Polyphase Filters (Delphi)

notes
Pascal conversion of C++ code by Dave from Muon Software. Conversion by Shannon Faulkner.
code
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{

polyphase filters, used for up and down-sampling
original c++ code by Dave from Muon Software found
at MusicDSP.
rewritten in pascal by Shannon Faulkner, 4/7/06.

}

unit uPolyphase;

interface

type
  TAllPass=class
  private
    a,x0,x1,x2,y0,y1,y2:single;
  public
    constructor create(coefficient:single);
    function Process(input:single):single;
  end;

  TAllPassFilterCascade=class
  private
    AllPassFilters:array of TAllPass;
    fOrder:integer;
  public
    constructor create(coefficients:psingle;Order:integer);
    function Process(input:single):single;
  end;

  THalfBandFilter=class
  private
    fOrder:integer;
    OldOut:single;
    aCoeffs,bCoeffs:array of single;
    FilterA,FilterB:TAllPassFilterCascade;
  public
    constructor create(order:integer;Steep:boolean);
    function process(input:single):single;
  end;


implementation
//-----------     AllPass Filter        -------------------
//-----------     AllPass Filter        ----------------------------------------------
//-----------     AllPass Filter        ----------------------------------------------
constructor TAllPass.create(coefficient:single);
begin
  a:=coefficient;

  x0:=0;
  x1:=0;
  x2:=0;

  y0:=0;
  y1:=0;
  y2:=0;
end;

function TAllPass.Process(input:single):single;
var output:single;
begin
  //shuffle inputs
  x2:=x1;
  x1:=x0;
  x0:=input;

  //shuffle outputs
  y2:=y1;
  y1:=y0;

  //allpass filter 1
  output:=x2+((input-y2)*a);

  y0:=output;

  result:=output;
end;
//------------     AllPass Filter Cascade     -------------
//------------     AllPass Filter Cascade     -------------
//------------     AllPass Filter Cascade     -------------
constructor TAllPassFilterCascade.create(coefficients:psingle;Order:integer);
var i:integer;
begin
  fOrder:=Order;
  setlength(AllPassFilters,fOrder);
  for i:=0 to fOrder-1 do
  begin
    AllPassFilters[i]:=TAllPass.create(coefficients^);
    inc(coefficients);
  end;
end;

function TAllPassFilterCascade.Process(input:single):single;
var
  output:single;
  i:integer;
begin
  output:=input;
  for i:=0 to fOrder-1 do
  begin
    output:=allpassfilters[i].Process(output);
  end;
  result:=output;
end;
//--------------   Halfband Filter    -------------------------------------------
//--------------   Halfband Filter    ---------------------
//--------------   Halfband Filter    -------------------------------------------
constructor THalfBandFilter.create(order:integer;Steep:boolean);
begin
  fOrder:=order;
  setlength(aCoeffs,Order div 2);
  setlength(bCoeffs,Order div 2);

  if steep=true then
  begin
    if (order=12) then //rejection=104dB, transition band=0.01
    begin
      aCoeffs[0]:=0.036681502163648017;
      aCoeffs[1]:=0.2746317593794541;
      aCoeffs[2]:=0.56109896978791948;
      aCoeffs[3]:=0.769741833862266;
      aCoeffs[4]:=0.8922608180038789;
      aCoeffs[5]:=0.962094548378084;

      bCoeffs[0]:=0.13654762463195771;
      bCoeffs[1]:=0.42313861743656667;
      bCoeffs[2]:=0.6775400499741616;
      bCoeffs[3]:=0.839889624849638;
      bCoeffs[4]:=0.9315419599631839;
      bCoeffs[5]:=0.9878163707328971;
    end
    else if (order=10) then //rejection=86dB, transition band=0.01
    begin
      aCoeffs[0]:=0.051457617441190984;
      aCoeffs[1]:=0.35978656070567017;
      aCoeffs[2]:=0.6725475931034693;
      aCoeffs[3]:=0.8590884928249939;
      aCoeffs[4]:=0.9540209867860787;

      bCoeffs[0]:=0.18621906251989334;
      bCoeffs[1]:=0.529951372847964;
      bCoeffs[2]:=0.7810257527489514;
      bCoeffs[3]:=0.9141815687605308;
      bCoeffs[4]:=0.985475023014907;
    end
    else if (order=8) then  //rejection=69dB, transition band=0.01
    begin
      aCoeffs[0]:=0.07711507983241622;
      aCoeffs[1]:=0.4820706250610472;
      aCoeffs[2]:=0.7968204713315797;
      aCoeffs[3]:=0.9412514277740471;

