filtro passa-basso e passa-alto in C#

Question

Ho bisogno di filtro passa-basso e passa-alto scritto in C#. Ho due array per questo processo di filtro. Penso che se provassi a convertire gli algoritmi di Matlab Butterworth e Chebyshev in C#, sarebbe più facile. Ma non sono riuscito a trovare il codice degli algoritmi butter.m e Chebyshev su Internet e non voglio installare strumenti matlab e signal processing nel mio computer. Potresti fornire quei codici per favore? Grazie ..

Answer 1

Dai un'occhiata a OpenCV/EmguCV.

Sono entrambi open source in modo da poter avere il "codice" se questo è quello che stai cercando.

Answer 2

ho trovato questo strumento online che sembra essere molto promettente: Interactive Digital Filter Design: Butterworth/Bessel/Chebyshev Filters

Basta inserire le vostre esigenze:

• disegno Filtro: Butterworth/Bessel/Chebyshev
• filtro passa-basso/passa-alto/passa-banda/Bandstop
• Ordine filtro
• Frequenze/frequenze d'angolo

Istruzioni presentare, e calcola le seguenti informazioni:

• Utili, poli, zeri
• relazione ricorrente
codice
• C attuare la relazione di ricorrenza
• Lotto di ampiezza, fase, impulso e step responses

È possibile implementare un filtro in C# direttamente dalla relazione di ricorrenza.

Se sono necessari solo alcuni filtri costanti, il gioco è fatto. Tuttavia, se è necessario essere in grado di regolare i parametri del filtro in fase di esecuzione, sarà necessario fare di più. Fortunatamente, il professore ha fornito the source code for his tool e dovrebbe essere possibile convertire in C#.

Answer 3

È possibile dare un'occhiata al codice sorgente per il filtro passa basso Butterworth here su un'altra domanda StackOverflow. Come altri sottolineano EmguCV viene fornito con un sacco di filtri codificati in modo efficiente e Disponibile fuori dalla scatola

Answer 4

Ecco l'intero funzioni di MATLAB online: http://sipi.usc.edu/manuals/matlab701/toolbox/signal/reftabl2.html#136613

Answer 5

http://www.musicdsp.org/archive.php?classid=3#38

ho implementato il filtro in semicode sopra come segue nel nostro software di analisi sEMG e funziona alla grande.

public class FilterButterworth 
{ 
    /// <summary> 
    /// rez amount, from sqrt(2) to ~ 0.1 
    /// </summary> 
    private readonly float resonance; 

    private readonly float frequency; 
    private readonly int sampleRate; 
    private readonly PassType passType; 

    private readonly float c, a1, a2, a3, b1, b2; 

    /// <summary> 
    /// Array of input values, latest are in front 
    /// </summary> 
    private float[] inputHistory = new float[2]; 

    /// <summary> 
    /// Array of output values, latest are in front 
    /// </summary> 
    private float[] outputHistory = new float[3]; 

    public FilterButterworth(float frequency, int sampleRate, PassType passType, float resonance) 
    { 
     this.resonance = resonance; 
     this.frequency = frequency; 
     this.sampleRate = sampleRate; 
     this.passType = passType; 

     switch (passType) 
     { 
      case PassType.Lowpass: 
       c = 1.0f/(float)Math.Tan(Math.PI * frequency/sampleRate); 
       a1 = 1.0f/(1.0f + resonance * c + c * c); 
       a2 = 2f * a1; 
       a3 = a1; 
       b1 = 2.0f * (1.0f - c * c) * a1; 
       b2 = (1.0f - resonance * c + c * c) * a1; 
       break; 
      case PassType.Highpass: 
       c = (float)Math.Tan(Math.PI * frequency/sampleRate); 
       a1 = 1.0f/(1.0f + resonance * c + c * c); 
       a2 = -2f * a1; 
       a3 = a1; 
       b1 = 2.0f * (c * c - 1.0f) * a1; 
       b2 = (1.0f - resonance * c + c * c) * a1; 
       break; 
     } 
    } 

