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RissetFilters
Applies continuously ascending or descending sweeping bandpass filters - a filtering version of RissetTones.
RissetFilters is a variation of the RissetTones contraption. Both contraptions produce the acoustic illusion of a gliding tone (glissando) that seems to move continuously up or down in pitch. RissetFilters applies this sweeping effect to a sound input by filtering it with bandpass filters. The effect created by RissetFilters is similar to that of a flanger or phaser, except that instead of sweeping up and down, the filters sound as if they are always sweeping in one direction.
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See the Adjusting Contraption Properties section for information about using sliders, knobs, presets etc. |
Related Contraptions
RissetTones, Nebuliser, 5Combs
Parameters
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Rate |
Controls the speed and direction of the center frequencies of each bandpass filter in the filter bank. Rate ranges from -5 to 5 Hz. At 0 Hz (default) the filter's center frequencies are stationary. Negative Rate values produce a continually descending sweep. Positive Rate values produce a continually ascending sweep. |
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Spacing |
Defines the distance between the center frequencies of each successive bandpass filter. |
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Range |
Defines the upper and lower limits of the bell-shaped frequency versus amplitude envelope applied to each filter band. |
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Max Filts (MaxFilters) |
Defines the maximum number of filters utilized within the filter bank. This can be used to limit the maximum CPU load consumed. If you choose a figure that matches the required value (on the right of the text box), the sweeping illusion will be maintained. Higher settings won't have any effect, and lower settings create irregularities and gaps in the filter bank. |
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Q (FilterQ) |
Determines the ratio of filter bandwidth to frequency. Higher values of Q lead to narrower filter bands, which can sound like whistling tones, and make the sweeping effect more obvious. Higher Q values can also result in less input signal being passed by the filters, which can lead to low output levels. Correct this by adding a Gain contraption to your patch. |
Relevant Example Files
The following files provide some examples of how RissetFilters can be used:
RissetSquelchBass.amh & OvertonesAutomation.amh
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To open the Example Files directory, go to the File menu, select Open, and double-click on the Examples folder. Read descriptions of the example files here. |
Suggested Uses and Practical Applications
Steve Adam says: “RissetFilters can be useful in providing cyclic variations in otherwise relatively static textures.”
Warren Burt says: “Have a static drone of several pitches go through the Risset Filters. Have a low positive Rate (ca 0.191 for example), very close spacing of the bands, a low range that the bands move through, and Hi Q. This will create a sense of harmonic tension rising (the axe murderer approaches slowly....heh heh heh) without the listener necessarily being aware that the filter pitch is rising.”
Technical Discussion
The Shepard/Risset tone illusion has been likened to the aural equivalent of the “barber shop pole” on which spiraling lines appear to continuously move from one end of the pole to the other as it spins.
RissetFilters uses a bank of bandpass filters in place of the oscillator bank used in RissetTones. As the center frequencies of the bandpass filters are evenly spaced a kind of comb filter is created.
Larger Spacing settings and/or narrower Range settings will reduce the number of filters required by the effect, and hence the CPU load required. Similarly, smaller Spacing or a wider Range will require more filters and hence will use more CPU.
Historical Background
RissetFilters is based on the same principle as the RissetTones contraption, implementing a variation of the acoustic illusion originally developed by Roger Shepard in the 1960s and later developed by Jean-Claude Risset.
The idea for a Risset filter bank was introduced to the creator of AudioMulch by Steve Adam who designed the effect for use in his composition Chromophony.
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