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Page 00000001 REPORT OF THE COMDASUAR: A SIGNIFICANT AND UNKNOWN CHILEAN CONTRIBUTION IN THE HISTORY OF COMPUTER MUSIC Martin Alejandro Fumarola LEIM, National University of C6rdoba Estafeta 56 RA-5001 C6rdoba ARGENTINA maralefo @hotmail.com ABSTRACT This paper describes the Intel 8080 microprocessor-based musical instrument called COMDASUAR (it stands for COmputador Musical Digital Analogico Asuar), which was devised and developed in 1978 by the Chilean engineer and composer Jose Vicente Asuar, one of the pioneers of electroacoustic music in Latinamerica. Both the hardware and software (with 26 subprograms) components are further explained pointing out the computer-related compositional possibilities. This paper embosses COMDASUAR's uniqueness and pioneer role in the world history of computer music since it does not register any equivalent at the end of the seventies and serves for the revalorization of Latinamerica in the world context of electroacoustic and computer music. I. INTRODUCTION Chilean engineer and composer Jose Vicente Asuar is, along with Juan Amenibar, one of the pioneers of electroacoustic and computer music practise in Chile and in the whole Latinamerica region [Fumarola, 1998]. In 1958 he founded the "Estudio de Mtisica Electronica", the cronologically second one in Chile and in Latinamerica. His electroacoustic piece "Variaciones Espectrales" is one of the pioneer works in Latinamerica together with Juan Amenibar's "Los Peces". Jose Asuar was extremely aware of the computer music experiences that had been carried out in the USA, Canada and Europe from 1955 onwards, as he summarizes in his Paper "Un sistema para hacer musica con un Microcomputador" [Asuar, 1980]. A sharp knowledge of the early and posterior achievements of Lejaren Hiller, Leonard Isaacson, lannis Xenakis, and Max Mathews, among others, is undoubtedly present in the way he entered upon the COMDASUAR, and not only it; his background in the musical applications of computing science and programming is clearly noticeable in several of his previous pieces (both instrumental and electroacoustic), and in his articles published in the "Revista Musical Chilena". His historical awareness is untypical in Latinamerica since most practitioners of electroacoustic music in Latinamerica in the time tended to work isolated with respect to their colleagues in North America and Europe. If we are going to apply the distinction between 'electroacoustioc music' and 'computer music', it is very wise to state that whereas Juan Amenibar is the pioneer of electroacoustic music in Latinamerica, Jose Asuar is the pioneer of computer music in that subcontinent. His formation as engineer helped him out, evidently. The COMDASUAR puts into evidence, among other things, Asuar's deep understanding of the electronic side of computers' architecture. Besides, the differenciation between supercomputing and microcomputers is mentioned in his articles, something that no other composer did in Latinamerica at that time. On the other hand, his musical training was very profondous, making easy for him to develop a very particular compositional thought, in which his influence from the serialism as well as from the stochastic approach are distinctive qualities. The COMDASUAR is the first computer music instrument in Latinamerica, bringing computing sciences applications and music together.
Page 00000002 II. PREVIOUS REALIZATIONS Before to the design and implementation of the COMDASUAR, Jose Asuar had several important accomplishements in electroacoustic and computer music, including meaningful instrumental pieces devised by computer music methodologies. Above all, the most important is "Formas I" (1970) produced in collaboration with the "Grupo de Investigaciones en Tecnologia del Sonido" [Asuar, 1972]. That work makes application of probabilistic processes to composition, algorithms based on serialism but with probability, "directed probability", histograms, sequences, and it is programmed in FORTRAN IV. Two vinil disks with Asuar's pieces had been released before to the birth of the COMDASUAR: "El Computador Virtuoso", and "Mtsica Electr6nica de Jose Vicente Asuar". III. GENERAL DESCRIPTION OF THE COMDASUAR The COMDASUAR is able to perform any musical score in an authomatic manner (i.e., with no human intervention), having a poliphonic capacity of up to 6 voices. It is completely tuned and sincronized, with the feasibility to choose the timbre for each voice. Its most outstanding compositional features include, for example: the possibility to develop heuristic programs, and to propose musical ideas based on probability and musical gambles. The COMDASUAR was the first musical instrument based on a microcomputer developed in Latinamerica. Some of its general characteristics are the following: -unexpensive: the total cost of its components was around U$ 1,000 in 1978. -broad range of use: from a home use replacing a piano until a concert performance including its use as a tool for a composer. -sounds produced in real time. It is possible to modify the musical results while they are listened to. Its frequency range is equivalent to the audible