    public enum PassType 
    { 
     Highpass, 
     Lowpass, 
    } 

    public void Update(float newInput) 
    { 
     float newOutput = a1 * newInput + a2 * this.inputHistory[0] + a3 * this.inputHistory[1] - b1 * this.outputHistory[0] - b2 * this.outputHistory[1]; 

     this.inputHistory[1] = this.inputHistory[0]; 
     this.inputHistory[0] = newInput; 

     this.outputHistory[2] = this.outputHistory[1]; 
     this.outputHistory[1] = this.outputHistory[0]; 
     this.outputHistory[0] = newOutput; 
    } 

    public float Value 
    { 
     get { return this.outputHistory[0]; } 
    } 
} 

Answer 6

Ecco alcuni esempi di codice C# di un filtro butterworth e chebyshev tramite FFT di NMath.

Answer 7

eccone uno che ha molte modalità, HP LP BP picco, e così via, è un filtro BiQuad forse a 2 poli statico qualcosa del genere, è un filtro particolare e ha un certo tipo di risultato digitale: https://github.com/filoe/cscore/blob/master/CSCore/DSP/BiQuad.cs

/* 
    * These implementations are based on http://www.earlevel.com/main/2011/01/02/biquad-formulas/ 
    */ 

    using System; 

    namespace CSCore.DSP 
    { 
     /// <summary> 
     /// Represents a biquad-filter. 
     /// </summary> 
     public abstract class BiQuad 
     { 
      /// <summary> 
      /// The a0 value. 
      /// </summary> 
      protected double A0; 
      /// <summary> 
      /// The a1 value. 
      /// </summary> 
      protected double A1; 
      /// <summary> 
      /// The a2 value. 
      /// </summary> 
      protected double A2; 
      /// <summary> 
      /// The b1 value. 
      /// </summary> 
      protected double B1; 
      /// <summary> 
      /// The b2 value. 
      /// </summary> 
      protected double B2; 
      /// <summary> 
      /// The q value. 
      /// </summary> 
      private double _q; 
      /// <summary> 
      /// The gain value in dB. 
      /// </summary> 
      private double _gainDB; 
      /// <summary> 
      /// The z1 value. 
      /// </summary> 
      protected double Z1; 
      /// <summary> 
      /// The z2 value. 
      /// </summary> 
      protected double Z2; 

      private double _frequency; 

      /// <summary> 
      /// Gets or sets the frequency. 
      /// </summary> 
      /// <exception cref="System.ArgumentOutOfRangeException">value;The samplerate has to be bigger than 2 * frequency.</exception> 
      public double Frequency 
      { 
       get { return _frequency; } 
       set 
       { 
        if (SampleRate < value * 2) 
        { 
         throw new ArgumentOutOfRangeException("value", "The samplerate has to be bigger than 2 * frequency."); 
        } 
        _frequency = value; 
        CalculateBiQuadCoefficients(); 
       } 
      } 

      /// <summary> 
      /// Gets the sample rate. 
      /// </summary> 
      public int SampleRate { get; private set; } 

      /// <summary> 
      /// The q value. 
      /// </summary> 
      public double Q 
      { 
       get { return _q; } 
       set 
       { 
        if (value <= 0) 
        { 
         throw new ArgumentOutOfRangeException("value"); 
        } 
        _q = value; 
        CalculateBiQuadCoefficients(); 
       } 
      } 

      /// <summary> 
      /// Gets or sets the gain value in dB. 
      /// </summary> 
      public double GainDB 
      { 
       get { return _gainDB; } 
       set 
       { 
        _gainDB = value; 
        CalculateBiQuadCoefficients(); 
       } 
      } 

      /// <summary> 
      /// Initializes a new instance of the <see cref="BiQuad"/> class. 
      /// </summary> 
      /// <param name="sampleRate">The sample rate.</param> 
      /// <param name="frequency">The frequency.</param> 
      /// <exception cref="System.ArgumentOutOfRangeException"> 
      /// sampleRate 
      /// or 
      /// frequency 
      /// or 
      /// q 
      /// </exception> 
      protected BiQuad(int sampleRate, double frequency) 
       : this(sampleRate, frequency, 1.0/Math.Sqrt(2)) 
      { 
      } 