      bCoeffs[0]:=0.2659685265210946;
      bCoeffs[1]:=0.6651041532634957;
      bCoeffs[2]:=0.8841015085506159;
      bCoeffs[3]:=0.9820054141886075;
    end
    else if (order=6) then  //rejection=51dB, transition band=0.01
    begin
      aCoeffs[0]:=0.1271414136264853;
      aCoeffs[1]:=0.6528245886369117;
      aCoeffs[2]:=0.9176942834328115;

      bCoeffs[0]:=0.40056789819445626;
      bCoeffs[1]:=0.8204163891923343;
      bCoeffs[2]:=0.9763114515836773;
    end
    else if (order=4) then  //rejection=53dB,transition band=0.05
    begin
      aCoeffs[0]:=0.12073211751675449;
      aCoeffs[1]:=0.6632020224193995;

      bCoeffs[0]:=0.3903621872345006;
      bCoeffs[1]:=0.890786832653497;
    end
    else    //order=2, rejection=36dB, transition band=0.1
    begin
      aCoeffs[0]:=0.23647102099689224;
      bCoeffs[0]:=0.7145421497126001;
    end;
  end else  //softer slopes, more attenuation and less stopband ripple
  begin
    if (order=12) then //rejection=104dB, transition band=0.01
    begin
      aCoeffs[0]:=0.01677466677723562;
      aCoeffs[1]:=0.13902148819717805;
      aCoeffs[2]:=0.3325011117394731;
      aCoeffs[3]:=0.53766105314488;
      aCoeffs[4]:=0.7214184024215805;
      aCoeffs[5]:=0.8821858402078155;

      bCoeffs[0]:=0.06501319274445962;
      bCoeffs[1]:=0.23094129990840923;
      bCoeffs[2]:=0.4364942348420355;

      //bug fix - coefficient changed,
      //rob[DOT]belcham[AT]zen[DOT]co[DOT]uk
      //bCoeffs[3]:=0.06329609551399348;  //original coefficient
      bCoeffs[3]:=0.6329609551399348;     //correct coefficient

      bCoeffs[4]:=0.80378086794111226;
      bCoeffs[5]:=0.9599687404800694;
    end
    else if (order=10) then //rejection=86dB, transition band=0.01
    begin
      aCoeffs[0]:=0.02366831419883467;
      aCoeffs[1]:=0.18989476227180174;
      aCoeffs[2]:=0.43157318062118555;
      aCoeffs[3]:=0.6632020224193995;
      aCoeffs[4]:=0.860015542499582;

      bCoeffs[0]:=0.09056555904993387;
      bCoeffs[1]:=0.3078575723749043;
      bCoeffs[2]:=0.5516782402507934;
      bCoeffs[3]:=0.7652146863779808;
      bCoeffs[4]:=0.95247728378667541;
    end
    else if (order=8) then  //rejection=69dB, transition band=0.01
    begin
      aCoeffs[0]:=0.03583278843106211;
      aCoeffs[1]:=0.2720401433964576;
      aCoeffs[2]:=0.5720571972357003;
      aCoeffs[3]:=0.827124761997324;

      bCoeffs[0]:=0.1340901419430669;
      bCoeffs[1]:=0.4243248712718685;
      bCoeffs[2]:=0.7062921421386394;
      bCoeffs[3]:=0.9415030941737551;
    end
    else if (order=6) then  //rejection=51dB, transition band=0.01
    begin
      aCoeffs[0]:=0.06029739095712437;
      aCoeffs[1]:=0.4125907203610563;
      aCoeffs[2]:=0.7727156537429234;

      bCoeffs[0]:=0.21597144456092948;
      bCoeffs[1]:=0.6043586264658363;
      bCoeffs[2]:=0.9238861386532906;
    end
    else if (order=4) then  //rejection=53dB,transition band=0.05
    begin
      aCoeffs[0]:=0.07986642623635751;
      aCoeffs[1]:=0.5453536510711322;

      bCoeffs[0]:=0.28382934487410993;
      bCoeffs[1]:=0.8344118914807379;
    end
    else    //order=2, rejection=36dB, transition band=0.1
    begin
      aCoeffs[0]:=0.23647102099689224;
      bCoeffs[0]:=0.7145421497126001;
    end;
  end;

  FilterA:=TAllPassFilterCascade.create(@aCoeffs[0],fOrder div 2);
  FilterB:=TAllPassFilterCascade.create(@bCoeffs[0],fOrder div 2);

  oldout:=0;
end;

function THalfBandFilter.process(input:single):single;
begin
  result:=(FilterA.Process(input)+oldout)*0.5;
  oldout:=FilterB.Process(input);
end;

end.