules - is reversed:

given the rules, find the music.

Compositional results

Another issue closely linked with that of rules is the compositional

result achieved with composing programs. Rules abstracted from

music by means of analysis, introspection or model construction

result primarily in the acoustic (or graphic) equivalent of this

abstraction; the relation to music has to be created again. This,

too, can be done in different ways.  I expressly mention this re-

translation because it should be already kept in mind when a

composing program is being designed. There are various ways of

doing this too; I shall deal with three of them here.

One possible evaluation is the comparison with precedents which

are to be imitated by means of the program or suitable input

data. This particularly applies to programs written on the basis

of extensive analysis of existing music. Apart from the trivial

question as to whether the program is carrying out the given

rules correctly so that the composed result contains the desired

quantities in the desired combinations, it would be good to

examine whether, when listening to the results, there is an

aesthetic experience comparable to the precedent. I use this

vague term, aesthetic experience, to designate the quality which

distinguishes, say, a written score from its performance, or a

composer's material from the constellations in which it eventually
appears in his music.

Another evaluation refers to the expectations of the writer or

user of the program. Especially in the case of the already

mentioned introspection, this does not involve reviewing existing

aesthetic products, but in a way looking forwards for ideals to

inspire a composer in his work. The result of such an evaluation

depends on goals which do not refer to precedents with which

they can be compared. This evaluation is consequently less com-

municable than the first one involving the formalizable comparison

of original and copy.

A third evaluation is to look for musically experienceable refer-

ences in a context produced by means of models. Since the model

merely marks out the framework within which aesthetically com-

municable contexts are presumed to be, the results produced by

means of the model cannot be compared with precedents, nor with

ideals. They appeal rather to the evaluator's capacity for

discovering what is special in what is general, i.e. the ac-

cumulation of what is significant in surroundings whose signi-

ficance is at the most latent. As already explained, it is up

to methodical experimentation to determine the validity-range of

the model - and thus the probability of accumulating aesthetically

communicable constellations; one must not forget that the models

only describe basic structures which will need detailed

elaboration in the form of a score or tape. - What I have been

saying here obviously also applies to the evaluation of precedents

and expectations.

Compositional methods

I shall now turn to some compositional methods which are due to

introspection or which might be useful in constructing models,

but which in any case represent generalizations of the concrete

process of composing. Note, though, that they remain within the

range of experience of the composer writing, or just using, a

computer program.

Interpolation might be a good name for a method which so to speak

pushes forwards from the outer limits of the total form into the

inner areas; applied to the dimension of time this would mean:

dividing the total duration into sections, the sections into

groups, the groups into sub-groups and so on, until the durations

of the individual sounds can be established. We could apply this

method accordingly to other dimensions too, by speaking of

aspects, partial aspects, variants and modifications.

By contrast, extrapolation would proceed from the interior

towards the outside: from the individual sound to the group of

sounds, thence to the super-groups, via sections to the total

form. Both methods are concentric; the formal shells which so

to speak enclose the nucleus of the form exist in ideal

simultaneity; the form is not unfolded teleologically but rather

pedagogically, the details being presented in such a way that

the relation of the detail to the whole is always quite clear

to the listener.

As opposed to these two methods of interpolation and extrapolation

there is a third which I should like to call chronological-

associative. The composing process unfolds along the time-axis,

thus being put in the position of the ideal listener. Note that

in this way every event is given its irremovable place in time,

whereas in the previous examples of interpolation and extrapolation

the events were interchangeable.

A combination of methods more oriented towards time or space can

be found in the composition of blocks; by a block I mean a part

of a structure which requires complementing by other blocks but

which is still complete in itself. It is easier to state rules

for blocks than for entire pieces, because they are of shorter

duration and do not have to meet the demands made on pieces.

Individual blocks can be produced by means of interpolation,

extrapolation or the chronological-associative method; their

order is determined by the composer, i.e. outside the scope of

the formalization in the program.

The chronological-associative method can finally be extended to

the teleological or goal-oriented method by means of feedback.

Here the composer supplements individual data and syntactic

rules describing only local strategy by objectives with which

local events are continually compared. This type of method

seems to approach most closely the real process of composition,

but it also involves the greatest difficulties of representation

in program structures.

Practical aspects

To close this section, I shall talk about a few practical aspects

of writing composing programs, their accessibility and the forms

of data output.

