THE ELECTRONIC WORKS OF GYÖRGY LIGETI AND THEIR ...

frequencies will not be exact, but rather sounds will begin to taper off at this frequency,
and the rate of this attenuation will vary from filter to filter. 4
Different types of band-pass filters were particularly important for Ligeti’s
compositions, and he often organizes material according to different widths of filtered
noise. Three of the most common levels of filtering are octave-filtered, third-filtered, and
20-Hz-filtered noise. Octave and third-filtered noise would produce bands of noise
approximately an octave or a third of an octave wide; these types of noise would be
generated with specialized filter banks, and were thus used as ways of generating more or
less diffuse bands of noise, rather than for sculpting already generated material. 20-Hz-
filtered noise suggests that a constant number of Hertz was used as a bandwidth rather
than an interval scaled to the octave. Thus bands of 20-Hz noise will seem more compact
in higher registers and more diffuse in the lower registers.
Other studio equipment was also important in the composition of Glissandi, as it
presented Ligeti with a number of ready-made compositional devices. The studio was
equipped with a variable speed tape recorder, with which material could sped up or
slowed down–both transposing the result and lengthening or shortening the segment by
the corresponding interval. Thus an octave (the ratio 2:1) transposition up would result in
a segment half as long as the original. The studio also had devices for generating
impulses, and for techniques such as ring-modulation and reverberation, all of which will
be discussed as they arise in Glissandi and later, in Artikulation.
4
Extensive information on attenuation rates and other aspects of filtering can be found in Peter Manning,
nd
Electronic and Computer Music, 2 ed. (Oxford: Clarendon Press, 1995), esp. 56-61.
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