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248 Chapter 22 ES2
Filter Mode (Lo, Hi, Peak, BR, BP)
Filter 1 can operate in several modes, allowing the filtering (cutting away) and/or
emphasis of specific frequency bands.
• A lowpass filter allows frequencies that fall below the cutoff frequency to pass. When
set to Lo, the filter operates as a lowpass filter. The slope of Filter 1 is 12 dB/octave in
Lo mode.
• A highpass filter allows frequencies above the cutoff frequency to pass. When set to
Hi, the filter operates as a highpass filter. The slope of Filter 1 is 12 dB/octave in Hi
mode.
• In Peak mode, Filter 1 works as a Peak Type Filter. This allows for a level increase in a
frequency band, the width of which is controlled by the Resonance parameter.
• The abbreviation BR stands for band rejection. In this mode, the frequency band (a
range of adjacent frequencies) directly surrounding the cutoff frequency is rejected,
whilst the frequencies outside this band can pass. The Resonance parameter controls
the width of the rejected frequency band.
• The abbreviation BP stands for bandpass. In this mode, only the frequency band
directly surrounding the cutoff frequency can pass. All other frequencies are cut. The
Resonance parameter controls the width of the frequency band that can pass. The
bandpass filter is a two-pole filter with a slope of 6 dB/octave on each side of the
band.
Impact of the Filters on the Waveform
Below, you’ll find a number of oscillograms of a sawtooth wave generated by Oscillator
1. These images illustrate the effect of the various modes of Filter 1. The cutoff
frequency was set so that it is equal to the frequency of the first overtone (twice the
frequency of Oscillator 1). The duration and wavelength of this overtone (the second
harmonic) is half as long as the duration and wavelength of the first harmonic (the
fundamental tone).