Specifications

SUBTRACTOR SYNTHESIZER
108
D Notch
A notch filter (or band reject filter) could be described as the opposite of a
bandpass filter. It cuts off frequencies in a narrow midrange band, letting the
frequencies below and above through. On it’s own, a notch filter doesn’t re-
ally alter the timbre in any dramatic way, simply because most frequencies
are let through. However, by combining a notch filter with a lowpass filter
(using Filter 2 - see page 109 in this chapter), more musically useful filter
characteristics can be created. Such a filter combination can produce soft
timbres that still sound “clear”. The effect is especially noticeable with low
resonance (see page 108) settings.
The darker curve illustrates the roll-off curve of the Notch Filter. The lighter curve in the
middle represents the filter characteristic when the Resonance parameter is raised.
Filter 1 Frequency
The Filter Frequency parameter (often referred to as “cutoff”) determines which
area of the frequency spectrum the filter will operate in. For a lowpass filter, the
frequency parameter could be described as governing the “opening” and “clos-
ing” of the filter. If the Filter Freq is set to zero, none or only the very lowest fre-
quencies are heard, if set to maximum, all frequencies in the waveform are heard.
Gradually changing the Filter Frequency produces the classic synthesizer filter
“sweep” sound.
! Note that the Filter Frequency parameter is usually controlled by
the Filter Envelope (see page 110) as well. Changing the Filter Fre-
quency with the Freq slider may therefore not produce the expected
result.
Resonance
The filter resonance parameter is used to set the Filter characteristic, or quality.
For lowpass filters, raising the filter Res value will emphasize the frequencies
around the set filter frequency. This produces a generally thinner sound, but with
a sharper, more pronounced filter frequency “sweep”. The higher the filter Res
value, the more resonant the sound becomes until it produces a whistling or
ringing sound. If you set a high value for the Res parameter and then vary the fil-
ter frequency, this will produce a very distinct sweep, with the ringing sound be-
ing very evident at certain frequencies.
• For the highpass filter, the Res parameter operates just like for the lowpass
filters.
• When you use the Bandpass or Notch filter, the Resonance setting adjusts
the width of the band. When you raise the Resonance, the band where fre-
quencies are let through (Bandpass), or cut (Notch) will become narrower.
Generally, the Notch filter produces more musical results using low reso-
nance settings.
Filter Keyboard Track (Kbd)
If Filter Keyboard Track is activated, the filter frequency will increase the further
up on the keyboard you play. If a lowpass filter frequency is constant (a Kbd set-
ting of “0”) this can introduce a certain loss of “sparkle” in a sound the higher up
the keyboard you play, because the harmonics in the sound are progressively
being cut. By using a degree of Filter Keyboard Tracking, this can be compen-
sated for.