Fold back distortion

• Author or source: ed.bpu@eriflleh
• Type: distortion
• Created: 2005-05-28 19:11:06

notes

a simple fold-back distortion filter.
if the signal exceeds the given threshold-level, it mirrors at the positive/negative
threshold-border as long as the singal lies in the legal range (-threshold..+threshold).
there is no range limit, so inputs doesn't need to be in -1..+1 scale.
threshold should be >0
depending on use (low thresholds) it makes sense to rescale the input to full amplitude

performs approximately the following code
(just without the loop)

while (in>threshold || in<-threshold)
{
  // mirror at positive threshold
  if (in>threshold) in= threshold - (in-threshold);
  // mirror at negative threshold
  if (in<-threshold) in= -threshold + (-threshold-in);
}

code

float foldback(float in, float threshold)
{
  if (in>threshold || in<-threshold)
  {
    in= fabs(fabs(fmod(in - threshold, threshold*4)) - threshold*2) - threshold;
  }
  return in;
}