diff options
Diffstat (limited to 'libs/ardour/dsp_filter.cc')
-rw-r--r-- | libs/ardour/dsp_filter.cc | 31 |
1 files changed, 28 insertions, 3 deletions
diff --git a/libs/ardour/dsp_filter.cc b/libs/ardour/dsp_filter.cc index 2678d0008c..f82b5e46cf 100644 --- a/libs/ardour/dsp_filter.cc +++ b/libs/ardour/dsp_filter.cc @@ -145,14 +145,18 @@ BiQuad::run (float *data, const uint32_t n_samples) void BiQuad::compute (Type type, double freq, double Q, double gain) { + if (Q <= .001) { Q = 0.001; } + if (freq <= 1.) { freq = 1.; } + if (freq >= _rate) { freq = _rate; } + /* Compute biquad filter settings. * Based on 'Cookbook formulae for audio EQ biquad filter coefficents' * by Robert Bristow-Johnson */ - const double A = pow (10.0, (gain / 40.0)); + const double A = pow (10.0, (gain / 40.0)); const double W0 = (2.0 * M_PI * freq) / _rate; - const double sinW0 = sin (W0); - const double cosW0 = cos (W0); + const double sinW0 = sin (W0); + const double cosW0 = cos (W0); const double alpha = sinW0 / (2.0 * Q); const double beta = sqrt (A) / Q; @@ -250,3 +254,24 @@ BiQuad::compute (Type type, double freq, double Q, double gain) _a1 /= _a0; _a2 /= _a0; } + +float +BiQuad::dB_at_freq (float freq) const +{ + const double W0 = (2.0 * M_PI * freq) / _rate; + const float c1 = cosf (W0); + const float s1 = sinf (W0); + + const float A = _b0 + _b2; + const float B = _b0 - _b2; + const float C = 1.0 + _a2; + const float D = 1.0 - _a2; + + const float a = A * c1 + _b1; + const float b = B * s1; + const float c = C * c1 + _a1; + const float d = D * s1; + +#define SQUARE(x) ( (x) * (x) ) + return 20.f * log10f (sqrtf ((SQUARE(a) + SQUARE(b)) * (SQUARE(c) + SQUARE(d))) / (SQUARE(c) + SQUARE(d))); +} |