15
Filters
The most important sound shaping device of every substractive synthesizer is the filter. It cuts off specific
and adjustable frequency ranges and thus overtones, which can result in drastic sonic changes of the
filtered audio material. In the following, you will find a brief description of a filter in general, more detailed
and technical information can be found on page 38 of this manual.
We distinguish between different TYPES of filters: low pass, high pass, band pass and notch:
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Low pass filter cuts off high frequencies and let low frequencies pass.
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High pass filter cuts off low frequencies and let high frequencies pass.
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Band pass filter cuts off high and low frequencies and let a more or less broad frequency bandpass.
A band pass filter is a low pass and a high pass fliter in series.
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Notch filters do the opposite and cuts out a more or less broad frequency band out of the frequency range.
A notch filter is a low pass and a high pass in parallel.
Low pass filters are the most common used for musicial applications and you'll find two in the S1.
To gain most extensive sonic capabilities, the S1 is also equipped with a multi mode filter, that can work as
low-, high-, and band-pass (see page 42).
Next to the filter type, the slope or NUMBER OF POLES defines the characteristics of a filter.
The slope defines how steep the filter cuts off the attenuated frequency range. It is measured in dB/octave
and one pole is equivalent to 6dB/octave. That means, that the most common 4 pole low pass filter cuts high
frequencies with an attenuation of 24dB/octave and more efficient 6 pole filter cuts 36dB/octave.
The steeper the slope, the more effective the filter works (cuts overtones or undertones). Since lower slopes
also produce very musical and sonically useful results, it makes sense to implement filters with switchable
slope. The S1's filters with its two corresponding 3-slope-settings are most versatile and musically useful.
The next basic parameter is the CUTOFF-FREQUENCY or corner frequency. It defines at which frequency
the filter starts to work, respective to attenuates frequencies. On the S1, the cutoff of both filters can be
adjusted from 16Hz to 16kHz (by CUTOFF knob) and has a total frequency range from 5Hz to 30kHz.
Lets have a look on Q-PEAK. This parameter is also known as "resonance" or "emphasis". It boost the
frequencies in the range of the cutoff and makes the tone sound more "cutting". From a certain level on,
the filter starts self-oscillating and works as a sine wave oscillator.
The configuration of LPF and MMF coupled in series and/or in parallel creates a formant filter for various
vocal like sounds.
LOW PASS FILTER
The Low Pass Filter, in 4 pole mode, emulates the familiar low pass filter in some analogue synthesizer.
S1's Low Pass Filter expands sonic potential by adding a unique designed 6 pole low pass mode and quasi
band pass mode.
LPF is characterized by a non-linear transfer function, so-called saturation mode that is affected by the level
of the incoming signal. In the audio mixer the red markings on the potentiometer scales show the level at
which the filter operates in the saturation mode (For more details see LOW PASS FILTER, page 40).
The design quality of LPF's and new features makes the LPF more flexible than any other low pass filter used
in analogue synthesizers and results in qualities, such as:
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CUTOFF, Q-PEAK and output level are voltage controlled
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4 and 6 poles low pass mode (24 dB/octave and 36 dB/octave)
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Qasi Band pass mode (6dB/octave high pass on low side and 24dB/octave low pass on high side)
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Saturable; from "warm" and "smooth" sound (at low to moderate level of incoming signal)
to heavy distorted "nasty" and "aggressive" (at high level of incoming signals)
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Ideal as "effect filter" with external sound material
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Low noise
