winamp/Src/Plugins/DSP/dsp_sps/general.bin

SPS allows you to program signal processing using simple expressions.

Many aspects of SPS code are similar to C (including comments).

You can create new variables just by using them, and you can read
and write predefined variables (of which each effect has its own)
to interact with the effect. Note that variables are all floating
point numbers (no strings), and the maximum length of a variable's
name is 8 characters (anything longer will be ignored).

So, to create a variable, you can simply use it, for example:
  x = 5;

You can also use a variety of operators and math functions to
modify variables, see the Operators and Functions tabs above.

Code can include C and C++ style comments:
  // using the doubleslash comments until the end of the line
  /* using the classic C comments
     comment a block of text */

You can combine operators and functions into expressions, such
as:
  x = 5 * cos(y) / 32.0; // this does some leetness right here

You can use multiple expressions by seperating them with one or
more semicolons, for example:
  x = x * 17.0; x = x / 5; y = pow(x,3.0);

It is worth noting that extra whitespace (spaces, newlines) is
ignored, so if you need to space things out for clarity, you can.

Variables that are predefined for your effect to use:
  nch:  number of channels of PCM stream (1 or 2)
  srate: samplerate of stream (i.e. 44100)
  slider1, slider2, slider3, slider4: the four sliders. Each has a range of 0.0..1.0
  trig1, trig2, trig3, trig4: the four trigger buttons. These should be reset to 0.0
  by your code when you've caught the trigger

Variables that your per-sample code can modify to apply its effect:
  spl0 = left/mono channel sample, -1.0..1.0
  spl1 = right channel sample, if nch == 2, -1.0..1.0
  skip = set this to > 0 to drop the current sample and not output it
         (this effectively can be used to speed up the output
  repeat = set this to > 0 to process this sample again after
           outputting (this effectively can be used to slow down
           the output. Note that the most you can slow down the
           output due to Winamp architecture limitations is by 50%)

Now to the important part, how to actually make meaningful effects:
  A simple volume control might be:
    spl0 = spl0*slider1; spl1=spl1*slider1;
  To slow down the output to half speed:
    tmp=bnot(tmp); repeat=tmp;
  To speed up the output to double speed:
    tmp=bnot(tmp); skip=tmp;
  To swap left and right channels:
    tmp=spl0; spl0=spl1; spl1=tmp;
  etc