Moog System 15 Instruction Manual page 14

3. Turn off the MIXER control A and turn up MIXER controls B and C. Obtain any desired
interval between the 921B OSCILLATORS by varying the FREQUENCY and RANGE con-
trols. Play the keyboard.
4. Manipulate the FIXED CONTROL VOLTAGE, RANGE, and REGENERATION controls
of the 904A LOWPASS FILTER; note the effect of each on the audio signal. The FIXED
CONTROL VOLTAGE determines the cutoff point of the filter, REGENERATION empha-
sizes the cutoff point, and RANGE determines the portion of the audio spectrum available for
filtering.
5. Turn down the FIXED CONTROL VOLTAGE of the 902. Play the keyboard. The 902 is
now articulating the tones.
Of course, any of the filters can be used in conjunction with any of the audio signals, includ-
ing externally produced tones. Experiment with all possible combinations of tone sources and
filtering.