Alesis QS8.1, QS7.1 manual Voice, Lowpass Filter

Part 8: Editing Programs

THE VOICE

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!).

LOWPASS FILTER

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).

110 QS7.1/QS8.1 Reference Manual