musicdsp.org source code archive - WSInf

This is done by generating a lowpass filter and then spectrally inverting it
procedure wsfirHP(var H : TDoubleArray; const WindowType : TWindowType; const CutOff : Double);
var i : Integer;
begin
wsfirLP(H, WindowType, CutOff); // 1. Generate lowpass filter
// 2. Spectrally invert (negate all samples and add 1 to center sample) lowpass filter
// = delta[n-((N-1)/2)] - h[n], in the time domain
for i:=0 to Length(H)-1
do H[i]:=H[i]*-1.0;
H[(Length(H)-1) div 2]:=H[(Length(H)-1) div 2]+1.0;
end;
// Generate bandstop filter
// This is done by generating a lowpass and highpass filter and adding them
procedure wsfirBS(var H : TDoubleArray; const WindowType : TWindowType; const LowCutOff, HighCutOff : Double);
var i : Integer;
H2 : TDoubleArray;
begin
SetLength(H2,Length(H));
// 1. Generate lowpass filter at first (low) cutoff frequency
wsfirLP(H, WindowType, LowCutOff);
// 2. Generate highpass filter at second (high) cutoff frequency
wsfirHP(H2, WindowType, HighCutOff);
// 3. Add the 2 filters together
for i:=0 to Length(H)-1
do H[i]:=H[i]+H2[i];
SetLength(H2,0);
end;
// Generate bandpass filter
// This is done by generating a bandstop filter and spectrally inverting it
procedure wsfirBP(var H : TDoubleArray; const WindowType : TWindowType; const LowCutOff, HighCutOff : Double);
var i : Integer;
begin
wsfirBS(H, WindowType, LowCutOff, HighCutOff); // 1. Generate bandstop filter
// 2. Spectrally invert (negate all samples and add 1 to center sample) lowpass filter
// = delta[n-((N-1)/2)] - h[n], in the time domain
for i:=0 to Length(H)-1
do H[i]:=H[i]*-1.0;
H[(Length(H)-1) div 2]:=H[(Length(H)-1) div 2]+1.0;
end;
// Generate sinc function - used for making lowpass filter
procedure genSinc(var Sinc : TDoubleArray; const Cutoff : Double);
var i,j : Integer;
n,k : Double;
begin
j:=Length(Sinc)-1;
k:=1/j;
// Generate sinc delayed by (N-1)/2
for i:=0 to j do
if (i=j div 2)
then Sinc[i]:=2.0*Cutoff
else
begin
n:=i-j/2.0;
Sinc[i]:=sin(2.0*PI*Cutoff*n)/(PI*n);
end;
end;
// Generate window function (Gaussian)
procedure wGaussian(var W : TDoubleArray);
var i,j : Integer;
k : Double;
begin
j:=Length(W)-1;
k:=1/j;
for i:=0 to j
do W[i]:=W[i]*(exp(-5.0/(sqr(j))*(2*i-j)*(2*i-j)));
end;
// Generate window function (Blackman-Harris)
procedure wBlackmanHarris(var W : TDoubleArray);
var i,j : Integer;
k : Double;
begin
j:=Length(W)-1;
k:=1/j;
for i:=0 to j