EURO-SERGE - SYSTEM MODULES
ELBY Designs - Laurie Biddulph
9 Follan Close, Kariong, NSW 2250, Australia
24 of 42
If the
is set with a fast FALL time and a slow RISE time, the
will follow the negative peaks of the sound. Usually these peaks are almost
identical to the positive ones, but not necessarily always. The negative
envelope can be used directly to "shut down" a VCA. This can be useful for
suppressing backgrounds during solos and for inverting dynamics.
Another use of the
is that of a SUB-HARMONIC or UNDERTONE
GENERATOR. This is accomplished by applying a very fast pulse train to the
[TRIGGER IN] and by having an
set to audio frequencies. The
will not respond to a second trigger until its envelope is complete. If the
duration of the envelope is set (manually or with a control voltage) longer that
the time frame between the pulses in the train, it will "skip" one (or more)
pulses. If it misses a single beat, the frequency is lowered by an octave; if it
misses two, the frequency is lowered by an octave and a fifth. Note that this
wave has an inverted trapezoidal shape.
Figure 5.4.14
It is sometimes desirable to shape the envelope so that is has a NON-
LINEAR SLOPE, this is often the case when producing long sustained
sounds or sounds that gradually change in loudness over a long duration.
The
, when patched to the VCA, will see to have little effect on the
loudness of sound at the start and the end of the long envelopes. This is
because of the wide range of the VCA's and the exponential relationship
between the voltage and the amplitude.
By "feeding back" the output of the
to the [VC-IN] and setting the
processing pot to the left, the final output is made non-linear. This
phenomenon occurs because higher voltage to the VC input causes the slope
to decrease, so the
remains longer at the higher voltage levels.
