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Attempted to introduce a lowpass filter to the graphics output, reverted 6502 optimisations as seemingly not working.

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Thomas Harte
2016-03-21 22:01:25 -04:00
parent 5db0f9e2d5
commit 3038704977
5 changed files with 166 additions and 151 deletions
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SignalProcessing/FIRFilter.cpp
+14 -5
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@@ -37,7 +37,7 @@ using namespace SignalProcessing;
#define kCSKaiserBesselFilterFixedShift 15
/* ino evaluates the 0th order Bessel function at a */
static float csfilter_ino(float a)
float FIRFilter::ino(float a)
{
float d = 0.0f;
float ds = 1.0f;
@@ -54,7 +54,8 @@ static float csfilter_ino(float a)
return s;
}
static void csfilter_setIdealisedFilterResponse(short *filterCoefficients, float *A, float attenuation, unsigned int numberOfTaps)
//static void csfilter_setIdealisedFilterResponse(short *filterCoefficients, float *A, float attenuation, unsigned int numberOfTaps)
void FIRFilter::coefficients_for_idealised_filter_response(short *filterCoefficients, float *A, float attenuation, unsigned int numberOfTaps)
{
/* calculate alpha, which is the Kaiser-Bessel window shape factor */
float a; // to take the place of alpha in the normal derivation
@@ -73,13 +74,13 @@ static void csfilter_setIdealisedFilterResponse(short *filterCoefficients, float
/* work out the right hand side of the filter coefficients */
unsigned int Np = (numberOfTaps - 1) / 2;
float I0 = csfilter_ino(a);
float I0 = ino(a);
float NpSquared = (float)(Np * Np);
for(unsigned int i = 0; i <= Np; i++)
{
filterCoefficientsFloat[Np + i] =
A[i] *
csfilter_ino(a * sqrtf(1.0f - ((float)(i * i) / NpSquared) )) /
ino(a * sqrtf(1.0f - ((float)(i * i) / NpSquared) )) /
I0;
}
@@ -106,6 +107,14 @@ static void csfilter_setIdealisedFilterResponse(short *filterCoefficients, float
delete[] filterCoefficientsFloat;
}
void FIRFilter::get_coefficients(float *coefficients)
{
for(unsigned int i = 0; i < number_of_taps_; i++)
{
coefficients[i] = (float)filter_coefficients_[i] / kCSKaiserBesselFilterFixedMultiplier;
}
}
FIRFilter::FIRFilter(unsigned int number_of_taps, unsigned int input_sample_rate, float low_frequency, float high_frequency, float attenuation)
{
// we must be asked to filter based on an odd number of
@@ -136,7 +145,7 @@ FIRFilter::FIRFilter(unsigned int number_of_taps, unsigned int input_sample_rate
) / iPi;
}
csfilter_setIdealisedFilterResponse(filter_coefficients_, A, attenuation, number_of_taps_);
FIRFilter::coefficients_for_idealised_filter_response(filter_coefficients_, A, attenuation, number_of_taps_);
/* clean up */
delete[] A;