ALESIS QS8.1 - Manual (Page 122)

Part 8: Editing Programs
110 QS7.1/QS8.1 Reference Manual
T HE V OICE
This digitally-based oscillator provides the actual raw sounds from the 16 megabyte
library of on-board samples. These "raw sounds" can take the form of a simple synth
wave, a multi-sample of a grand piano, an orchestra, or even a full drumkit! The
oscillator’s pitch can be tuned to a fixed frequency or modulated. Modulation is the
process of varying a parameter dynamically over time; the oscillator pitch can be
modulated by an envelope, velocity, pressure, pedal, LFO, and other control sources
(described later). In this manual we frequently refer to the "Sound", which is a
combination of the Voice, the Filter, the Amplitude section, and the various ways of
modulating them.
In their raw forms (such as you would hear after re-initializing the QS) the samples
on the QS have a constant sustaining amplitude, like an organ. In order to shape the
sound so it fades, you would use an envelope or two (keep reading!).
L OWPASS F ILTER
A lowpass filter varies a signal’s harmonic content by progressively increasing
attenuation above a specified cutoff frequency. The higher frequencies are filtered,
while the lower frequencies are allowed to “pass-thru.” When the cutoff frequency is
set high, the sound becomes brighter; when set low, the sound becomes bassier since
fewer harmonics are present.
Static (non-changing) filter settings can be useful, but varying the filter cutoff
dynamically over time often produces more interesting effects. Modulating with
velocity can produce brighter sounds when you play harder, which produces a more
accurate acoustic instrument simulation. Modulating with an envelope can create a
pre-defined change in harmonic structure, such as having a brighter attack and
bassier sustain portion (the point at which the envelope rests before you release the
key).