THE ELECTRONIC WORKS OF GYÖRGY LIGETI AND THEIR ...

that brought the piece to its midpoint. The durations of unfiltered material do not
lengthen as regularly as the durations of Section F, which used an additive series to govern
the third stage of accretion, but the trend is clearly towards longer segments. In the first
16.5 seconds (3'46.5"-4'03") of this division, there are no individual segments longer than
one second; from 4'04" on segments as long as 8 seconds are heard. Figure 2.14, A
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spectrograph of Section F displays this trend.
Also visible in the spectrograph is one of the distinct types of filtering used in this
stage. At first, segments are filtered across all registers–perhaps even by replacing
segments of recorded tape with blank leader tape. Later in the piece, however, the
filtering begins to affect only certain registers, passing only the high or low part of the
previous material.
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A previous use of filtering leads us to the first anomaly in Section F ; the space
from 3'29-3'36.5" involved an abrupt cut-off in the upper-middle register from 1300 to
4735 Hz. One would expect to find a corresponding window in this register during a span
from 3'56.5-4'04", which is equally spaced 10 seconds from the center. This window,
however, does not occur. As shown in the spectrograph below, Figure 2.15.
Since the material from Section A is, at this point, entirely below 1200 Hz, it will
not impinge on this window, yet there are clearly bands of noise that stretch from the low
register well into this area; these are most likely extensions of the low noises of Event 5.
In the first half, Ligeti achieved a cut-off and the resulting window by abruptly using a
band-stop filter to remove signals in this range, but this must have been done at a late
stage of the composition, since, in the second half (and amongst all of the other filtering)
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