NewGamePhysics.Physics.ButterworthFilter Class Reference

Implementation of a numerical biquad (tweaked) Butterworth filter. More...

List of all members.

Public Member Functions

 ButterworthFilter (ButterworthFilterType filterType, double sampleRate, double cutoffFrequency)
 Create an instance of a biquad Butterworth filter.
 ButterworthFilter (ButterworthFilterType filterType, double sampleRate, double cutoffFrequency, double resonance)
 Create an instance of a biquad Butterworth filter.
double[] Calculate (double[] samples)
 Calculate the filtered samples from the input samples.

Static Public Attributes

static double DefaultResonance = Math.Sqrt(2.0)
 Square root of 2.

Detailed Description

Implementation of a numerical biquad (tweaked) Butterworth filter.

Source: http://www.musicdsp.org/archive.php?classid=3#38 and Source: http://www.musicdsp.org/archive.php?classid=3#128 and Source: http://en.wikipedia.org/wiki/Digital_biquad_filter

Definition at line 37 of file ButterworthFilter.cs.

Constructor & Destructor Documentation

NewGamePhysics.Physics.ButterworthFilter.ButterworthFilter ( ButterworthFilterType  filterType,
double  sampleRate,
double  cutoffFrequency 
)

Create an instance of a biquad Butterworth filter.

Parameters:
filterType The type of the filter.
sampleRate The sample rate (Hz) to assume.
cutoffFrequency The cutoff frequency (Hz). Theoretical value 0 Hz to SampleRate/2, but practical is only SampleRate/4.

Uses default resonance of sqrt(2).

Definition at line 85 of file ButterworthFilter.cs.

00088                                     : this(filterType, sampleRate, cutoffFrequency, DefaultResonance) 
00089         {
00090         }

NewGamePhysics.Physics.ButterworthFilter.ButterworthFilter ( ButterworthFilterType  filterType,
double  sampleRate,
double  cutoffFrequency,
double  resonance 
)

Create an instance of a biquad Butterworth filter.

Parameters:
filterType The type of the filter.
sampleRate The sample rate (Hz) to assume.
cutoffFrequency The cutoff frequency (Hz). Theoretical value 0 Hz to SampleRate/2, but practical is only SampleRate/4.
resonance A resonance amount. Allowable range is from sqrt(2) to 0.1 only. At sqrt(2) resonance is 0dB, smaller values increase resonance.

Definition at line 109 of file ButterworthFilter.cs.

00114         {
00115             // Check input parameters
00116             if (sampleRate <= 0.0)
00117             {
00118                 throw new ArgumentException("The sample rate cannot be zero or negative.");
00119             }
00120 
00121             if ((cutoffFrequency <= 0.0) || 
00122                 (cutoffFrequency > (sampleRate / 2.0)))
00123             {
00124                 throw new ArgumentException("The cutoff frequency should be greater than " +
00125                     "zero, but less than half the sample rate");
00126             }
00127 
00128             if ((resonance < 0.1) || (resonance > DefaultResonance))
00129             {
00130                 throw new ArgumentException("The resonance parameter should be in " +
00131                     " the range 0.1 to sqrt(2)");
00132             }
00133 
00134             // Calculate filter parameters
00135             switch (filterType)
00136             {
00137                 case ButterworthFilterType.LowPass:
00138                     this.InitializeLowPass(sampleRate, cutoffFrequency, resonance);
00139                     break;
00140                 case ButterworthFilterType.HighPass:
00141                     this.InitializeHighPass(sampleRate, cutoffFrequency, resonance);
00142                     break;
00143             }
00144         }

Member Function Documentation

double [] NewGamePhysics.Physics.ButterworthFilter.Calculate ( double[]  samples  ) 

Calculate the filtered samples from the input samples.

Parameters:
samples Sample array. Minimum size of array is 3 samples.
Returns:
Filtered sample array. First two samples are 0.0.

Definition at line 192 of file ButterworthFilter.cs.

00194         {
00195             if (samples == null)
00196             {
00197                 throw new ArgumentNullException("samples");
00198             }
00199 
00200             int nMax = samples.Length;
00201             if (nMax < 3)
00202             {
00203                 throw new ArgumentException(
00204                     "samples", 
00205                     "The samples array must contain at least 3 values.");
00206             }
00207 
00208             double[] filteredSamples = new double[nMax];
00209             filteredSamples[0] = 0.0;
00210             filteredSamples[1] = 0.0;
00211             for (int n = 2; n < nMax; n++)
00212             {
00213                 filteredSamples[n] =
00214                     this.a1 * samples[n] +
00215                     this.a2 * samples[n - 1] +
00216                     this.a3 * samples[n - 2] -
00217                     this.b1 * filteredSamples[n - 1] -
00218                     this.b2 * filteredSamples[n - 2];
00219             }
00220 
00221             return filteredSamples;
00222         }

Member Data Documentation

double NewGamePhysics.Physics.ButterworthFilter.DefaultResonance = Math.Sqrt(2.0) [static]

Square root of 2.

Definition at line 42 of file ButterworthFilter.cs.

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