code: def denoise(self,bitthresh=0.5):
          
          for i in range(self.width):
              tot = 0
              for letter in ACGT:
                  if self.logP:
                      Pij = pow(2.0, self.logP[i][letter])
                  else:
                      Pij = pow(2.0, self.ll[i][letter]) * self.background[letter]
                  if Pij > 0.01:
                      bit = Pij * self.ll[i][letter]
                      tot = tot + bit
              if tot < bitthresh:  #Zero Column
                  for letter in ACGT:
                      self.ll[i][letter] = 0.0
          self.compute_from_ll(self.ll)
docs: m.denoise(bitthresh=0.5) -- Set low-information positions (below bitthresh) to Ns