IIR Z Filter

A Biquad IIR filter with mouse adjustable pole and zero controls.

Pins

io	letter	name	unit	description
in	X	input	auto	signal to filter
	A	attenuation	auto	post gain
out	=		auto	filtered signal

Controls

name	description
X	pole, emphasize
O	zero, reduce

Parameters

name	option	key	description
mode	highpass	h	selects the type of filter
	bandpass	b
	lowpass	l
scale	linear	n	selects the angular frequency display mode
	logrithmic	g
display	detailed	d	show the filter characteristics
	small	enter	show the object as an icon
	show clipping	c	show saturation with red ring

Notes

The Z plane is commonly used in digital filters. Is is a polar representation of frequency and intensity. 0Hz is always at 3 o'clock. 22050 is always at 9 o'clock. The vertical line represents 11025Hz. Intensity is the distance from the center. The circle is called the unit circle and represents intensity=1. The IIR Z filter is a biquad filter. This means that there are two poles and two zeros. Both pairs are mirrored on the X axis, so only one of each shown on the display. The X and O controls have different effects depending on the type of filter selected. In highpass mode, both controls are active. In bandpass mode, the O control only effects frequency, it's distance from the center is irrelevant. In lowpass mode, the O control has no effect and is disabled. Logrithmic frequency scale warps the angular display to give more presicion at lower frequencies. The dots are one octave apart. Detail display mode will show the frequencies of the X and O in hertz. The dB display shows the approximate gain at the highest point on the responce curve. The responce curve is scaled so that the highest gain is closest to the edge. Responces with sharp peaks may not display accurately. This object clips it's signal at 1.0. Use the show clipping mode to display when this happens. Setting the pole close to the unit circle will result in oscillation.