Lowpass Filter
Overview
This is a recursive low-pass filter that supresses signal frequencies higher than the cut-off frequency for all channels at the input seperately.Operator ports
Input S: Floating point valuesOutput LP(S): Floating point values
Properties
Find more information about changing properties here: linkCutOffFrequency
type: See descriptionThe cut-off frequency in Hz (must be greater than 0)
TimeConstant
type: See descriptionThe time constant T of the filter in seconds.
Caption
type: Word or phraseThe name of the object in the project. This name must not contain '.' or '$' characters.
Every object has the Caption property. This property is very important, because it is the name by which Polybench recognizes this object.
It is allowed to give multiple objects the same name, as long as the objects are of the same type. In that case, a reference to this caption includes all the objects with the same caption.
In Polybench, every object can be addressed by an Address specifier, which starts with the dollar sign, for example: $My Page.My Object. 'My Page' would be the Caption of a page, and 'My Object' the Caption of an object on that page.
It is allowed to give multiple objects the same name, as long as the objects are of the same type. In that case, a reference to this caption includes all the objects with the same caption.
In Polybench, every object can be addressed by an Address specifier, which starts with the dollar sign, for example: $My Page.My Object. 'My Page' would be the Caption of a page, and 'My Object' the Caption of an object on that page.
Documentation
type: See descriptionOptional documentation of this object.
It is good practice to write in short notes why you have used this object, and why its properties are set the way they are set. If this object is an operator, the Documentation text is displayed below the operator symbol.
Variable Parameters
Find more information about Variable Parameters here: linkCutOffFrequency
type: See descriptionThe cut-off frequency in Hz (must be greater than 0)
TimeConstant
type: See descriptionThe time constant T of the filter in seconds.
Details
This filter uses the following formula to supress high frequencies:y(n) = k * y(n-1) + (1 - k) * x(n)
where k = e ^ ( -1 / ( Fs / (2 * PI * Fc) ) )
with:
Fs is the sample frequency,
PI is 3.1415...,
Fc is the cut-off frequency setting,
x(n) is the input sample value,
y(n) is the output sample value,
y(n-1) is the previous output sample value.
The time constant Tc and the cut-off frequency Fc have the following relation:
Fc = 1 / (2 * PI * Tc)
If the filter setting contains a wrong value (not a number or a wrong number), then the filter symbol will indicate this and will not output a valid signal anymore.
It is not allowed to connect a constant to the input of the filter (since a constant does not have a time component).
Examples
Example: Recursive Filter Demo
Demonstrates the High Pass and Low Pass standard filtersExamples\DF0204020_001_LowpassFilter_Demo.xmc