Computer Music Produced with the Aid of a Digital-to-Analog Converter

Leonardo, Vol. 11, pp. 3940. Pergamon Press 1978. Printed in Great Britain COMPUTER MUSIC PRODUCED WITH THE AID OF A DIGITAL-TO-ANALOG CONVERTER Frank Brown* 1. Automatic music composition The use of a digital computer in conjunction with a digital-to-analog converter (DAC) for composing music is an exciting possibility. With the aid of appropriate computer programs, a computer can compose musical scores that, after suitable conversion, can be heard as sounds. The Group BBK (composed of Pierre Barbaud. Frank Brown and Genevieve Klein)isconcerned with producing musical works by procedures in which human involvement is minimal. Barbaud has described his technique for automatic music composition in his books [1,2] and in numerous articles. The computer programs that he has written can produce either musical scores of a traditional type in a harmonic or contrapuntal style intended for musicological studies or psychological experiments, or musical scores that I consider to be leading examples of computer music. He has prepared numerous computer programs for computer music under the general title TERRA IGNOTA (Fig. 1). As the title suggests, the programs involved musical sounds that cannot be produced by traditional musical instruments. 2. Writing traditional scores Among the computer programs written by the group, the one called ‘SCRIPTU’is the most suitable for codinga traditional musical score (Fig. 1). It is the only program by the Group written in Cobol language, a computer language that emphasizesorganization. A wide variety of means of transcription is provided and a score can be produced on magnetic disk by the computer. An example of two measures of a piece of music is shown in Fig. 2. It is represented in SCRIPTU language (French version) as follows: TO4 D02;M 12;S02;D03 102 R04 B01, TO8 I01 D04, S04, I05 T32 D04. I02 R04 B01, I01 PO2 TO2 F#4, S04, F#4, TO4 S04, LA4. CHORDS SCORE END The notes are represented by the tones DO, MI, SO, F# and LA. Two Instruments, I, are designated by numbers 01 and 02. R stands for ‘repeat’; 04 following R means ‘repeat four times’. T indicates relative time duration; here there are durations of 02, 04, 08 and 32. Similarly, PO2 represents a relative time duration of silenceequal to 02. B represents a chord, and 01 signifies the first chord (the first line listed under ‘chords’). A comma entered between two notes indicates that they are sounded successively;a semicolon indicates that they are sounded simultaneously. A period punctuation mark indicates the end of the measure. The designation T32 DO4 states that the tone DO4 has a relative duration of time 32, which means it sounds during the two measures. The following is another example: CHORDS EXP SCORE I01 DOO,R85 B01. END Trditiord m C 0 I cornputer wagram in outornatic cornPosition SCRIPTU computer program for t r a d i t i o n a l cornposition Numerical d i s k N D I T U canputer program dealing w i t h the synthesis of sounds e w ! 3 k a I 0 u LWD SPEAKER DIGITAL-TOCONVERTE R Fig. I. Diagram showing the several steps in producing computer music with the aid of a digital-to-analog converter (DAC). I *Physicist, 15 Rue de la Lancette,75012 Paris, France.(Based on text in French) (Received 23 July 1976) 39 Fig. 2. Two measures of a musical score. 40 Frank Brown Here, in the absence of other statements, the parameter EXP raisesthe preceding tone by a halftone. thus one can produce all the tones on thepiano beginningwith the tone (DO0 = 32 Hz,. ..DO3 = 256Hz by halftones;85 measures are to be produced. If a semicolonfollowed B01, then the 85 tones would be sounded simultaneously. The scores are recorded on a magnetic disk in the computer (Fig. 1).They are 'numerical musical scores' in which notes are specified by five parameters: frequency, amplitude, duration, starting time and instrument (designated by number). 3. Program AUDITU Program AUDITU serves for converting information provided by the score on the magnetic disk into sound produced by an electronic DAC [3,4]. It employs very rapid recursive mathematical generators: Y;+I= 2a (cos 0) Yt - a2Y...