(1) CONTROL SECTION: Operation and principles ^
1-2 Dynamic Lowpass Filters (D LPF)
Figure 5 - Dynamic Low Pass
This section of the synthesizer consists of a VCF (Voltage Controlled Filter). It has the function of adding tone color (timbre) to the waveform determined at the SG section (VCO).
With the controls at the normal setting, play a key around the center of the keyboard and gradually turn the fc knob counterclockwise. Note how the sound becomes increasingly rounded in quality. Now turn the peak knob up to "10" and try turning the fc knob. Note how suddenly the tone color changes.
With fc at "10", Peak at "10", and KBD Filter Balance all the way counterclockwise, play the lowest key on the keyboard, a center key, and the highest key. Then vary the fc setting and note how the filters affect the different keys to varying degrees.
Next, turn the KBD Filter Balance all the way up and try the same experiment once more. Note the difference in the effect of the filters on the various keys. The Expand knob controls the degree to which the fc position will vary in proportion to the envelope signal formed by the EM section (to the right).
Try using the Expand knob after you have fully understood the operation of the EM section.
Once the basic waveform has been determined by the VCO and you wish to create a particular quality of sound by means of adjusting the tone color (timbre), a major point to remember is that the tone color may be varied over time. The WF is a type of filter that allows such changes in fc to take place automatically in proportion to input voltage.