range (8 octaves). -poliphony of up to 6 voices -standard QWERTY keyboard for data entry as well as a TV-like monitor -sounds obtained from the microcomputer are square waves, which are passed on to analogical units which transform them in the resulting timbres. It gives a balanced and equalized mixing result of the 6 voices that must be able for performance or recording. -it can perform any musical score, offering heuristic possibilities. IV. EXPLANATION OF THE SOFTWARE it is written in machine language and ocupies 5 Kbytes of memory. It has 26 subprograms, each one named with the letters of the alphabet from A to Z. Those subprograms are divided into: Al Commands for the computer: 1)displays in the screen the content of the memory, 2)erases the screen (2 pages), 3)stores information in memory, 4)changes data in memory, 5)moves memory allocation, and 6)executes programs (2 subprograms). A2 Operations with musical data: 1)introduces data (3 subprograms), 2)changes data, 3)removes data, 4)interpolates data, 5)moves pitches, and 6)moves durations. A3 Heuristic: 1)Canon, 2) Retrogradation, 3)transmutes tones, 4)transmutes durations, 5)probability, and 6)inserts groups of durations. A4 Convertion to sound: 1)with sincronism (2 subprograms), and 2)without sincronism. A5 Control of periphericals: 1)it records cassettes, and 2)plays cassettes. All those programs of A are recorded in the EPROM so it is possible to resort them at any moment. In addition, other programs were developed, specially heuristic ones, which are stored in cassette and can be utilized from a certain location of RAM memory. In those cases, it is necessary to trespass the desired program from the cassette to the foreseen memory location. In fact, this allows to extend the memory capacity to an undefinied quantity of programs. B Musical Codes, each one expressed by its pitch and duration: Bl. Pitch, expressed in 3 ways: Octaves: a number from 0 to 7, which implies 8 octaves Grade in the scale: with letters according to the standards of American format: A, B, D, E, F, and G. R for the silence Cromatism: the standard, S, W, and Q
Page 00000003 Quarter tones alterations: U = ascending quarter tone, T = three ascending quarter tones, V = descending quarter tone R = three descending quarter tones B2 Duration It is expressed according to the terminology in Spanish: R = redonda, B = blanca, C = corchea, N = negra, S = semicorchea, F =fusa, M = semifusa, L = lunga, P = punto (it multiplies the previous value by 1.5). Any duration value can be obtained by the addition of the aforementioned values. Besides, the following ciphers are defined: 0 = normal, 3 = triplet, and so on for the irregular values. B3 Final Denomination For the reading on the screen, the computer numbers automatically each tone. As soon as it is finished to write the pitch or duration of a tone, the composer presses the space bar, what is represented in the screen with the symbol I. Example of a score written for the COMDASUAR: 0001 5BWI ONFI 0004 6E1/ Cl 0002 3BQI 3C1 0005 2DU/ 7B1 0003 R/ OS! B4 Redundancy In order to simplify and speed up data introduction, the COM~DASUAR takes advantage of the enormous redundancy of musical data. In this sense, only it is indicated to the computer those elements that change from tone to tone. Any element of notation like an octave, grade, cromatism, duration that keeps constant, it is not necessary to mention it, the computer assigns the value it had in the previous tone. Example: 0001 3C1 Cl 0004 I I 0007 El/ NI 0002 I I 0005 GI I 0003 E/ I 0006 I I The COMDASUAR also takes advantage of redundancy by defining different modes of introducing musical data: Mode 0 (JO): it is the usual mode, as seen in the previous examples. For each tone, its pitch and duration are indicated. Mode 1 (Ji): Constant duration. At the beginning, the value of the common duration to a tones series is indicated. After that, only the pitch of each tone is indicated: Ji 38 0003 B 0006 4A 0009 D 0001 3C 0004 F 0007 B 0010 E/ OB/ 0002 D 0005 G 0008 C JO Mode 2 (J2): Constant pitch. At the beginning, the value of the conmon pitch to a rhytmical sequence is indicated. After that, only the duration of each tone is indicated: J2 4C 0004 N5 0008 JO OOO1 CP 00058S 00090OC 0012 3G/ OB/ 0002 0006 3 0010 5/ 0003 5 0007 0011 7/ Mode 4 (J4): Reiteration. This mode is utilized when a tones succession is repeated at least once. First, it is indicated the number of times it repeats, and then, the tones succession, which is limited by another mode indicator. This mode is specially useful for representing trills, tremoli, etc. Mode 5 (J,5): Repeats a sequence. This mode inserts a sequence that has already been written before. There is no limitation in the extension of the sequence to be repeated. Both the first and the last tone of the sequence to repeat are indicated: 0001 3C/ N/ 0004 4C/ JO 0010 4C/ R/ Ji C! 0005 B/ 0008 C/ B/