      /// <summary> 
      /// Initializes a new instance of the <see cref="BiQuad"/> class. 
      /// </summary> 
      /// <param name="sampleRate">The sample rate.</param> 
      /// <param name="frequency">The frequency.</param> 
      /// <param name="q">The q.</param> 
      /// <exception cref="System.ArgumentOutOfRangeException"> 
      /// sampleRate 
      /// or 
      /// frequency 
      /// or 
      /// q 
      /// </exception> 
      protected BiQuad(int sampleRate, double frequency, double q) 
      { 
       if (sampleRate <= 0) 
        throw new ArgumentOutOfRangeException("sampleRate"); 
       if (frequency <= 0) 
        throw new ArgumentOutOfRangeException("frequency"); 
       if (q <= 0) 
        throw new ArgumentOutOfRangeException("q"); 
       SampleRate = sampleRate; 
       Frequency = frequency; 
       Q = q; 
       GainDB = 6; 
      } 

      /// <summary> 
      /// Processes a single <paramref name="input"/> sample and returns the result. 
      /// </summary> 
      /// <param name="input">The input sample to process.</param> 
      /// <returns>The result of the processed <paramref name="input"/> sample.</returns> 
      public float Process(float input) 
      { 
       double o = input * A0 + Z1; 
       Z1 = input * A1 + Z2 - B1 * o; 
       Z2 = input * A2 - B2 * o; 
       return (float)o; 
      } 

      /// <summary> 
      /// Processes multiple <paramref name="input"/> samples. 
      /// </summary> 
      /// <param name="input">The input samples to process.</param> 
      /// <remarks>The result of the calculation gets stored within the <paramref name="input"/> array.</remarks> 
      public void Process(float[] input) 
      { 
       for (int i = 0; i < input.Length; i++) 
       { 
        input[i] = Process(input[i]); 
       } 
      } 

      /// <summary> 
      /// Calculates all coefficients. 
      /// </summary> 
      protected abstract void CalculateBiQuadCoefficients(); 
     } 

     /// <summary> 
     /// Used to apply a lowpass-filter to a signal. 
     /// </summary> 
     public class LowpassFilter : BiQuad 
     { 
      /// <summary> 
      /// Initializes a new instance of the <see cref="LowpassFilter"/> class. 
      /// </summary> 
      /// <param name="sampleRate">The sample rate.</param> 
      /// <param name="frequency">The filter's corner frequency.</param> 
      public LowpassFilter(int sampleRate, double frequency) 
       : base(sampleRate, frequency) 
      { 
      } 

      /// <summary> 
      /// Calculates all coefficients. 
      /// </summary> 
      protected override void CalculateBiQuadCoefficients() 
      { 
       double k = Math.Tan(Math.PI * Frequency/SampleRate); 
       var norm = 1/(1 + k/Q + k * k); 
       A0 = k * k * norm; 
       A1 = 2 * A0; 
       A2 = A0; 
       B1 = 2 * (k * k - 1) * norm; 
       B2 = (1 - k/Q + k * k) * norm; 
      } 
     } 

     /// <summary> 
     /// Used to apply a highpass-filter to a signal. 
     /// </summary> 
     public class HighpassFilter : BiQuad 
     { 
      private int p1; 
      private double p2; 

      /// <summary> 
      /// Initializes a new instance of the <see cref="HighpassFilter"/> class. 
      /// </summary> 
      /// <param name="sampleRate">The sample rate.</param> 
      /// <param name="frequency">The filter's corner frequency.</param> 
      public HighpassFilter(int sampleRate, double frequency) 
       : base(sampleRate, frequency) 
      { 
      } 

      /// <summary> 
      /// Calculates all coefficients. 
      /// </summary> 
      protected override void CalculateBiQuadCoefficients() 
      { 
       double k = Math.Tan(Math.PI * Frequency/SampleRate); 
       var norm = 1/(1 + k/Q + k * k); 
       A0 = 1 * norm; 
       A1 = -2 * A0; 
       A2 = A0; 
       B1 = 2 * (k * k - 1) * norm; 
       B2 = (1 - k/Q + k * k) * norm; 
      } 
     } 