The writer of a composing program must first of all clearly

define the points of departure and goals. Points of departure

are chiefly in the relation between computer and composer, i.e.

between the musical knowledge stored in the program and the

input data the composer uses to manipulate this knowledge.

Goals are related to the extent and kind of the expected

results. The definition of the compositional method is also

important; for instance, rules, probability matrices, weighting

factors, chance etc. have to be taken into account.

The accessibility of composing programs is primarily a question

of the available computer system: how much computer time can be

given to users, either in the single-user or time-sharing mode;

furthermore it is a question of program construction: whether

input data must be read in or whether the composer in the course

of a dialogue with the computer can continually influence the

program; accessibility also depends on turn-around time, i.e.

on how long it takes for the composer to receive the output;

it is finally a question of the program language if only a sub-

program library is available and the composer has to write his

own main program.

Data is usually output in the form of tables, musical graphics

or sounds. Tables sometimes need to be laboriously transcribed

into musical notation, musical graphics are restricted to

standard notation; it is very practical to have a sound~output

of a composed text giving the composer a first impression in the

three parameters of pitch, loudness and duration, before he

decides to have tables printed or musical graphics executed.

Things are different with systems which do not produce a score

but only a sound result; the above-mentioned criteria of

accessibility play an important part here.


To round off this paper on composition processes I shall deal

in more detail with a few programs developed or in the process

of being developed at the Institute of Sonology. I shall classify

them as composing programs for language structures (instrumental

music) sound-generating programs in the standard approach, sound-

generating programs in the non-standard approach, program-

generating systems based on grammars.

Composing programs for language structures

From 1964 to 1966 I wrote a composing program myself. I regard

it as a first attempt, and therefore called it `Project One',
abbreviated in PR1.  It has had a lively history: after its first

version in FORTRAN II, tried out on an IBM 7090,   I made an

ALGOL 60 version for an ELECTROLOGICA X8 computer at the computer

department of Utrecht University. When the Institute of Sonology

acquired its own computer in 1971, I made a FORTRAN IV version

of the program for our PDP-15.. Still. a few years later, after six

VOSIM generators had been built according to Kaegi's model,  I gave

`Project One' a sound output making it possible for a composition

to be heard in the three dimensions of time, pitch and loudness.

I had the idea of collating my experience with programmed music

at the desk and in the electronic studio to form a model which

would be able to produce a large number of variants of itself

almost fully automatically. Faithful to the fundamentals of the

nineteen-fifties, all the parameters invblved were supposed to

have at least one common characteristic; for this I chose the

pair of terms, `regular/irregular'.  `Regular' means here that

a selected parameter value is frequently repeated: this results

in groups with similar rhythms, octave registers or loudness,

similar harmonic structure or similar sonorities. The duration

of such groups is different in all parameters, resulting in over-

lappings. - `Irregularity' means that a selected parameter value

cannot be repeated until all or at least many values of this

parameter have had a turn. The choice of parameter values and

group quantities was left to chance, as was the question of

the place a given parameter should occupy in the range between

regularity and irregularity. A composer using this program only

has to fix metronome tempi, rhythmic values and the length of

the composition, in other words: he only decides on the time

framework of the result, and this only roughly, because all

details are generated by the automatism of the program.

Experiments on a large scale were not made with this program,

however, because it is a laborious and time-consuming business

to transcribe the tables printed by the computer into notation;

the turn-around time was too long as well, as long as the pro-

gram was still running at the University computer centre. Not

until the program was installed on our own computer was it

possible for a composer to produce several variants in a similar

length of time and compare them; but by then I had already

written `Project Two', which I shall discuss presently, and

which allows the composer to have more influence on the composition

process.  `Project One' therefore gathered dust until - about a

year ago - we could build six VOSIM generators which play com-

posers their results in real time. The large number of experiments

which could be made in a short time revealed a second `dividing

line'; the first one, mentioned earlier, separates the independent

achievements of the program from the composer's possibilities of

influencing it. The second one, discovered with the sound results

of `Project One', separates the significance of random decisions

in the micro and macro range of the form. In my first design of PRl

I was led by the idea that since the details of the form already

depend on chance, although within certain limits, the overall

form can be subjected to chance too as long as care is taken that

the various aspects of the form described by the program are

really given the opportunity. More recent experiments with the

program have shown, however, the extent to which the rules for

the overall form affect the course of the form in detail; it

appears that the comprehension of a listener horizontally com-

bining single tones to groups of tones, groups of tones to larger

units, and vertically observing the changing structure of different

durations, pitches and loudnesses and connecting these data in

an as yet uninvestigated manner with impressions, changing in

time, of musical states, is increased when either the details

of such a state or the states themselves arouse expectations

which can be fulfilled in the further course of developments.

