def normalize(self, mag=1.):
        """Normalize a Channel, set `null` to 0 and the mag to given value.

        Parameters
        ----------
        mag : float (optional)
            New value of mag. Default is 1.
        """

        def f(dataset, s, null, mag):
            dataset[s] -= null
            dataset[s] /= mag

        if self.signed:
            mag = self.mag() / mag
        else:
            mag = self.max() / mag
        self.chunkwise(f, null=self.null, mag=mag)
        self._null = 0