andre atta micro tonality

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  • Microtonal CompositionAlain Bancquart, Carlos Agon and Moreno Andreatta

    This chapter deals with certain theoretical and programming aspects of microtonal com-puter-aided composition. After a brief introduction on the problem of microtonality,Carlos Agon will describe a few computer tools developed in OMicron, an integratedOpenMusic extension dealing with the musical notation of microtonal systems. Thestudy of microtonality raises very interesting theoretical issues, particularly those whichconcern combinatorial problems. Moreno Andreatta will discuss these issues taking as apoint of departure a description of the algebraic method, also implemented in OpenMusic(MathTools package). In the third part Alain Bancquart will discuss certain aspects ofmicrotonal composition used in his piece Amour grand terrible champ critique and somecorresponding models represented with the theoretical and computational tools describedin the previous sections.

    Historical introduction

    The division of the octave into twelve equal semitones and the hierarchical tonal orga-nization of intervals are relatively recent phenomena which date from the end of theseventeenth century. Before that time, according to physical rules, the semitones wereunequal and as a consequence modulations were not feasible in all keys. The great vari-ability of the constitutive element of the sound space led sixteenth-century musicians andscholars to propose new divisions of the octave. For instance, the music-theorist NicolaVicentino (1511-1576) invented two instruments, the Archicembalo and the Archiorganowith thirty-one keys for one octave. Vicentino wrote a few four-part and five-part madri-gals where he used quarter-tone accidentals on certain notes of the chord and mostfrequently on the thirds. The result was neutral harmonies which sound neither majornor minor and which lend a surprising expressionist flavour to this modal music. Theidea that the sound universe is not necessarily divided into twelve is therefore not new. Itderives from the proclivity for rational practice that took over in the eighteenth centuryat a time when people were eager to establish stable scientific and intellectual laws.

    Every system, however perfect, is one day corroded to the point when it becomesobsolete. That is what happened to the tonal system at the turn of the twentieth cen-tury. In fact, the amelioration of the tonal system brought about by the increasinggeneralisation of chromaticism eroded its very foundations. Concurrently, the rhythmwhich derived from tonal harmony and which gave the tonal organisation its remarkablestability evolved around the same lines. Irrational values appeared notably in Scriabinsworks (1871-1915), combined with an emancipation from the tonal system with the use

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    of modes (and particularly of mode 2, dear to Olivier Messiaen) and chords composed ofsuperimposed fourths that he called synthetic chords.

    Thus, twentieth-century musicians were faced with the necessity to rebuild a sounduniverse deprived of its organisation and, in a certain way, of its meaning. Two pathswere taken. On the one hand some promoted the equality of the twelve tones in a musicwhich is no more based on hierarchical principles. This led Schoenberg (1874-1951) todevise the twelve-tone series that paved the way to what we call the serial technique.On the other hand, three composers developed a more radical approach: Alois Haba(1893-1973), Juan Carrillo (1875-1965), and Ivan Wyschnegradsky (1893-1979).

    Alois Haba is a Czech composer who wrote two theoretical works: The HarmonicFoundations of the Quarter-Tone System (1922) andNeue harmonielehre (1927), in whichhe proposes a new theory for ultra-chromatic composition. Despite the interest that suchnovelty may have raised, Habas music is in fact close to Dvoraks style and not reallyinnovative.

    Juan Carrillo is a Mexican composer of Indian descent who first trained as a violinist.His practical experience certainly motivated his interest and systematic research aboutmicrotonal intervals. As early as 1927 he devised the construction plans for fifteen pianosusing intervals from the third tone to the sixteenth tone. These instruments were built in1958 and are now on display at the Carrillo Foundation in Mexico City. Although he wasan ingenious inventor, Carrillo was not really a convincing composer. It is noteworthythat he acknowledged Claude Debussys influence, in a way foreshadowing the works byMaurice Ohana in third tones, works which are also deeply indebted to Debussy.