In order to observe this phenomenon more closely, I first created

a possibility of revising, by means of user data, the random

decisions for the overall form which had been made by the program.

The results are encouraging and indicate ways of defining more

precisely the said `dividing line' between the micro and the

macro-form. The reverse method is in preparation too, by which

the user will have greater influence on the construction of the


This work on `Project One' took up the time which I had really

intended to spend on a new version of `Project Two'. Since this

second composing program has already been exhaustively documented

in the `Electronic Music Reports', published by our Institute, I
can make do with a brief summary here.  - As I have already

mentioned, PR2 was written shortly after I had finished PR1,

about 1966 to 1968. Up to now it has run in an ALGOL 60 version

at the University computer department, and therefore suffered

from the same problems as the first project. I am at present

translating the ALGOL program into a FORTRAN version which will

be able to run on our own PDP15 and be given a VOSIM sound output.

I am also.planning an extended and improved version.

Two properties chiefly characterize `Project Two'. On the one

hand the user is expected to supply a lot of input data not only

defining the value-ranges in eight parameters but also making the

parameters interdependent; on the other hand the individual

decisions within the form-sections are not made to depend on

chance, as in PRl, but on selection mechanisms specified by the

composer. PR2, like PRl, realizes the idea of a form-model which

can be tested. in any number of variants. Both programs, PR2 more

so than PRl, require careful preliminary work from the composer,

since they are not interactive. The planned new version of PR2

will however make it possible for the computer and composer to

hold long dialogues.

Sound programs in the standard approach

The question as to composition processes inevitably leads to

that of the construction of the sounds in composed structures,

inasfar as the latter did not precede the former. In sound-

generating computer programs we distinguish, as proposed by
Holtzman,  between the `standard' and the `non-standard' ap-

proach. To quote Holtzman: "Standard approaches are characterized

by an implementation process where, given a description of the

sound in terms of some acoustic model, machine instructions are

ordered in such a way so as to simulate the sound described;

the non-standard approach, given a set of instructions, relates

them one to another in terms of a system which makes no refe?ence

to some super-ordinated model, (...) and the relationships

formed are themselves the description of the sound. Standard

systems are seen as more or less `top-down' systems where the

synthesis technique is conceived of as manipulated in terms of a

given acoustic model. In digital synthesis, programs developed

by M. Mathews, i.e. Music IV-V, exemplify the standard approach

to sound synthesis and form the basis of other major synthesis
programs, e.g. Vercoe's Music 360, Howe's Music 4BF etc.

The VOSIM sound output to PR1 and PR2 also belong to standard

systems, and so do programs for a digital hardware Fourier generator,

two digital hardware frequency modulation generators (after
Chowning's model)  and Kaegi's MIDIM system. This list should
also include Truax's POD5 and POD6,  -which there is not enough

time to examine. more closely here. I am also skipping the Fourier

generator and a program written by William Matthews for using FMS

generators. The said programs are chiefly for pure sound production

and will not be able to take part in the composition of language

structures until they are embodied in suitable composing programs.

Unfortunately I cannot say very much about Kaegi's MIDIM program,

since at the time of writing this paper his manual was not yet

available. It is based - as a sound-generating program - on the
VOSIM system   for the minimal descripti6n of speech sounds,

which has since been expanded to apply to instrumental sounds.

