In this chapter we will have a closer look at the synth modules used in the different
voices.
5.1. OSCILLATOR
The oscillators provide 6 different waveforms:
> Sine
> Triangle
> Saw
> Rectangle
> Noise
> PWM
The waveforms are classic analogue waveforms realized using bandlimited wavetable
oscillators.
5.2. FILTER
The filter is a 2 pole (12dB) state variable filter (SVF). It's used to shape the harmonic
content of the sound. For example a hihat sound consists of high frequencies and no
low frequencies, so you want to use a highpass filter. A clap has lots of mid sounds,
here a bandpass filter is useful.
There are 3 parameters that control the filter response. Frequency, resonance and
drive.
FREQUENCY
The frequency determines the operating point of the filter in the spectrum.
For example a low pass filter will cut off all frequencies above its set cutoff
frequency (all frequencies below it pass the filter unaltered – hence the name).
RESONANCE
The resonance controls the feedback path of the filter. With higher resonance
settings the frequencies around the operating point (i.e. the set frequency) will
be amplified more and more.
It becomes clear if we look at the filter amplitude response plots in the next
section.
DRIVE
Controls how 'hot' the filter is driven. More drive yields in more distortion. In the
normal operating range, when drive is set to 0, the filter is quite clean and nearly
linear. With higher input levels/drive settings, a soft clipper as well as the slew
rate limit of the integrators comes into effect. Low settings will only affect the
resonance peaks, higher settings will distort the whole signal. Since the soft
clipper is scaling down excessive peaks in the signal, the audible resonance is
reduced with higher drive settings.
FILTER TYPES
There are several different filter types available, each with it's own characteris-
tics. Let's have a closer look at each one of them. The filters are plotted with 3
different resonance settings. No resonance, medium and high. The cut off
frequency is the same in every plot and marked by the vertical dashed line.
The x axis shows the frequency from 0Hz to 22kHz, the y axis shows the gain for
the specific frequency - Both on a logarithmic scale.
Highpass
The highpass filter removes low frequencies from the signal. All frequencies below
the cutoff frequency are reduced gradually.
Lowpass
The lowpass filter removes high frequencies from the signal. All frequencies above
the cut off frequency are reduced gradually.
18 dB
12 dB
6 dB
0 dB
-6 dB
-12 dB
-18 dB
18 dB
12 dB
6 dB
0 dB
-6 dB
-12 dB
-18 dB
LXR EURORACK MODULE OWNERS MANUAL
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