Page 00000004 0002 El 0006 A/ 0009 3G1 I 0003 GI 0007 B! J5 1/ 7! B,5 Texture. Asuar defines the texture of a sound to "its variation like a glissando or a vibrato. GlissaLndo. It is expressed like Mode 3 (J3) and defined indicating the pitches of the beginning and of the end of the glissando and its duration. The glissando is obtained as a fast succession of tones whose difference of frequency is very little and follows the direction of the glissaLndo. The computer calculates the number of tones it must output and the frequency of each one, based on a fixed speed for the succession of tones that is the l6" part of a semifuse. By employing this procedure it is possible to obtain any design of frequency variation: Vibrato. It is calculated by points of a sinusoide whose axis is the central tone and its amplitude the 16th part of a tone. The frequence of repetition depends on the position of the Tempo regulator. For a Tempo N = 60, it is of 8 cicles per second. The computer calculates 32 points of this sinusoide according to a table. Due to the speed those sounds are issued, it happens something similar to the glissandi and a continuous vibrato is heard. The beginning of a vibrato is indicated as Mode 6 (J6) and its end as Mode 7 (J7). Between those 2 indications, any quantity of tones can be placed: C Heuristical Programs. For Jos6 Asuar, heuristical programs are those ones in which the computer has a creative intervention (it issues a score in the memory) or acts as a performer (it manipulates a score stored in memory). The following programs are stored in the EPROM of the COIMDASUAR: Cl. Canon C2. Retrogradation. It is necessary to indicate the initial and the ending tones of the section that is retrograded. C3. Tones Transmutation. It can be run with at least two voices in memory. It allows to exchange the pitches of the tones corresponding to the 2 voices while the durations remain unchanged. It is mandatory to indicate from which tone in each voice the transmutation is realized. C4. Durations Transmutation. SimilaLr to the previous one. It exchanges durations while keeping the pitches. Jos6 Asuar states that he developed these 2 programs influenced by his former Professor Boris Blacher. At this point, we have a wide spectrum of possibilities for composing music. C5. Probability. For this program it is necessary to define and quantify the musical elements that will be affected by probability. The COMDASUAR allows the simultaneous and independent probabilistic organization of registers, pitches, durations, harmony, and sound texture (vibrato and glissando). C6 Insertion of group of durations. Normally, the tones lists sprouted by probaLbilistic programs are monotonous and unarticulated. With this program is possible to interpolate pauses and to make possible that tones groups of the probabilistic series have the same duration. The quantity of tones, its location and the constant duration are also calculated by probabilities. C7 Another heuristical programs. Jos6 Asuar developed several additional heuristical programs for meeting the requirements of specific musical fra;gments. One of the best examples is the piece 'Asi habl6 ci Computador", appearing in the LP of the same name, which was composed based on a numerical series and in various arithmetical gambles that determine the rhythm of some of its voices. In other compositions, Jos6 Asuar utilized aleatoric combination of groups of durations with groups of pitches. Of special interest are the weird mixtures, such as, of modal series with rhythmical series belonging to the serialism as well as using the melodies of the Argentinian vidalita, as in pieces of the LP "Asi habl6 el Computador". Several procedures of the serialism were utilized. V. HARDWVARE D Tones obtainment All tones are attained from an only quartz oscillator. This oscillator resounds at the frequency of 2,048 kilocicles and the different tones are obtained by divisions or subarmonics of this generating frequency. Let's take the example of an oscillator that resounds at 28,160 cicles per second: it is outside of the audible spectra but if it is divided by 64 (the subaimonic of order 64), we obtain a pitch of 440 c.p.s. (A). Between 64 and 128 we have 64 possibilities of division
Page 00000005 or subarmonics, and if we choose all those that are nearer of the values of the tempered scale, we can obtain a musical scale of aproximate tuning. Therefore, the worse tuning, which corresponds to the high pitches, has a definition in the subarmonic 70, which is equivalent to a quarter tone, aproximately. The lower the pitch the better the tuning. Tones are get by a system of division of frequencies supplied by the INTEL Timer 8253. This Timer is capable of obtaining simultaneously 3 different subarmonics from the same generating frequency. With that purpose, the microprocessor delivers the dividing cipher, with a definition of 16 bits, to each one of the 3 dividers of the Timer, attaining the 3 tones as subarmonics of the same oscillator, having stable intervalic relations. In the COMDASUAR, it is possible to work either with a quartz oscillator that delivers a fixed frequency of 2,048 kilocicles or with an oscillator of variable frequency, which can be used manually or with voltage control. Therefore, there are two possibilities for obtaining the tones: by fixed tuning and by variable tuning. E. Rhythm Obtainment For producing rhythm, the COMDASUAR makes use of a quality of the microprocessors: the possibility