     /// <summary> 
     /// Used to apply a bandpass-filter to a signal. 
     /// </summary> 
     public class BandpassFilter : BiQuad 
     { 
      /// <summary> 
      /// Initializes a new instance of the <see cref="BandpassFilter"/> class. 
      /// </summary> 
      /// <param name="sampleRate">The sample rate.</param> 
      /// <param name="frequency">The filter's corner frequency.</param> 
      public BandpassFilter(int sampleRate, double frequency) 
       : base(sampleRate, frequency) 
      { 
      } 

      /// <summary> 
      /// Calculates all coefficients. 
      /// </summary> 
      protected override void CalculateBiQuadCoefficients() 
      { 
       double k = Math.Tan(Math.PI * Frequency/SampleRate); 
       double norm = 1/(1 + k/Q + k * k); 
       A0 = k/Q * norm; 
       A1 = 0; 
       A2 = -A0; 
       B1 = 2 * (k * k - 1) * norm; 
       B2 = (1 - k/Q + k * k) * norm; 
      } 
     } 

     /// <summary> 
     /// Used to apply a notch-filter to a signal. 
     /// </summary> 
     public class NotchFilter : BiQuad 
     { 
      /// <summary> 
      /// Initializes a new instance of the <see cref="NotchFilter"/> class. 
      /// </summary> 
      /// <param name="sampleRate">The sample rate.</param> 
      /// <param name="frequency">The filter's corner frequency.</param> 
      public NotchFilter(int sampleRate, double frequency) 
       : base(sampleRate, frequency) 
      { 
      } 

      /// <summary> 
      /// Calculates all coefficients. 
      /// </summary> 
      protected override void CalculateBiQuadCoefficients() 
      { 
       double k = Math.Tan(Math.PI * Frequency/SampleRate); 
       double norm = 1/(1 + k/Q + k * k); 
       A0 = (1 + k * k) * norm; 
       A1 = 2 * (k * k - 1) * norm; 
       A2 = A0; 
       B1 = A1; 
       B2 = (1 - k/Q + k * k) * norm; 
      } 
     } 

     /// <summary> 
     /// Used to apply a lowshelf-filter to a signal. 
     /// </summary> 
     public class LowShelfFilter : BiQuad 
     { 
      /// <summary> 
      /// Initializes a new instance of the <see cref="LowShelfFilter"/> class. 
      /// </summary> 
      /// <param name="sampleRate">The sample rate.</param> 
      /// <param name="frequency">The filter's corner frequency.</param> 
      /// <param name="gainDB">Gain value in dB.</param> 
      public LowShelfFilter(int sampleRate, double frequency, double gainDB) 
       : base(sampleRate, frequency) 
      { 
       GainDB = gainDB; 
      } 

      /// <summary> 
      /// Calculates all coefficients. 
      /// </summary> 
      protected override void CalculateBiQuadCoefficients() 
      { 
       const double sqrt2 = 1.4142135623730951; 
       double k = Math.Tan(Math.PI * Frequency/SampleRate); 
       double v = Math.Pow(10, Math.Abs(GainDB)/20.0); 
       double norm; 
       if (GainDB >= 0) 
       { // boost 
        norm = 1/(1 + sqrt2 * k + k * k); 
        A0 = (1 + Math.Sqrt(2 * v) * k + v * k * k) * norm; 
        A1 = 2 * (v * k * k - 1) * norm; 
        A2 = (1 - Math.Sqrt(2 * v) * k + v * k * k) * norm; 
        B1 = 2 * (k * k - 1) * norm; 
        B2 = (1 - sqrt2 * k + k * k) * norm; 
       } 
       else 
       { // cut 
        norm = 1/(1 + Math.Sqrt(2 * v) * k + v * k * k); 
        A0 = (1 + sqrt2 * k + k * k) * norm; 
        A1 = 2 * (k * k - 1) * norm; 
        A2 = (1 - sqrt2 * k + k * k) * norm; 
        B1 = 2 * (v * k * k - 1) * norm; 
        B2 = (1 - Math.Sqrt(2 * v) * k + v * k * k) * norm; 
       } 
      } 
     } 

