Page  114 ï~~PAT-PROC An Interactive, Pattern-Process, Algorithmic Composition Program Phil Winsor Center for Experimental Music and Intermedia University of North Texas Denton, Texas 76203 (FA12@UNTVAX.BITNET) and Computer Music Studio National Chiao Tung University Hsin-Chu, Taiwan, R.O.C. (PWINSOR@TWNCTUO1. BITNET) ABSTRACT Pat-Proc, in use at the University of North Texas Center for Experimental Music and Intermedia since 1985, is an interactive pattern/process oriented program originally designed to produce ensemble scores using "minimalist" techniques. Over the years, it has grown into a general compositional utility program which allows wide stylistic latitude. It consists of two parts, a pitch gamut generation routine and a melody generation routine. INTRODUCTION Pat-Proc is an interactive pattern/process oriented program originally written in BASIC and subsequently translated into C. At its inception, the program was designed to output scores (1 to 20 voices) using compositional devices commonly found in so-called minimal music: the application of conceptual, operational, and physical loop processes to user-entered or algorithmically composed melodic material. As the program evolved, however, it became clear that the constituent routines could be used to produce stylistically diverse compositions by allowing maximum flexibility with regard to input data and internal parameter controls. Presently, the program has grown large enough to require interactive execution in two parts: Part 1, which generates and stores a chordal, scalar, or synthetic pitch gamut file for later retrieval by the score compilation routines; and Part 2, which derives, embellishes, loop-processes, and coordinates the melodies which consitute the final score. In broad terms, Pat-Proc now functions as a general compositional utility program with a pattern-processing bias; that is, features have been added which allow the user wide latitude in terms of musical style and the transformation of motivic material. ICMC 114

Page  115 ï~~PROGRAM FUNCTION Part 1 of the program offers three methods of generating a background chord/scale/pitch gamut file: 1. manual entry of a series of articulated aggregates that can be retrieved individually; 2. application by the computer of a constrained intervalsize sieve to generate pitch gamuts; 3. octave-modular or extended pitch scales built (low to high range over the total chromatic) from a user-input interval set (Figure 1.) The program user entered an interval set (5,4,7,3,6), start pitch, start octave, and number of tones in each gamut: L!{U i Chord/gamut-building method 3 Figure 1. Thus, an entire set of registrated background materials for melody derivation and elaboration in Part 2 may be generated in a single execution of Part 1. Naturally, such usage requires a degree of planning prior to the interactive computer session; in practice, some composers choose to build their source file by concatenating shorter program runs or by alternating runs of Parts 1 and 2. Part 2 of the program retrieves the chords/scales/gamuts filed in Part 1, then prompts the user to enter the number of coordinated score voices and the preferred method of assigning part pitch ranges (which may be stratified, interlocking, or comuon to all voices). At this juncture the program invokes the melody writing routine once for each constituent voice and once for each component chord/scale/gamut of the piece. During execution of the routine the user enters formative specifications chosen from the following procedures: * method of melody derivation from chordfile- serial, random-order distribution of available pitches, or minimum/maximum interval choice sieve applied to pitches in the current chord/gamut; ICMC 115

Page  116 ï~~A -i 1 1 tN3 - f~ma~ ted 51t, n:t4es, 5W0"each of rdA 1 r. C 4w -LL C Li = =. 4 - s:5 zoua= c t o is iI,tj!. 1 "i Serial order gamut element selection Figure 2. r 4! tUifl. i-.. I, et-f i f i i i: i!; J i i Ai f tL tI. qaiUf1'[t 1fi Tpi ftJ0 l ' y s s: e Figure 3 * occurrence probability weights for rests, number notes to be embellished and type of embellishment to selected from four available ornaments; (See Figures 2. & of be 3.) * rhythmic complexity level (1-4) ranging from uniform pulse to multiple beat-subdivision (micropulse regrouping) assigned to the derived pitch sequence; (Figure 4.) Rhythm patterns for 2 co-terminating melodies, each having its own internal meter (median): iteian 4= opl exitu level 4 increased plse regr'oup in) A, c.=s! - t 'te 1 vi tI er_________ - } F! 4"1 CD- I i ' e. ve L Y~c~il~xt~ l oel -near rxirtn. pulise -SUMivision/regrrouping) etc. Complex rhythm generation mode Figure 4. * type of rhythmic loop processing to be applied (there are three choices: 1) accretions to a melodic nucleus; 2) progressive subtractions from the total sequence; and, 3) constant-length, metrically justified (among all the ensemble voices), element rotation; (Figure 5.) ICMC 116

Page  117 ï~~Original melody = 8 notes/rests; program user has requested retrograde-order rotation of 2 elements over 16 copies; s s-.............. * pcii armtrst se ftebyteslcd loppoes, pth htm ariuain voueado process-- is to take plac..(Se.igue..). comile an alph anueic n i si S t M SS T"- S",J Paaeereet rotation t pf eseii baSavite digialesynt e orered intop standard notch htm riuationsfwr orpitu andupefranceo tb a ic instruments. Â~?0 nubr fitrton ve- hchte eeted oo PROA OPOTONMATL Ate athorhstcompsrdsevel pees usng Pat-Proc icluing "DulmeaDrm" fot lifsise pin, "rish prformSy avie "Le Synchevirs deisia ynes or, dcr, itoectionsr ndtaSnlavier ad "uintefor ads er"orac becof atrmetden hensotro v spe ctionas um se oeram.eced usingPat-Prc, CpopoIT s, and pERcRaNCe, Sahiue o NewvluYer, 19 *umb umbrduateitueaintshaveralsoichoduedstlctdaloop divrocecoposionske singetheeprogurea5.) COPROROUPTIO, FODPRAT NE cire okNe ok 95 Hiller, Lejaren. EXPERIMENTAL MUSIC, McGraw-Hill, New York, 1959; Jones, Kevin. "Compositional Applications of Stochastic Processes", CMJ, 5:2, 45-61; Lorrain, Denis. "A Panoply of Stochastic 'Cannons"', CMJ, 4:1, 53-81; Winsor, Phil and Gene DeLisa. COMPUTER MUSIC IN C, Windcrest Books, McGraw-Hill, Blue Ridge Summit, PA, 1990. ICMC 117