MP1
a computer-assisted composition program
MP1, written by Sever Tipei, was first used in 1973.
Although its underlying structure remained the same over the years,
MP1 has been evolving continuously, a frame-work in progress
to which new features are added. Based on the proposition
that the sounds of a composition can be described as entities in a
multidimenssional vector space, the program has three
interlocked layers: stochastic distributions,
sieves or logical filters, and Markov chains.
Any number of two or more sound parameters (sound
characteristics) can be defined for an arbitrary number of
parts (streams of events); by default, the first parameter
is assumed to be time. For each parameter, equivalence relations
mod m of the form:
are described
where n is the equivalence class and m is the size
of the equivalence class. This way, control over details is
exerted through n while the broader aspects (such as octave
or register in the case of pitch) are controlled through k.
The main loop of the program assigns values for each sound parameter
by matching the probability of various elements on a list of
possibilities with a random number. A choice is
completed when all such values are assigned for an event.
MP1 is a comprehensive program in the
sense that once the computations start, the user can not intervene
until the piece is finished and then, either accepts or rejects the
result. This way, the composition is treated as a process which,
once triggered, is capable of continuing on its own, like a natural
phenomenon. In the author's mind, this approach
- elevates the act of composing with computers to a higher or
meta-level,
- insures its integrity of the process, and
- uses the computer as a collaborator in stead of a dumb slave.
Stochastic layer:
A list of possibilities is created starting with preferred
(mean) values for both n and k and their deviations
(variances) which are defined by the user. The
range of the instrument or sound source for that particular
parameter is also taken into account along with preferred
intervals between adjacent values and their deviations.
Next, coherence factors between successive values and/or
intervals both at the same part and between simultaneous parts are
considered. Eventually, each element on the list is assigned a probability
(along a normal-like distribution curve) by comparing it with the
preferences specified by the user.
Sieves:
Logical expressions containing modulo m terms,
sieves are used to extract subsets from a continuum. An
example in the pitch domain would be the selection of a certain
scale out of the total chromatic. Besides simply retaining or
discarding elements, sieves can, at the same time,
assign weights to the elements allowed to pass through. A
powerful tool, sieves are also used in MP1 to correlate
various sound parameters and establish an equivalent to
orchestration constraints: values at one parameter which may not
coexist with certain values at another one are rejected. For
example, a ten second, very soft sound can not occur in the high
register of the piano.
Markov chains:
MP1 can handle patterns or strings of elements
defined at one or more parameters. They are treated as Markov
chains and they refer to intervals between consecutive
values (e.g. durations, not absolute timings; pitch intervals,
not absolute pitches).
Sequences of arbitrary length can be constructed if, in stead of
considering the probability of an interval following another, the
probability of an interval to follow a certain number of others which
have already occurred in a certain order is considered.
When such patterns are defined simultaneously for
most or all parameters, motives or themes
in the traditional sense could result.
The 100% option:
In MP1 the user has the possibility to specify the accuracy
with which patterns are reproduced. When 100%
accuracy is desired, all other options are short-circuited and the
pattern is copied without change. However, this
operation might not be possible due to range
restrictions and/or to the sieves in effect at that
moment. In order to avoid such situations, MP1 finds out
before starting to copy the pattern if its exact
reproduction is possible. All transpositions of the
pattern are tried and if none of them is successful,
the option is abandoned.
Chords:
Vertical aggregates can be created in MP1 in two ways:
- by having an arbitrary number of parts
contribute one sound each, similar to a contrapuntal
texture where chords are the sum of simultaneous
independent lines;
- by declaring them as one of the sound parameters
, giving values to various chord-sizes, and
choosing particular chords form a library.
The second option was used in Aga Matter, for
piano and tape (see reference below).
Entering data:
All information contributing to a choice is controlled
by the user and it can vary during the piece.
This results in large quantities of data if care for detail is
desired. Two auxiliary programs, PREAUX and AUXIL
allow the user to enter and/or edit the data used by MP1.
Pieces produced with MP1:
- Rice Matters, computer generated
tape, 1993.
- Aga Matter, for piano and computer
generated tape, 1992.
- Many Worlds, for percussion ensemble,
1989.
- Cuniculi, for five tubas, 1986.
- Maiden Voyages-II, for trumpet, piano,
three slide projectors, and two channel tape, 1985.
- Maiden Voyages (first version), 1984.
- Clariphannies, for solo clarinet, 1980.
- Undulating Michigamme, for soloists
and orchestra, partially generated with MP1, 1977/78.
- Portrait Of The Artist As A Young Woman Killing
Herself With A coup de telephone,
In MI 48105, for four female voices, 1975.
- Les Liaisons Dangereuses, for five
amateurs, 1974.
References:
- MP1 Revisited: AGA MATTER for Piano
and Computer Generated Tape, Proc. 1994 Int'l
Computer Music Conference (Aarhus, Denmark; September
1994), International Computer Music Association, San Francisco,
CA, 1994, pp. 3-6.
- The Computer, a Composer's Collaborator,
LEONARDO Journal of the International Society for the Arts,
Sciences, and Technology, vol.22, no. 2, 1989, pp. 189-195.
- (Super)Computer Produced Musical Manifolds,
Contemporary Music Forum; Proc. Bowling
Green State University New Music and Art Festival 10 Paper
Sessions, Vol.1, (Mid-American Center for Contemporary
Music, College of Musical Arts, Bowling Green State Univ.,
Bowling Green, Ohio; 1989), pp. 23-26.
- Manifold Compositions - a
(Super)computer-assisted Composition Experiment in Progress
, Proc. 1989 Int'l Computer Music Conference
, (Ohio State Univ., Columbus, Ohio; November 1989),
International Computer Music Association, San Francisco, CA,
1989, pp. 324-327.
- MAIDEN VOYAGES - a Score Produced with MP1,
Computer Music Journal, vol. 11, no. 2, M.I.T. Press
Journals, Cambridge, MA., 1987.
- MAIDEN VOYAGES - a Score Produced with MP1,
Proc. 1985 Int'l Computer Music Conference,
(Vancouver, B.C., Canada; August, 1985),
International Computer Music Association, San Francisco, CA,
1989, pp. 259-265.
- Solving Specific Compositional Problems with MP1
, Proc. 1981 International Computer Music
Conference, (North Texas State Univ., Denton,
Texas; November 1981), International Computer Music
Association, San Francisco, CA, 1989, pp. 101-109.
- MP1, a Computer Program for Music Composition
, Proc. Second Annual Music Computation
Conference, (Univ. of Illinois, Urbana, Illinois,
November 1975), pp. 68-82
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