Operation Manual

6.31 Keyboard 97
This module is to invert the control voltage generated by an ADSR so that the cutoff frequency
of a VCF module first goes down when triggering a new note as shown in Figure 50. The inverter
can also be used to obtain a stereo tremolo effect (amplitude modulation) as illustrated in Figure 51.
Figure 51: Stereo tremolo effect.
6.31 Keyboard
The Keyboard module simulates the outputs of a classic monophonic analog
high-note priority keyboard. It has no input and two outputs. The first output is the
gate signal. It is equal to 0 Volt when no key is played, and 1 Volt when one or more
keys are played. The second output signal is the pitch signal. Its value corresponds
to the highest key played when one or more keys are depressed and to the last key
played when no key is depressed. The pitch signal varies by ±1 Volt per octave
which implies a change of 1/12 Volt for a pitch variation of 1 semitone. The pitch
signal is calculated with respect to the C3 key (middle C) which outputs a value of
0 Volt. This means that, for example, the C2 key signal is -1 Volt and that of the C4
key is +1 Volt. The stretch knob on the interface is used to simulate stretched tuning
used on instruments such as pianos. Turned to the left, low notes will be tuned higher and high
notes lower (inner stretch); turned to the right, low notes will be tuned lower and high notes will be
higher (outer stretch). In the center position, the tuning will be equal. The error knob introduces
some randomness in the pitch signal. Turned to the left, no error is outputted and the pitch signal
is perfect; as the knob is turned to the right, errors will start to appear causing small fluctuations in
pitch. The effect of this knob is to simulate pitch variations found in analog synths.
The default value of the following parameters is set at construction
• pitch wheel range: determines the range of pitch variations that can be obtained with the
pitch wheel. The convention is 1 Volt/octave (maximum value is 2 Volts). A semitone is
equal to a 0.08333 value.
• MIDI channel: MIDI channel used by the keyboard.