    Wyschnegradsky was a Russian composer born in Saint Petersburg. His early workswere influenced by Wagner and, above all, by Scriabin. He also borrowed from the latterthe idea that music is redemptive and possessesa theurgical force of an incommensurablepower that will transform mankind and the whole cosmos (Marina Scriabin). Through-out his whole life Wyschnegradskys thought was driven by this mystical conception.Micro-intervals were instrumental in his attempts to get closer to sound continuum.1 Heexplored all the possible densities, reaching the density of 96 which corresponds to thesixteenth tone. His exploration ventured beyond the realm of pitches: he understoodthat the relation between space and time was crucial. His theoretical work is important,be it only because it mentions the idea of rhythmic micro-intervals. Wyschnegradskyproposed to rearrange the sound space into what he called non-octaviant spaces, whichcorrespond to micro-intervallic scales organised as cycles and which exceed or do notmeet the octave.

    Wyschnegradskys extensive musical works contain very beautiful passages, such asthe pieces for two or more pianos tuned with a quarter-tone dierence (see notablyCosmos for four pianos, Study on rotating motions for two pianos, Integrations for twopianos), three string quartets and his last opus, a string trio.

    In addition to these three pioneers, we must also mention Pierre Boulezs cantataon a poem by Rene Char, Le Visage nuptial. The first version of this work is for smallorchestra and was composed between 1946 and 1947. The second version, for soprano,contralto, female choir and big orchestra, was composed between 1951 and 1952. Threeout of the five movements in this version are in quarter tones. Due to the fact that thiswork is extremely dicult to perform, Boulez composed a third version between 1985 and

    1See his major theoretical work, La loi de la pansonorite, published seventeen years after his death [8].

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    1989, in which he got rid of the quarter tones. Despite the interpretative diculties, thesecond version represents the most accomplished microtonal composition during whatcan be termed the exploratory period of new scales. Boulezs use of quarter-tone seriesmay explain the performance problems linked to this piece, but it represents a bridgebetween the two practices that came after the end of tonality: the serial technique onthe on hand and the microtonal technique on the other.

    Micro-intervals in OpenMusic: OMicron

    Carlos Agon

    OMicron is the fruit of a collaboration between composers, musicologists and computer-scientists. It is an OpenMusic extension designed for the representation, the manipula-tion, the notation and the rendering of microtonal structures.

    In OpenMusic pitch representation is closely linked to the MIDI standard. It is usefulto recall that in this system pitches are expressed by whole numbers (e.g. C3 = 60, D3= 62, etc.) A MIDI pitch unit is equal to a semitone. The midicent (that is, C3=6000,D3=6200, etc.) is taken as the unit in OpenMusic to accommodate microtonality (asemitone equals 100 midicents). According to this convention a quarter tone is equal to50 midicents, an eighth tone to 25 midicents, and more generally a 1/n interval to 200/nmidicents. Several tools were developed in OpenMusic to allow working with midicents.Conversion tools (see Figure 1) were particularly important.

    Figure 1. Conversion tools for midicents in OpenMusic. The function approx-m produces anapproximation in midicents to the closest tempered division of the octave ; with mc->f themidicents are converted into frequencies (Hz) and with f->mc it is the opposite; with n->mca note symbolically described by a letter and a number is converted into midicents, and withmc->n it is the opposite (quarter tones are expressed by -, and third tones by +; the sub-divisions smaller than a quarter tone are expressed as a dierence between the closest quartertone, e.g. midicent 8176 corresponds to Bb4-24).

    There exist other more general functions for the structuring and modification of midi-cents (for instance om+ for transposition, and so on).

    Notation of the microtonal intervals

    Since we are trying here to notate equal divisions of the whole tone, the problem of micro-intervallic notation can be reduced to finding symbols for the accidentals representing thevarious intervals within a tone. This section describes the accidentals used in OpenMusic.

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    Of course, this account remains an open proposal that needs to be improved in practice.The development of such accidentals was motivated by three factors: respect of andadaptation to existing notational systems (at least for the quarter tones and the eighthtones), readability (the signs should not take too much space in the score), and a certainlogic by which the signs give information about the notated interval.

    Figure 2 shows the accidentals corresponding to quarter tones. Note that flats areexcluded from this notational system: the symbolic logic here is exclusively incremental.

    Figure 2. Notation for the subdivision into quarter tones.

    The notation for th