summaryrefslogtreecommitdiff
path: root/libs/ardour/dsp_filter.cc
diff options
context:
space:
mode:
authorRobin Gareus <robin@gareus.org>2016-05-20 23:14:51 +0200
committerRobin Gareus <robin@gareus.org>2016-05-20 23:14:51 +0200
commitd7e590f9c88ed5ca0b862dda146ff58ef4e1d842 (patch)
treea4f2f6b97552a647df85f26e8b4c8afa6d2f1ef6 /libs/ardour/dsp_filter.cc
parent125e2014aafbb0362725f780470f5654b66b53ce (diff)
add lua DSP transfer function calculation
Diffstat (limited to 'libs/ardour/dsp_filter.cc')
-rw-r--r--libs/ardour/dsp_filter.cc31
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)));
+}