At the same time, however, it is a transition to composing systems,

only that here one proceeds from the sound to the composition

instead of the other way round - as far as I know, this is a unique

case. This transition is caused by having a library of instrument

definitions continuously compared with the structure-generating


 Sound programs in the non-standard approach

Among `non-standard' systems, as produced at the Institute of

Sonology, Paul Berg's `Pile' and my own SSP can be named. (Kees

van Prooijen's CYCLE program is so similar to PILE that it is

sufficient to mention it.) To clarify these I quote another

passage from Holtzman's article: "... Samples are related only

one to another, the relationships created determining the timbre,

frequency, etc.; related only one to another suggests that the

relationships are diacritically defined and do not refer to some

super-ordinate model or function. For example, given a set of

possible relationships that may exist between samples in a

digital computer, one considers the relationships only in terms

of computer instructions -  i.e. they may be related by, and only

by, machine-instructions which can alter the state of a certain

register, e.g. the accumulator. In such a system, one sample may

be related to the previous two samples as the result of their

`XORing'. The samples are conceived of in terms of machine-
instructions rather than on the basis of some acoustic theory."

Holtzman example of two samples only related by an XOR refers
to Paul Berg's PILE compiler.   The PILE language was written

following the development of more than 20 ASP programs in which

random operations, referring to the accumulator, and also

arithmetical and logical operations, were represented systematically.

The computer acts as a sound-generating instrument sui generis,

not imitating mechanical instruments or theoretical acoustic

models. PILE, which is very popular among our students, has


CONVERT, SEED and similar ones, which are translated by the PILE

compiler into the assembly language of the computer so that

students can also study the application of machine-language for

sound production in practical examples. Typical of this non-

standard approach is that a student or composer has hardly any

possibility of describing concrete musical quantities such as

pitches, timbres or loudnesses and arranging them in time.

Instead he must try to describe and order elements of musical

language such as short, long, uniform, varied, contrast, silence,

similar, dissimilar, transition and the like, these terms

referring to the microstructure of the sound and to the macro-

structure of the form.

The Sound Synthesis Program (SSP) I designed in 1972 proceeds

from comparable viewpoints. In this non-standard approach samples

are not generated by random or arithmetical/logical machine

operations, but collected in sound segments which in their turn

are taken from separate amplitude and time lists. The selection

of amplitude and time values is made according to principles

originating in PR2. The number-pairs in a segment designate

turning-points of the oscillation curve which are interpolated

linearly in real time during sound production. The number of

segments which a composer can define is limited only by the

capacity of the core memory; the order of segments is free within

the framework of the same selection principles according to which

the segments were produced. At the Institute we are considering

the development of a special digitally-controlled generator which

will call the sound segments from disk files, thus doing away

with the limitations of the core memory. It would then be possible

to realize the concept on which SSP is based: to describe the

composition as one single sound, the perception of which is re-

presented as a function of amplitude distribution in time as

sound and silence, soft and loud, high and low, rough and smooth.

Program-generating systems

I can be brief on the subject of program-generating systems,

because their development is in full swing at present, and there

are no tangible results as yet. Still, investigation into com-

posing programs and sound programs have consequences which are

beyond the scope of the individual composition or construction

of sounds. Although composing programs do contain fundamental

statements about musical language systems, as well as personal

strategies, they have neither been systematized, nor do such

composing programs permit systematic research. It looks as though

a super-individual approach must be found.

Steve Holtzman, of the Artificial Intelligence Department at the

University of Edinburgh has been looking into this problem

recently, and has described his work at Edinburgh and Utrecht in

various articles.  I shall close my paper by quoting a few pas-

sages from these articles.

"The basic proposition is that music be considered as a hier-

archical system which is characterised by dynamic behaviour.

A `system' can be defined as a collection of connected objects...

The relation between objects which are themselves inter-

connections of other objects define hierarchical systems...

It should be made clear that in talking of the meaning of music

or language, it is not necessary to have a referent for each

sign... Meaning is a question of `positional' value. One is not

concerned with the `idea' or referent as objects but rather

'with values which issue from a system'. The values correspond

to cultural units but they can be defined as pure differences...

`Units of meaning' are not defined referentially but structurally -

diacritically. We can look at a structure that consists of (dia-

critically) defined units in a complex of transformations and

relations. Meaning becomes not `what units say/refer to/etc.'
but `what they do' - a question of function in a structure."

"In recent research, we have been developing a machine which itself,

i.e. automatically, can generate program text to synthesize

distinctive sounds and control-programs to manipulate smaller

chunks of program. The machine approaches sound synthesis in the

so-called non-standard manner...

 The program generator at present occupies 5K core, with remaining

free core (i.e. 20K) available for object text.  It is implemented

on a PDP-15 and requires a dedicated system-. Special hardware

used is some digital-to-analog converters with 500 nano-second

response time, a hardware random number generator and a hardware

arithmetic unit.

