User Manual

24
The Filter Section
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The sum of the various signal sources created in the mixer is fed to the Filter Section, which
can be used to modify the harmonic content of the Oscillator’s output. Peak’s filter is a
traditional analogue design, and has an extensive set of modulation and control options.
Filter type
The Shape button
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selects one of three filter types: low-pass (LP), band-pass (BP) or
high-pass (HP)
The Slope button
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sets the degree of rejection applied to out-of-band frequencies;
the 24 dB position gives a steeper slope than the 12 dB; an out-of-band frequency will be
attenuated more severely with the steeper setting.
Volume
Volume
Frequency
Cutoff
Frequency
Cutoff
Frequency
Frequency
Cutoff
Frequency
Cutoff
Frequency
Volume
Volume
Frequency
Frequency
Low Pass 24 dB
Low Pass 12 dB
High Pass 24 dB
Band Pass 12 dB
Frequency
The large rotary Frequency control
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sets the cut-off frequency of the filter when Shape
is set to HP or LP. With BP selected, Frequency sets the centre frequency of the filter’s
pass-band.
Sweeping the filter frequency manually will impose a “hard-to-soft” characteristic on almost
any sound.
Resonance
The Resonance control
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adds gain to the signal in a narrow band of frequencies
around the frequency set by the Frequency control. It can accentuate the swept-filter
effect considerably. Increasing the resonance parameter is very good for enhancing
modulation of the cut-off frequency, creating a very edgy sound. Increasing Resonance
also accentuates the action of the Frequency control, giving it a more pronounced effect.
Volume
Frequency
Cutoff
Frequency
Low Pass 24 dB
with Resonance
Setting Resonance to a high value can greatly increase the output signal level – the synth
volume. This can be compensated for by adjusting VCA Gain
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.
Filter modulation
The filter’s Frequency parameter may be modulated - using the physical controls - by the
output of LFO 1, the Amplitude Envelope, Modulation Envelope 1, or any combination of
these. Modulation by LFO 1 is controlled by the LFO 1 depth control
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, and by the Env
Depth control
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for either of the two envelopes. The Env Depth control is assigned
to the Amplitude Envelope by selecting Amp Env with the Source button
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, and to
Modulation Envelope 2 by selecting Source to Mod Env. Both mod sources may be used
simultaneously, with the Env Depth control adjusting only the currently selected envelope.
(Compare with the use of LFO 1 and Mod Env 1 for modulating the Oscillator’s Shape
parameter.)
As with many other control routings between synth sections, a great many more options for
modulating the filter may be explored using the Modulation Matrix (see page 26).
Note that only one LFO – LFO 1 - is used for filter modulation. Filter frequency can be
varied by up to eight octaves.
Negative values of LFO 1 depth “invert” the modulating LFO waveform; the effect of this
will be more obvious with non-sinusoidal LFO waveforms and low LFO rates.
Modulating the filter frequency with an LFO can produce some unusual “wah-wah”
type effects. Setting LFO 1 to a very slow speed can add a gradual hardening and then
softening edge to the sound.
When the filter’s action is triggered by an envelope, the filter action changes over the
duration of the note. By adjusting the Envelope controls carefully, this can produce some
very pleasing sounds, as for example, the spectral content of the sound can be made to
differ considerably during the attack phase of the note compared to its “fade-out”.
Env depth lets you control the “depth” and “direction” of the modulation; the higher the
value, the greater the range of frequencies over which the filter will sweep. Positive and
negative values make the filter sweep in opposite directions, but the audible result of this
will be further modified by the filter type in use.
Peak also allows direct modulation of the Filter frequency by Oscillator 3, to a degree
controlled by Osc 3 Filter Mod
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. The intensity of the resulting effect is dependent on
the control setting, but also on almost all Osc 3 parameters, e.g., range, pitch, waveform,
pulse width and any modulation applied to the Oscillator.
Try adding Osc 3 Filter Mod while sweeping Osc 3 pitch with the pitch
wheel.