/// <summary>
/// Calculates IIR.
/// </summary>
/// <param name="sample">sample rate</param>
/// <param name="pBiquad">BiquadCoefficients pointer</param>
public void BiQuad(ref Int16 sample, BiquadCoefficients *pBiquad)
{
// compute result
double result = pBiquad->a0 * sample + pBiquad->a1 * pBiquad->x1 +
pBiquad->a2 * pBiquad->x2 - pBiquad->a3 * pBiquad->y1 - pBiquad->a4 * pBiquad->y2;
// shift x1 to x2, sample to x1
pBiquad->x2 = pBiquad->x1;
pBiquad->x1 = sample;
// shift y1 to y2, result to y1
pBiquad->y2 = pBiquad->y1;
pBiquad->y1 = result;
sample = (Int16)result;
}
/// <summary>
/// Calculate amplitude change in BiquadCoefficients.
/// </summary>
private unsafe void _RecalculateBiquadBand(ref BiquadCoefficients *b, double dbGain, double frequency)
{
// reduce the gain thresholds on energetic signals to reduce distortion..
if (!Settings.isEightBitSample)
{
dbGain *= .1f;
}
BiquadCoefficients *tmp = Bands.BiQuadFilter(FiltersType.PEQ, dbGain, frequency, Settings.SamplesPerSecond, 1);
b->a0 = tmp->a0;
b->a1 = tmp->a1;
b->a2 = tmp->a2;
b->a3 = tmp->a3;
b->a4 = tmp->a4;
Bands.FreeMem(tmp);
tmp = null;
}
/// <summary>
///
/// </summary>
/// <param name="b"></param>
public void FreeMem(BiquadCoefficients *b)
{
Free(b);
}
/// <summary>Release heap memory</summary>
/// <param name="pmem">memory address</param>
private void Free(BiquadCoefficients *b)
{
HeapFree(GetProcessHeap(), 0, b);
}
private static extern bool HeapFree(IntPtr hHeap, uint dwFlags, BiquadCoefficients *lpMem);