 The prdgram works in a `bottom-up' fashion first writing small

chunks of text (in compiled machine-code) that create distinctive

sounds, then writing control-functions to manipulate these

sound-producing programs to create `phrases' of juxtaposed sounds,

again, control-programs for the subordinated phrase-programs to

generate larger structures, and so on. The synthesis system is

hierarchical and consists of a number of distinct levels, each

in turn subordinated to another...

Over all the rules presides what we call the complexity factor.

The relations between the parameter values must interact in a

manner which is within the bounds of an evaluation of their

complexity measure....  The complexity evaluation, for example,

considers the number of samples that compose the sound, the

larger the number of samples the more complex the wave is said

to be, and similarly, the more operators used or the more

variables, the greater will be the complexity; At present (...)

we are trying to develop an algorithm which might be said to

embody an understanding of these relationships and which could

be used as the basis for a grammar to generate a grammar (which

in turn generates a sound producing function)

                                                      June 1978


1)   Buxton, W., "A Composer's Introduction to Computer Music",

     Interface 6,2, Amsterdam and Lisse, 1977.

2)   a) Hiller, L., Isaacson, L., "Musical Composition with a

       High-Speed Digital Computer", J.A.E.S. 6,3 (1958).

     b) Hiller, L., Isaacson, L., Experimental Music, New York,
       McGraw-Hill, 1959.

     c) Hiller, L., "Computer Music", Scientific American 201,6,


     d) Xenakis, I., Formalized Music, Bloomington, Indiana

       University Press, 1971.

     e) Koenig, G.M., "Project 1", Electronic Music Reports 2,

       Utrecht, Institute of Sonology (1970).

     f) Koenig, G.M., "Project 2 - A Programme for Musical Com-

       position", Electronic Music Reports 3, Utrecht, Institute

       of Sonology (1970).

3)   a) Smith, L., "SCORE - A Musician's Approach to Computer Music",

       J.A.E.S. 20,1 (1972).

     b) Tanner, P., "MUSICOMP, an Experimental Aid for the Composition

       and Production of Music", ERB-869, Ottawa, N.R.C. Radio and

       Electrical Engineering Division, 1972.

     c) Mathews, M., Moore, F., "GROOVE - A Program to Compose,

       Store, and Edit Functions of Time", Comm. ACM 13 (Dec. 1970).

     d) Truax, B., "The Computer Composition - Sound Synthesis

       Programs POD4, POD5, & POD6", Sonological Reports 2,

       Utrecht, Institute of Sonology (1973).

     e) Buxton, W., Manual for the POD Programs, Utrecht, Institute

       of Sonology, 1977.

4)   see remark 2e

5)   see remark 2f

6)   Holtzman, S.R., A Description of an Automated Digital Sound

     Synthesis Instrument, unpublished manuscript, April 1978.

7)   a) Mathews, M., The Technology of Computer Music, Cambridge,

       M.I.T. Press, 1969.

     b) Vercoe, B., "The MUSIC 360 Language for Sound Synthesis",

       American Society of University Composers Proceedings 6 (1971).

     C) Vercoe, B., Reference Manual for the ~!USIC 360 Language for

       Digital Sound Synthesis, Cambridge, unpublished manuscript,

       Studio for Experimental Music, M.I.T., 1975.

8)  Chowning, J.M., "The Synthesis of Complex Audio Spectra by

    Means of Frequency Modulation", J.A.E.S. 21,7 (1973).

9)  see remark 3d

10) Kaegi, W., Tempelaars, S., "VOSIM - A New Sound Synthesis

    System", J.A.E.S. 26,6 (1978).

11) see remark 6

12) a) Berg, P., PILE2 - A Description of the Language, Utrecht,

       unpublished manuscript, Institute of Sonology, January 1978.

    b) Berg, P., A User's Manual for SSP, Utrecht, unpublished

       manuscript, Institute of Sonology, May 1978.

13) Holtzman, S.R., Music as System, DAI Working Paper 26,

    Department of Artificial Intelligence, University of Edin-

    burgh, April 1978.

14) see remark 6

Original republished in Gottfried Michael Koening, Aesthetische Praxis /
Texte zur Musik, Band 3, 1968-1991, PFAU Verlag, 1993, pp. 191-210, 
as "Kompositionsprozesse"

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