c# - C#中的低通和高通滤波器

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Answer 1

LP and HP filter - Musicdsp.org documentation

我在我们的 sEMG 分析仪软件中用上面的半代码实现了过滤器，效果很好。

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]; }
    }
}

请注意，此过滤器是为音频 DSP 目的而创建的。要创建干净的输出，您需要将共振设置为 sqrt(2)。