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Chapter 5: Oscillators and Filters
124 ANDROMEDA A6 REFERENCE MANUAL
4. The composite output of the PRE FILTER MIX, the Band Pass output of FILTER 1
or the Notch output of the of the POST FILTER MIX can be selected as the input
of
FILTER 2 for additional 4-pole low pass filtering.
The F2 INPUT button is used to route these signals into FILTER 2. Pressing this
button repeatedly switches between
MIX, NOTCH, BP, or nothing as the input to
FILTER 2:
• When
MIX is selected, the source of FILTER 2 is the PRE FILTER MIX—the
oscillators, ring mod and Noise. This is the same signal that goes to
FILTER 1.
So when
MIX is used, you have both a 2-pole multi-mode filter (FILTER 1) and
a 4-pole low-pass filter (
FILTER 2) operating in parallel.
This provides unprecedented capabilities in analog filtering. You now have
the ability to route the same signal to two independent VCFs – with identical
or different modulations.
• When
NOTCH is selected, two things happen:
• the source of
FILTER 2 is only the notch-filtered output of FILTER 1 (which
is the post-fader sum of Filter 1's low-pass and high-pass sections)
• and those two volume controls of Filter 1 are disconnected from a direct
connection to the VCA.
In other words, when
NOTCH is used, you have two parts of a multi-mode
filter (
FILTER 1) and a 4-pole low-pass filter (FILTER 2) connected in series.
Note that you won't hear any output from
FILTER 2 unless either or both of
Filter 1's
HIGH PASS or LOW PASS knobs are up. Only the BAND PASS knob will
send audio from Filter 1 directly to the VCA on its own.
In this case "notch" is a relative term, assuming that both the knobs are up. If
the
HIGH PASS knob is turned fully counter-clockwise, the notch effect is
defeated and the low-pass output of
FILTER 1 is left as the signal. By the same
token, if the
LOW PASS knob is turned fully counter-clockwise instead, the
notch effect is also defeated but the high-pass output of
FILTER 1 remains.
So, in essence, the
NOTCH function can also be considered a low-pass or high-
pass input from
FILTER 1, depending on how the LOW PASS or HIGH PASS
knobs are set.
• When
BP is selected, only the band-pass output of FILTER 1 is input to FILTER
2
. Unlike NOTCH mode, however, the FILTER 1 BAND PASS volume control