to be activated by interruptions of the external media. The inner logics of the COMDASUAR has a program for interruptions waiting. When an interruption comes, the microprocessor goes to execute the main program, which consists in decrementing the counters in charge of counting the duration of each tone. As soon as the counters are decremented, the microprocessor goes again to the program of interruptions waiting in order to repeat the process. The COMDASUAR employs a multivibrator of variable frequency for generating the interruption pulses which allows to manually obtain accelerandi and retardandi. The maximal spped is around the 19 or 20 tones per second and per voice. F. Analogic equipment For each voice, one filter with voltage control, one envelope generator, and one amplifier with voltage control are built. The control voltages for the filters are obtained from six digital-analogic converters connected to 7 bits of each port of two paralel interfaces (Programmable Peripheral Interface, INTEL 8255). The 8th. bit is used as trigger for launching the envelope generator. Three of the voices have at their disposal a wave form generator, which consists in a demultiplexor that divides the square wave in a wave of 8 segments. The original frequency is divided in eight parts as well, i.e., the pitch of the tone decreases in 3 octaves. By passing this stepped wave through the filter, it is possible to attain different spectrums, in which it is possible to gamble with the relative magnitudes of the first 8 armonics. With this procedure it is possible to achieve a very convincing synthesis of many well-known timbres, such as of some acoustic instruments. The COMDASUAR also includes additional analogic equipment for the generation of effects: a white noise generator, a rose noise generator, two ring modulators used for getting inarmonic espectra like bell sounds, two tremolo generators, two generators of functions oscillating at low frequency with the goal of generating sinusoidal, triangle, and square voltages, which control filters and amplifiers for attaining different effects (vibrato, tremolo, etc.). A dephaser for accomplishing spatial-like effects as well as complementary units like inverters, multipliers, mixers, reverberators, etc. are also available in the COMDASUAR. G. Scores storage. The RAM memory where musical data are stored has a size of 2 Kbytes. Because of the simplicity of many codes and to the information reduction by redundancy, this memory size allows to store up to 2,000 tones in the 6 voices. This information is physically placed within a cassette. The transference of music data from the cassette to the memory of the COMDASUAR is very fast, it takes only a few seconds.
Page 00000006 H. Synchronism. As it was stated before, the poliphonic capacity of the COMDASUAR is up to 6 voices. For producing performances of more than 6 voices, it allows to syncronize them by resorting multi-track equipment. In the case of a 4 track recorder, one track is appointed to record a pulse for originating the interruptions. In the remaining 3 tracks, up to 18 voices (up to 6 in each individual track) can be recorded with total sincronism. For the recording of the pieces featured in the LP "Asi habl6 el Computador", a 2 tracks REVOX A77 tape recorder was utilized. The sincronism in the 2 tracks was obtained by recording a reference tone at the very beginning of track holding the first recording. After the issuance of that tone, the COMDASUAR counts certain amount of time and starts to perform the score. For syncronizing the second recording, it is necessary to play the track with the reference tone, and after this last one, the computer begins to play the new score. CONCLUSION The COMDASUAR has been useful not only for high-end computer-based composition but also for pedagogical and teaching purposes. Many of its features were an advance of computer music developments that came years later. Jose Asuar then suggested several new additions and improvements that made the COMDASUAR an authentical tool for composing and real-time performing music, for instance, the inclussion of piano-like keyboards, firstly one monophonic, then two monophonic, and finally one polyphonic. Sensors and optoelectronic devices have also been tried and this could have the most important potential field for its development. The COMDASUAR is a pride for Latinamerica and has to be included in all the manuals and handbook listing and describing pioneer computer music instruments. The uniqueness of the COMDASUAR as a sequencer, a score editor, an algorithmic composition tool, and a sound synthesis program puts it in the same seat of honor as the key computer music developments of the USA and Europe. REFERENCES [Fumarola, 1998] Martin Fumarola. "Interview with Juan Amenibar - More than 40 years of electroacoustic music in Latinamerica", to be published in Computer Music Journal 22 (3). [Asuar, 1972] Jose Vicente Asuar. "Miisica con Computadores: Como hacerlo?", Revista Musical Chilena N~ 118, Pages 36-66, April-June 1972 [Asuar, 1980] Jose Vicente Asuar. "Un sistema para hacer musica con un Microcomputador", Revista Musical Chilena No 151, pages 5-28, July September 1980.