generator that yields a *Signal* for each non-master channel

        Parameters
        ----------
        skip_master : bool
            do not yield master channels; default *True*
        copy_master : bool
            copy master for each yielded channel

def iter_channels(self, skip_master=True, copy_master=True):
        """ generator that yields a *Signal* for each non-master channel

        Parameters
        ----------
        skip_master : bool
            do not yield master channels; default *True*
        copy_master : bool
            copy master for each yielded channel

        """

        for i, group in enumerate(self.groups):

            included_channels = self._included_channels(i, skip_master=skip_master)

            channels = [
                (None, i, idx)
                for idx in included_channels
            ]

            channels = self.select(
                channels,
                copy_master=copy_master,
            )

            for channel in channels:
                yield channel