code: def _iter_frequencies(self):
          
          # work out how many frequencies we need
          minf, maxf = self.frange
          fcum_mismatch = log(maxf / minf) * (2 + self.q**2)**(1/2.) / 2.
          nfreq = int(max(1, ceil(fcum_mismatch / self.deltam)))
          fstep = fcum_mismatch / nfreq
          fstepmin = 1 / self.duration
          # for each frequency, yield a QTile
          for i in xrange(nfreq):
              yield (minf *
                     exp(2 / (2 + self.q**2)**(1/2.) * (i + .5) * fstep) //
                     fstepmin * fstepmin)
docs: Iterate over the frequencies of this `QPlane`