ARRAS (1980)

for four computer-synthesized soundtracks

Arras refers metaphorically to the heavy wall hanging or tapestry originally produced in the French town of the same name. The threads running through the material form both a background and, when coloured, a foreground pattern as well, even when they are the same thread. In the piece there is a constant ambiguity between whether a component sound is heard as part of the background texture, or whether it is heard as a foreground event because, in fact, the frequencies are the same. The listener can easily be drawn into the internal complexity of the constantly shifting pattern, but at the same time can sense the overall flow of the entire structure.

Arras is a continuously evolving texture based on a fusion of harmonic and inharmonic spectra. The large-scale structure of the piece follows a pattern of harmonic change going from closely spaced odd harmonics through to widely spaced harmonics towards the end. Each harmonic timbre is paired with an inharmonic one with which it shares specific harmonics, and with which it overlaps after each twenty-five second interval. This harmonic/inharmonic structure forms a background against which specific events are poised: shorter events, specific high pitches which otherwise would be imbedded in the overall timbre, and some percussive events. However, all frequencies found in the foreground events are the same as those in the background texture; hence the constant ambiguity between them.

Arras received an honourable mention in the computer music category of the 1980 International Competition of Electroacoustic Music sponsored by the G.M.E.B. in Bourges, France.

Arras is available on the Cambridge Street Records CD Pacific Rim, and the RCI Anthology of Canadian Electroacoustic Music.

Sound Example available

HARMONIC - INHARMONIC RATIOS USED IN ARRAS



PAIRS OF RATIOS WITH COMMON PARTIALS




BACKGROUND TEXTURE
Structure of overlapping envelopes in three layers based on three different fundamental frequencies, F1 (50 Hz), F2, F3. This unit structure (with 18 enveloped events, each doubled for a slight choral effect) in turn overlaps with its successor (dashed lines) after 25 seconds and returns to the first ratio after another 25 seconds (e.g. 1:2 -> 3:8 -> 1:2 -> 1:3 ....). 22 ratios are used, hence the background structure is composed of 792 separate events.

FOREGROUND ELEMENTS
- High frequencies (those above 800 Hz) chosen from sideband sets

- Short events (0.21 sec) chosen from all sideband frequencies, distributed in a Poisson distribution of about 4 events/sec

 - Enveloped spectra using c:m family members on a common fundamental (50 Hz); three-part envelopes are (2.0, 0.5, 4.0), (0.76, .01, 1.24) and (0.01, 0.2, 1.2) sec.



- Frequency-time structure of events shown as horizontal lines lying within a tendency mask frame centred on frequencies F4, F5



Spectrogram of the middle section of the work
Note: Sound examples of all of the above elements available from the composer (truax@sfu.ca).

Reference:

B. Truax, "Timbral Construction in Arras as a Stochastic Process", Computer Music Journal, 6(3), 1982.

Production Note:

The work was realized with the composer's POD6 and POD7 programs for computer sound synthesis and composition at Simon Fraser University. All the component sounds are examples of frequency modulation (FM) synthesis, generated in binaural stereo, with both amplitude and time differences between channels. However, considerable digital mixing, and later analog mixing in the Sonic Research Studio, produced the resulting complex texture.

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