OnepoleUG Class Reference

OnepoleUG is a simple one-pole (recursive) filter, useful for low and high-pass filter. More...

#import <OnepoleUG.h>

List of all members.

Public Member Functions
(id)	- setInput:
	Sets the input patchpoint to aPatchPoint.
(id)	- setOutput:
	Sets the output patchpoint to aPatchPoint.
(id)	- setB0:
	Sets the filter's gain.
(id)	- setA1:
	Sets the filter's coefficient.
(id)	- clear
	Clears the filter by setting the delayed sample (the previous output sample) to 0.0.
(id)	- setState:
	Sets internal filter running term.
(id)	- setBrightness:forFreq:
	This is a convenient method that adjusts the filter's gain and coefficient such that a constant brightness value produces the same number and relative amplitudes of a tone's harmonics regardless of the value of frequency as described in Jaffe/Smith, Computer Music Journal Vol. 7, No. 2, Summer 1983.
Static Public Member Functions
(BOOL)	+ shouldOptimize:
	Specifies that all arguments are to be optimized if possible except the filter state.

---

Detailed Description

OnepoleUG is a simple one-pole (recursive) filter, useful for low and high-pass filter.

OnepoleUG is a one-pole filter that's implemented by subtracting the previous output sample (initialized as 0.0) from the current input sample:

output = (b0 * input) - (a1 * previousOutput)

previousOutput = output

Note that the two samples have their own scalers:

• b0, the filter's gain, scales the input sample. Effective gain values are between 0.0 and 1.0 (a negative gain is the same as its absolute value, but with a 180 degree phase shift).

• a1, the filter's coefficient, scales the previous output sample. If a1 is less than 0.0, the OnepoleUG is a low-pass filter; if it's greater than 0.0, the object is a high-pass filter. For stability, the value of a1 should be between -1.0 and 1.0 (non-inclusive).

Similar to the OnepoleUG is the OnezeroUG; it, too, is either a low-pass or a high-pass filter, but the frequency roll-off is gentler than with a OnepoleUG. You should also note that the high-pass/low-pass determination with regard to the sign of the coefficent is switched in the OnezeroUG.

Memory Spaces

OnepoleUGab a output b input

---

Member Function Documentation

- (id) setInput:

(id)

aPatchPoint

Sets the input patchpoint to aPatchPoint.

Parameters:

aPatchPoint

is an id.

Returns:

Returns an id. Returns nil if the argument isn't a patchpoint; otherwise returns self.

- (id) setOutput:

(id)

aPatchPoint

Sets the output patchpoint to aPatchPoint.

Parameters:

aPatchPoint

is an id.

Returns:

Returns an id. Returns nil if the argument isn't a patchpoint; otherwise returns self.

- (id) setB0:

(double)

value

Sets the filter's gain.

Parameters:

value

is a double.

Returns:

Returns self. Effective gain values are between 0.0 and 1.0 (a negative gain is the same as its absolute value, but with a 180 degree phase shift).

- (id) setA1:

(double)

value

Sets the filter's coefficient.

Parameters:

value

is a double.

Returns:

Returns self. If value is less than 0.0, the OnepoleUG is a low-pass filter; if it's greater than 0.0, the object is a high-pass filter. For stability, the value should be between -1.0 and 1.0.

+ (BOOL) shouldOptimize:

(unsigned)

arg

Specifies that all arguments are to be optimized if possible except the filter state.

Parameters:

arg

is an unsigned.

Returns:

Returns an BOOL.

- (id) clear

Clears the filter by setting the delayed sample (the previous output sample) to 0.0.

Returns:

Returns self.

- (id) setState:

(double)

val

Sets internal filter running term.

Parameters:

val

is a double.

Returns:

Returns an id.

- (id) setBrightness:		(double)	brightness
forFreq:		(double)	frequency

This is a convenient method that adjusts the filter's gain and coefficient such that a constant brightness value produces the same number and relative amplitudes of a tone's harmonics regardless of the value of frequency as described in Jaffe/Smith, Computer Music Journal Vol. 7, No. 2, Summer 1983.

For example, in a musical phrase during which the brightness of the synthesized notes shouldn't be perceived to change, you would invoke this method once per note passing a constant brightness value (the successive frequency values would, of course, be determined by the pitches of the notes).

Parameters:

	brightness	is a double specifying the gain.
	frequency	is a double.

Returns:

Returns self.

---

The documentation for this class was generated from the following file:

• OnepoleUG.h