10.6

713Logic Pro Instruments
Filter slope
A filter cuts off the signal at the specified cutoff frequency. This cutoff doesn’t happen
abruptly but rather at a given slope, which is measured in decibels (dB) of gain reduction
per octave. You can define how steep the “cliff” is at the cutoff point by choosing a severe
or gentle slope.
Envelopes in the amplifier
Amplifier envelope overview
The amplifier module of a synthesizer is responsible for controlling the level, or loudness,
of the signal over time.
Consider the sound of a violin, for example. The sound slowly ramps up to a peak, or
maximum, level as the bow is dragged across a string, then it is sustained for a period until
the bow is moved away from the string, at which point it cuts off abruptly.
In contrast to the violin example, hitting a snare drum with a drumstick results in a very fast
peak level with no sustain portion, then the sound immediately dies out—although there is
some decay, the time it takes to fall from the peak level.
These two sounds clearly have different characteristics over time.
Synthesizers emulate these sonic characteristics by providing control over different parts—
the beginning, middle, and end—of the sound level over time. This control is achieved using
a component called an envelope generator.
Note: Envelope generators are not limited to controlling signal amplitude. They can
also control the rise and fall of the filter cutoff frequency or they can modulate other
parameters. In short, envelope generators can be used as a modulation source—or as a
“remote control” for a given parameter. See Modulation overview.