/// <summary>
/// Apply FIR filter on signal
/// </summary>
/// <param name="filter">FIR filter object</param>
/// <param name="input">input signal</param>
/// <returns>array of floating-point samples of filtered signal</returns>
public static float[] ApplyFilter(this Filters.FIRFilter filter, float[] input)
{
float[] output = new float[input.Length];
unsafe
{
float *y = stackalloc float[input.Length];
libliquid.firfilt_apply(filter.Coefficients, filter.Coefficients.Length, input, input.Length, y);
for (int i = 0; i < output.Length; i++)
{
output[i] = y[i];
}
}
return(output);
}
/// <summary>
/// Design a Nyquist FIR filter
/// </summary>
/// <param name="type">filter type (e.g. kaiser, rrc etc.)</param>
/// <param name="_k">samples/symbol</param>
/// <param name="_m">symbol delay</param>
/// <param name="_beta">rolloff factor (0 < beta < 1)</param>
/// <param name="_dt">fractional sample delay</param>
/// <returns>returns FIR filter having co-efficient vector of length (2*_k*_m+1)</returns>
public static Filters.FIRFilter DesignFIR(FIR_Filter_Type type, int _k, int _m, float _beta, float _dt)
{
float[] h = new float[(2 * _k * _m + 1)];
unsafe
{
float *_h = stackalloc float[h.Length];
libliquid.liquid_firdes_prototype(type, _k, _m, _beta, _dt, _h);
for (int i = 0; i < h.Length; i++)
{
h[i] = _h[i];
}
}
Filters.FIRFilter f = new Filters.FIRFilter(h);
return(f);
}
/// <summary>
/// Designs a Kaiser FIR filter
/// </summary>
/// <param name="n">filter length</param>
/// <param name="fc">cut-off frequency</param>
/// <param name="As">Stopband attenuation</param>
/// <param name="mu">Fractional time delay</param>
/// <returns>FIRFilter object containing prototype co-efficients</returns>
public static Filters.FIRFilter DesignFIRKaiser(int n, float fc, float As, float mu, float _scale = 2)
{
float[] h = new float[n];
unsafe
{
float *_h = stackalloc float[n];
libliquid.liquid_firdes_kaiser(n, fc / _scale, As, mu, _h);
for (int i = 0; i < n; i++)
{
h[i] = _h[i];
}
}
Filters.FIRFilter f = new Filters.FIRFilter(h);
return(f);
}
