'Baseline correct epochs.
Parameters
baseline : tuple of length 2
The time interval to apply baseline correction. If None do not
apply it. If baseline is (a, b) the interval is between "a (s)" and
"b (s)". If a is None the beginning of the data is used and if b is
None then b is set to the end of the interval. If baseline is equal
to (None, None) all the time interval is used. Correction is
applied by computing mean of the baseline period and subtracting it
from the data. The baseline (a, b) includes both endpoints, i.e.
all timepoints t such that a <= t <= b.
verbose : bool, str, int, or None
If not None, override default verbose level (see
:func:`mne.verbose` and :ref:`Logging documentation <tut_logging>`
for more).
Returns
epochs : instance of Epochs
The baseline-corrected Epochs object.
Notes
Baseline correction can be done multiple times.
.. versionadded:: 0.10.0'

@verbose
def apply_baseline(self, baseline=(None, 0), verbose=None):

    if (not self.preload):
        raise RuntimeError('Data    must    be    loaded    to    apply    a    new    baseline')
    _check_baseline(baseline, self.tmin, self.tmax, self.info['sfreq'])
    picks = _pick_data_channels(self.info, exclude=[], with_ref_meg=True)
    picks_aux = _pick_aux_channels(self.info, exclude=[])
    picks = np.sort(np.concatenate((picks, picks_aux)))
    data = self._data
    data[:, picks, :] = rescale(data[:, picks, :], self.times, baseline, copy=False)
    self.baseline = baseline
    return self
