Akai MPC User Manual page 275

MIDI messages enable you to manipulate the behavior of a sound generator to a
Control Change
significant degree. This message essentially consists of two components:
(Controllers)
Controllers can be used for effects such as slowly swelling vibrato, changing the
stereo panning position and influencing filter frequency.
Cutoff The cutoff frequency is a significant factor for filters. A low-pass filter for example
dampens the portion of the signal that lies above this frequency. Frequencies
below this value are allowed to pass through without being processed.
Decay Decay describes the descent rate of an envelope once the Attack phase has
reached its maximum and the envelope drops to the level defined by the Sustain
value.
An envelope is used to modulate a sound-shaping component within a given time.
Envelope
For instance, an envelope that modulates the cutoff frequency of a filter opens and
closes this filter over a period of time. An envelope is started via a trigger, usually a
MIDI Note. The classic ADSR envelope consists of four individually variable
phases: Attack, Decay, Sustain, and Release. Attack, Decay and Release are
time or slope values, while Sustain is an adjustable level. Once an incoming trigger
is received, the envelope runs through the Attack and Decay phases until it reaches
the programmed Sustain level. This level remains constant until the trigger is
terminated. The envelope then initiates the Release phase until it reaches the
minimum value.
A filter is a component that allows some of a signal's frequencies to pass through it
Filter
and dampens other frequencies. The most important aspect of a filter is the filter
cutoff frequency. Filters generally come in four categories: low-pass, high-pass,
band-pass, and band-stop. A low-pass filter dampens all frequencies above the
cutoff frequency. A high-pass filter in turn dampens the frequencies below the
cutoff. The band-pass filter allows only those frequencies around the cutoff
frequency to pass; all others are dampened. A band-stop filter does just the
opposite; it dampens only the frequencies around the cutoff frequency. The most
common type is the low-pass filter.
• The controller number, which defines the parameter to be influenced. It can
range from 0 to 127.
• The controller value, which determines the extent of the modification.
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