Digital Sound & Music: Concepts, Applications, & Science, Chapter 6, last updated 6/25/2013
26
Figure 6.26 Envelope controls on a synthesizer
Envelopes can be used to control almost any synthesizer parameter over time. You might
use an envelope to change the cutoff frequency of a filter or the pitch of the oscillator over time.
Generally speaking, if you can change a parameter with a slider or a knob, you can modulate it
over time with an envelope.
MIDI Modulation 6.1.8.8
You can also use incoming MIDI commands to modulate parameters on the synthesizer. Most
synthesizers have a pre-defined set of MIDI commands it can respond to. More powerful
synthesizers allow you to define any MIDI command and apply it to any synthesizer parameter.
Using MIDI commands to modulate the synthesizer puts more power in the hands of the
performer.
Here’s an example of how MIDI modulation can work. Piano players are used to getting
a different sound from the piano depending on how hard they press the key. To recreate this
touch sensitivity, most MIDI keyboards change the velocity value of the Note On command
depending on how hard the key is pressed. However, MIDI messages can be interpreted in
whatever way the receiver chooses. Figure 6.26 shows how you might use velocity to modulate
the sound in the synthesizer. In most cases, you would expect for the sound to get louder when
the key is pressed harder. If you increase the Amp knob in the velocity section of the synthesizer,
the signal amplifier level increases and decreases with the incoming velocity information. In
some cases, you might also expect to hear more harmonics with the sound if the key is pressed
harder. Increasing the value for the F.Env knob adjusts the depth at which the filter envelope is
applied to the filter cutoff frequency. A higher velocity means that the filter envelope makes a
more dramatic change to the filter cutoff frequency over time.
Figure 6.27Velocity modulation controls on a synthesizer
Some MIDI keyboards can send After Touch or Channel Pressure commands if the
pressure at which the key is held down changes. You can use this pressure information to
modulate a synthesizer parameter. For example, if you have a LFO applied to the pitch of the
oscillator to create a vibrato effect, you can apply incoming key pressure data to adjust the LFO
amount. This way the vibrato is only applied when the performer desires it by increasing the
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