Filter the annotation attributes to keep only items between the
        desired sample values

def apply_range(self, sampfrom=0, sampto=None):
        """
        Filter the annotation attributes to keep only items between the
        desired sample values

        """
        sampto = sampto or self.sample[-1]

        kept_inds = np.intersect1d(np.where(self.sample>=sampfrom),
                                   np.where(self.sample<=sampto))


        for field in ['sample', 'label_store', 'subtype', 'chan', 'num']:
            setattr(self, field, getattr(self, field)[kept_inds])

        self.aux_note = [self.aux_note[i] for i in kept_inds]

        self.ann_len = len(self.sample)