DSP Functions
Filters
14-21
This is a three-stage function that puts two notches in the frequency response. As with NOTCH
FILTER and NOTCH2, there are control input pages for frequency and width. A third control
input page affects the separation of the notches.
Setting the center frequency on the F1 FRQ page deÞnes the frequency thatÕs halfway between
the notches. The settings for the separation affect the behavior of the width control parameters.
When the separation is 0, the notches are close to the center frequency, and the width control
parameters control the widths of both notches equally. Positive values for separation move the
notches apart, and cause the width control parameters to affect the width of the higher-
frequency notch more than the width of the lower-frequency notch. Negative values for
separation will move the notches apart to the same extent, but will cause the width control
parameters to affect the width of the lower-frequency notch more than the width of the higher-
frequency notch.
Twin Peaks Bandpass Filter (TWIN PEAKS BANDPASS)
The control parameters for TWIN PEAKS BANDPASS work the same way as for DOUBLE
NOTCH FILTER, but of course, you get peaks instead of notchesÑthat is, the amplitudes of
partials near the center frequency are high, and the amplitudes are increasingly attenuated at
frequencies farther from the center.
-60
-50
-40
-30
-20
-10
0
10 100 1000 10000 100000
Frequency in Hertz
Amplitude in dB
Center frequency = C 7;
separation = 1 octave;
width at .5, 1, 2 octaves
2
1
.5
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