Alesis QSR 64 manual About Signal Processing, Lfo Low Frequency Oscillator, Envelopes

Editing Programs: Chapter 6

LFO (LOW FREQUENCY OSCILLATOR)

The pitch, filter, and amp modules each have a dedicated LFO module for modulation. The term LFO stands for low frequency oscillator, and comes from how modulation was created in the early synth days (an oscillator set to a low frequency could modulate some aspect of the sound; routing the LFO to the pitch, for example, would create vibrato). The LFO creates a cyclic (periodic) modulation; this amount can be constant and/or varied with a variety of modulation sources (mod wheel is one of the most popular). Each LFO has a waveform shape and speed, along with other controls.

ENVELOPES

Envelope generators provide a modulation signal that varies over time, from the time you strike the key until after you let go. There are three independent envelope generators (for pitch, filter, and amp) in each Program Sound. An envelope generator has different effects on different modules. Example: The Amp Envelope creates level changes. Amplitude that decays over time creates percussive effects (plucked strings, drums, etc.). Amplitude that increases over time gives the effect of brass, woodwind, and some bowed instruments.

Each envelope generator has the standard attack, decay, sustain, and release parameters found on most synthesizers, along with delay, sustain decay, and different triggering options.

		DECAY
		SUSTAIN LEVEL
L		RELEASE
E
V DELAY		ATTACK
E		SUSTAIN DECAY
L
	TIME
NOTE ON		NOTE OFF

ABOUT SIGNAL PROCESSING

The QSR features a signal processing section based on the Alesis QuadraVerb 2. It is a complete digital signal processing unit with four input buses, simultaneous multiple effects, and flexible signal routing.

Sound

Sends 1—4

Main L

Aux L

Main R

Aux R

Effects

Processor

(reverb, delay, chorus, etc.)

Effects parameters are edited separately from either the Program or the Mix, using Effects Edit Mode (more in Chapter 6). In Program Edit Mode, each of the four sounds in the Program has its own Effect Level control and can be assigned to any one of the four effect buses. Effects settings, Effect Level and Bus information are saved with the Program when you store it back into memory.

QSR Reference Manual 6