9

Filter Slope
As discussed earlier, a filter will cut off the signal at the set 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. Put another way, you can define how steep the “cliff” is at
the cutoff point by choosing a relatively severe or more gentle slope.
Cutoff frequency
6 dB/Oct 24 dB/Oct12 dB/Oct
Envelopes in the Amplifier Section
The amplifier module of a synthesizer is responsible for controlling the level—or
loudness—of the signal over time.
To put this into a musical context, consider the sound of a violin, which slowly ramps up
to a peak—or maximum—level as the bow is smoothly dragged across a string, is sustained
for a period until the bow is moved away from the string, and then cuts off abruptly. In
comparison, hitting a snare drum with a drumstick results in a very fast peak level, with
no sustain portion, and the sound immediately dies out (although there will be an amount
of decay, the time it takes to fall from the peak level). As you can see, these two sounds
have very different characteristics over time.
Synthesizers emulate these sonic characteristics by providing control over different
parts—the beginning, middle, and end—of a sound’s level over time. This control is
achieved with a component called an envelope generator.
361Appendix Synthesizer Basics