'Aux method.'

def _sources_as_raw(self, raw, add_channels, start, stop):

    sources = self._transform_raw(raw, start=start, stop=stop)
    if raw.preload:
        data = raw._data
        del raw._data
    out = raw.copy()
    if raw.preload:
        raw._data = data
    (start, stop) = _check_start_stop(raw, start, stop)
    if (add_channels is not None):
        raw_picked = raw.copy().pick_channels(add_channels)
        (data_, times_) = raw_picked[:, start:stop]
        data_ = np.r_[(sources, data_)]
    else:
        data_ = sources
        (_, times_) = raw[0, start:stop]
    out._data = data_
    out._times = times_
    out._filenames = [None]
    out.preload = True
    out._first_samps = np.array([(raw.first_samp + (start if start else 0))])
    out._last_samps = np.array([((out.first_samp + stop) if stop else raw.last_samp)])
    out._projector = None
    self._export_info(out.info, raw, add_channels)
    out._update_times()
    return out
