/ Examples / Filters / Elliptic

Elliptic

Elliptic implements cascaded IIR filters and a built-in elliptical filter design. It is capable of low-pass, high-pass, or bandpass filtering with very steep slopes. The Atten determines how much of the signal is attenuated outside the passband. Elliptic filters come with a trade-off for their steep slopes: they have a certain amount of ripple outside the passbands. A very small ripple (0.1 or 0.2 dB) produces very little ringing, whereas a large ripple (eg. 20 dB) produces a very strong harmonic ring.

The filter design algorithm sometimes can't fulfill the design criteria -- a particular combination of cutoff frequencies, ripple, and attenuation. If that happens, the user is warned that the filter is not initialized, and the filter is bypassed. This may happen, for instance, if you ask for a very steep attenuation with very low ripple.

FilterType from Lowpass, Highpass, Bandpass.

Atten determines how much of the signal is attenuated outside the passband. Measured in decibels (db). Default is 90.

Ripple sets the filter ripple. MEasured in db. Default .2.

PivotFreq sets the main frequency that characterizes your filter. For Lowpass and Highpass, the pivot frequency represents the end or beginning of the passband. For Bandpass it represents the center frequency of the passband. Measured in Hz.

AttenWidth sets the width of the transition region between the passband and the reject-band. Measured in Hz.

BandWidth sets the width of the passband and is only meaningful for Bandpass. Measured in Hz.

Gain multiplies the signmal before filtering.

Bypass causes the filtering to be skipped and passes through the input signal.

The Example

This example produces an arpeggiating signal run through a Square wave instrument then through the Elliptic filter on its way to the output Channel. In this rig, we are operating Elliptic in Bandpass mode and automate PivotFreq with CCGenerator.