Low Pass Filter

Purpose

Passes the frequency components of the input signal that are below the filter cutoff frequency while attenuating the frequency components above the cutoff frequency.

Controls

Overload

Indicates an overload condition in the filter.

Invert

Inverts the polarity of the signal passing through the device.

Mute

Mutes the output of the filter.

Corner Frequency

Adjusts the filter cutoff or corner frequency.  Signal components below this frequency are passed, components above are attenuated.

Level

Adjusts the pass band gain through the device.

Setup... Block

Filter Type

Selects the filter Response Characteristic.

Note: When the Linkwitz-Riley Filter Type is selected, Filter Slopes are only available in even multiples of 12dB/octave.  Slope control settings may be changed when the filter type is switched to Linkwitz-Riley to enforce this constraint.  Slope settings will not be restored when switching back to Butterworth or Bessel filter types.

Slope

Controls the steepness of the filter roll-off between the pass band and the stop band.

For Butterworth or Bessel Filter Types, 6dB/octave to Maximum Slope in 6dB/octave increments.  For Linkwitz-Riley Filter Type, 12dB/octave to Maximum Slope in 12dB/octave increments.

Graph... Block

Graphical Frequency Response

Displays the frequency response of the filter. See the EQ Curve Graphics Display documentation for a complete description.

Frequency Response

Amplitude Response for a Low Pass Filter.

Phase Response for a Low Pass Filter.

Legend

Butterworth (red solid)

Bessel (blue dotted)

Linkwitz-Riley (black dashed)

Advanced Topic

The processing power required by Low Pass filters is proportional to the maximum slope of the filter.  The maximum slope is determined by an argument in the Algorithm String.  The Algorithm Strings have the following form.

LOWPASS N

Where N is the filter slope in dB/Octave.  Legal values are 12, 24, 36, 48, 60. Due to the implementation of the filters, odd order filters (6, 18, 30, 42, 54dB/Octave) are as expensive in terms of signal processing power as the next steeper even order filter.  Odd order maximum slope settings are thus not supported.