docs: def enforce_duration(self, duration_thresh):
          """
          This method takes a quantized pitch contour and filters out
          those time sections where the contour is not long enough, as specified
          by duration threshold (given in milliseconds).
  
          All transactions assume data in cent scale.
          """
          i = 1
          while i < len(self.pitch)-1:
              if self.pitch[i] == -10000:
                  i += 1
                  continue
              if self.pitch[i]-self.pitch[i-1] != 0 and self.pitch[i+1]-self.pitch[i] == 0:
                  start = i
                  while i < len(self.pitch) and self.pitch[i+1]-self.pitch[i] == 0:
                      i += 1
                  if (self.timestamps[i]-self.timestamps[start])*1000 < duration_thresh:
                      self.pitch[start:i+1] = np.zeros(i+1-start)-10000
              else:
                  self.pitch[i] = -10000
                  i += 1