Stereo Enhancer

notes
Stereo Enhanca
code
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// WideCoeff  0.0 .... 1.5

#define StereoEnhanca(SamplL,SamplR,MonoSign, \
  DeltaLeft,WideCoeff ) \
  MonoSign = (SamplL + SamplR)/2.0; \
  DeltaLeft = SamplL - MonoSign; \
  DeltaLeft = DeltaLeft * WideCoeff; \
  SamplL=SamplL + DeltaLeft; \
  SamplR=SamplR - DeltaLeft;

Comments

#define StereoEnhanca(SamplL,SamplR,MonoSign,
  DeltaLeft,DeltaRight,WideCoeff )
  MonoSign = (SamplL + SamplR)/2.0;

  DeltaLeft = SamplL - MonoSign;
  DeltaLeft *= WideCoeff;
  DeltaRight = SamplR - MonoSign;
  DeltaRight *= WideCoeff;

  SamplL += DeltaLeft;
  SamplR += DeltaRight;

I think this is more along the lines of what you were trying to accomplish. I doubt this is
the correct way of implementing this type of thing however.

I believe both pieces of code do the same thing. Since MonoSign is set equal to the average
of the two signals, in the second case DeltaRight = -DeltaLeft.
  • Date: 2005-01-07 10:20:20
  • By: thaddy[@]thaddy.com
// Here's an implementation of the classic stereo enhancer in Delphi BASM
// Values below 0.1 have a narrowing effect
// Values abouve 0.1 widens
parameters:
Buffer = eax
Amount = edx
Samples = ecx

const
  Spread:single =  6.5536;

procedure Sound3d32f(Buffer:PSingle;Amount:Single;Samples:integer);
asm
  fld     Amount
  fmul    spread
  mov     ecx, edx       // move samples to ecx
  shr     ecx, 1         // divide by two, stereo = 2 samples
@Start:
  fld     [eax].dword    // left sample
  fld     [eax+4].dword  // right sample, whole calculation runs on the stack
  fld     st(0)          // copy
  fadd    st(0), st(2)
  fmul    half           // average =st(0), right sample = st(1), left = st(2), amount=st(3)
  fld     st(0)          // copy average
  fsubr   st(0), st(3)   // left diffence
  fmul    st(0), st(4)   // amount
  fadd    st(0), st(1)   // add average
  fadd    st(0), st(3)   // add original
  fmul    half           // divide by two
  fstp    [eax].dword    // and store
  fld     st(0)
  fsubr   st(0), st(2)   // right difference
  fmul    st(0), st(4)   // amount
  faddp                  // add average
  faddp                  // add original
  fmul    half           // divide by 2
  fstp    [eax+4].dword; // and store
  fxch                   // Dangling average?? remove it later, tdk
  ffree   st(1)
  add     eax, 8         // advance to next stereo pair
  loop    @Start
  ffree   st(0);         // Cleanup amount
end;

Note 'half' is defined as const half:single = 0.5;
This is an ommission in the above posting

This original code makes indeed no sense.

>#define StereoEnhanca(SamplL,SamplR,MonoSign, \
>DeltaLeft,WideCoeff ) \
>MonoSign = (SamplL + SamplR)/2.0; \
>DeltaLeft = SamplL - MonoSign; \
>DeltaLeft = DeltaLeft * WideCoeff; \
>SamplL=SamplL + DeltaLeft; \
>SamplR=SamplR - DeltaLeft;

Deltaleft hold no stereoinformation.
explained: Deltaleft=L-(L+R) = R!!!
So, in this example your stereo image would slide to the right more as you put widecoeff higher.

A better implementation is the following code.
#define StereoEnhanca(SamplL,SamplR,MonoSign, \
stereo,WideCoeff ) \
MonoSign = (SamplL + SamplR)/2.0; \
stereo = SamplL - Sampl1L; \
stereo = DeltaLeft * WideCoeff; \
SamplL=SamplR + stereo; // R+Stereo = L
SamplR=SamplL - stereo; // L-Stereo = R

This way of stereoenhancement will lead to exaggerated reverberation effects ( snaredrums).
This is not the best way to do widening, but it is the easiest.

Gtekprog.

Evert Verduin

oops,

stereo = SamplL - Sampl1L;
needs ofcourse to be
stereo = SamplL - Sampl1R;

and

stereo = DeltaLeft * WideCoeff; \
needs to be
stereo = stereo * WideCoeff; \

Again the correct code:

#define StereoEnhanca(SamplL,SamplR,MonoSign, \
stereo,WideCoeff ) \
MonoSign = (SamplL + SamplR)/2.0; \
stereo = SamplL - Sampl1R; \
stereo = stereo * WideCoeff; \
SamplL=SamplR + stereo; // R+Stereo = L
SamplR=SamplL - stereo; // L-Stereo = R

This will do.

Evert

You mean to use MonoSign variable somewhere - as in:

   #define StereoEnhanca(SamplL,SamplR,MonoSign, \
stereo,WideCoeff ) \
MonoSign = (SamplL + SamplR)/2.0; \
stereo = SamplL - Sampl1R; \
stereo = stereo * WideCoeff; \

SamplL = MonoSign + stereo; // R+Stereo = L
SamplR = MonoSign - stereo; // L-Stereo = R

Or some variation?

Clayton