Alesis QSR 64 manual Voice, Lowpass Filter, Cutoff Frequency, Filter Amplitude Frequency

Editing Programs: Chapter 6

VOICE

This digitally-based oscillator provides the actual raw sounds from the 16 megabyte library of on-board samples. 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 envelope, keyboard, pressure, pedal, LFO, and other control sources (described later).

Note that the waveforms in the QSR are different from those found in samplers or many sample-playback units. Because the QSR has its own filter module and amplitude module for each voice, the pure waveforms are relatively bright--as bright as the original instrument can be--and have a constant sustaining amplitude, like an organ. So if you listen to a piano voice without setting the filter or amp to the correct settings, it won't decay after it is hit, as you might expect. This gives you the freedom to create the timbre and dynamics you want, instead of being chained to the parameters of the original sample.

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.

Cutoff

Frequency

Frequency Response Curve

Filter

Amplitude

Frequency

00 99

The cutoff parameter changes the frequency at which the high- frequency response starts to roll off. Lower values give a lower cutoff frequency. A value of 00 will cut all sound off.

Static (non-changing) filter settings can be useful, but varying the filter cutoff dynamically over time often produces more interesting effects. Modulating with velocity produces brighter sounds with louder dynamics, 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 decay.

QSR Reference Manual 4