     /// <summary> 
     /// Used to apply a highshelf-filter to a signal. 
     /// </summary> 
     public class HighShelfFilter : BiQuad 
     { 
      /// <summary> 
      /// Initializes a new instance of the <see cref="HighShelfFilter"/> class. 
      /// </summary> 
      /// <param name="sampleRate">The sample rate.</param> 
      /// <param name="frequency">The filter's corner frequency.</param> 
      /// <param name="gainDB">Gain value in dB.</param> 
      public HighShelfFilter(int sampleRate, double frequency, double gainDB) 
       : base(sampleRate, frequency) 
      { 
       GainDB = gainDB; 
      } 

      /// <summary> 
      /// Calculates all coefficients. 
      /// </summary> 
      protected override void CalculateBiQuadCoefficients() 
      { 
       const double sqrt2 = 1.4142135623730951; 
       double k = Math.Tan(Math.PI * Frequency/SampleRate); 
       double v = Math.Pow(10, Math.Abs(GainDB)/20.0); 
       double norm; 
       if (GainDB >= 0) 
       { // boost 
        norm = 1/(1 + sqrt2 * k + k * k); 
        A0 = (v + Math.Sqrt(2 * v) * k + k * k) * norm; 
        A1 = 2 * (k * k - v) * norm; 
        A2 = (v - Math.Sqrt(2 * v) * k + k * k) * norm; 
        B1 = 2 * (k * k - 1) * norm; 
        B2 = (1 - sqrt2 * k + k * k) * norm; 
       } 
       else 
       { // cut 
        norm = 1/(v + Math.Sqrt(2 * v) * k + k * k); 
        A0 = (1 + sqrt2 * k + k * k) * norm; 
        A1 = 2 * (k * k - 1) * norm; 
        A2 = (1 - sqrt2 * k + k * k) * norm; 
        B1 = 2 * (k * k - v) * norm; 
        B2 = (v - Math.Sqrt(2 * v) * k + k * k) * norm; 
       } 
      } 
     } 

     /// <summary> 
     /// Used to apply an peak-filter to a signal. 
     /// </summary> 
     public class PeakFilter : BiQuad 
     { 
      /// <summary> 
      /// Gets or sets the bandwidth. 
      /// </summary> 
      public double BandWidth 
      { 
       get { return Q; } 
       set 
       { 
        if (value <= 0) 
         throw new ArgumentOutOfRangeException("value"); 
        Q = value; 
       } 
      } 

      /// <summary> 
      /// Initializes a new instance of the <see cref="PeakFilter"/> class. 
      /// </summary> 
      /// <param name="sampleRate">The sampleRate of the audio data to process.</param> 
      /// <param name="frequency">The center frequency to adjust.</param> 
      /// <param name="bandWidth">The bandWidth.</param> 
      /// <param name="peakGainDB">The gain value in dB.</param> 
      public PeakFilter(int sampleRate, double frequency, double bandWidth, double peakGainDB) 
       : base(sampleRate, frequency, bandWidth) 
      { 
       GainDB = peakGainDB; 
      } 

      /// <summary> 
      /// Calculates all coefficients. 
      /// </summary> 
      protected override void CalculateBiQuadCoefficients() 
      { 
       double norm; 
       double v = Math.Pow(10, Math.Abs(GainDB)/20.0); 
       double k = Math.Tan(Math.PI * Frequency/SampleRate); 
       double q = Q; 

       if (GainDB >= 0) //boost 
       { 
        norm = 1/(1 + 1/q * k + k * k); 
        A0 = (1 + v/q * k + k * k) * norm; 
        A1 = 2 * (k * k - 1) * norm; 
        A2 = (1 - v/q * k + k * k) * norm; 
        B1 = A1; 
        B2 = (1 - 1/q * k + k * k) * norm; 
       } 
       else //cut 
       { 
        norm = 1/(1 + v/q * k + k * k); 
        A0 = (1 + 1/q * k + k * k) * norm; 
        A1 = 2 * (k * k - 1) * norm; 
        A2 = (1 - 1/q * k + k * k) * norm; 
        B1 = A1; 
        B2 = (1 - v/q * k + k * k) * norm; 
       } 
      } 
     } 
    }