User Guide
16
FILTER
Grandmother relies on a classic -24dB/octave Moog Low Pass
Ladder Filter. The term “Ladder” stems from the hardware design
of the original lter, which has transistors wired in a type of ladder
conguration. Low Pass indicates that the Filter is selectively removing
harmonic content in the upper part of the audio spectrum, while
allowing the lower frequencies to pass unaffected - this is the essence
of a low pass lter, and the foundation of subtractive analog synthesis.
Finally, the -24dB specication indicates how frequencies are
attenuated above the Cutoff frequency. In this case, harmonic content
is rolled off at a rate of -24dB per octave.
CUTOFF
The CUTOFF knob species the frequency at which the Filter
begins to attenuate (or reduce) harmonic content, from 10Hz to
20kHz. Harmonic content occurring above the Cutoff frequency
is attenuated, while sounds occurring below the Cutoff frequency
will pass through unaffected. As the Cutoff frequency is lowered,
less harmonic content is able to pass, resulting in a progressively
darker sound. Raising the Cutoff frequency opens the Filter, and
more harmonic content is able to pass, creating a progressively
brighter sound.
NOTE: Filter Cutoff is one of the most effective parameters to apply modulation to. Doing so allows
the sound to have motion and character, without interfering with the ability to play “tonal” music in the
way that applying modulation to the Oscillators’ frequency might.
KBD TRACK
Keyboard Tracking allows the value of the note played on the keyboard to
also affect the Cutoff frequency of the Filter. Higher notes on the keyboard
will be perceived as being brighter than notes played lower on the keyboard.
This is how many acoustic instruments sound in nature; higher pitched notes
have more upper harmonic energy and appear to be brighter.
1:2
In the 1:2 position, the value of the note played on the keyboard will affect
the Cutoff frequency at half of its full value. This means that playing a note two octaves above
another will only raise the Cutoff frequency by one octave.
OFF
In the OFF position, the keyboard Tracking is off, and the value of the note played on the keyboard
will have no effect on the Cutoff frequency.
20Hz 20kHz
200Hz 2kHz
+
-
20Hz 20kHz
200Hz 2kHz