if len(lowpass) == 0:
    pass
elif len(set(lowpass)) == 1:
    if lowpass[0] in ('NaN', 'Off'):
        pass  # Placeholder for future use. Lowpass set in _empty_info
    else:
        info['lowpass'] = float(lowpass[0])
        if lp_s:
            # filter time constant t [secs] to Hz conversion: 1/2*pi*t
            info['lowpass'] = 1. / (2 * np.pi * info['lowpass'])

else:
    heterogeneous_lp_filter = True
    if lp_s:
        # We convert channels with disabled filters to having
        # infinitely relaxed / no filters
        lowpass = [float(filt) if filt not in ('NaN', 'Off')
                   else 0.0 for filt in lowpass]
        info['lowpass'] = np.min(np.array(lowpass, dtype=np.float64))
        try:
            # filter time constant t [secs] to Hz conversion: 1/2*pi*t
            info['lowpass'] = 1. / (2 * np.pi * info['lowpass'])

        except ZeroDivisionError:
            if len(set(lowpass)) == 1:
                # No lowpass actually set for the weakest setting
                # so we set lowpass to the Nyquist frequency
                info['lowpass'] = info['sfreq'] / 2.
                # not actually heterogeneous in effect
                # ... just heterogeneously disabled
                heterogeneous_lp_filter = False
            else:
                # no lowpass filter is the weakest filter,
                # but it wasn't the only filter
                pass
    else:
        # We convert channels with disabled filters to having
        # infinitely relaxed / no filters
        lowpass = [float(filt) if filt not in ('NaN', 'Off')
                   else np.Inf for filt in lowpass]
        info['lowpass'] = np.max(np.array(lowpass, dtype=np.float64))

        if np.isinf(info['lowpass']):
            # No lowpass actually set for the weakest setting
            # so we set lowpass to the Nyquist frequency
            info['lowpass'] = info['sfreq'] / 2.
            if len(set(lowpass)) == 1:
                # not actually heterogeneous in effect
                # ... just heterogeneously disabled
                heterogeneous_lp_filter = False

    if heterogeneous_lp_filter:
        # this isn't clean FP, but then again, we only want to provide
        # the Nyquist hint when the lowpass filter was actually
        # calculated from dividing the sampling frequency by 2, so the
        # exact/direct comparison (instead of tolerance) makes sense
        if info['lowpass'] == info['sfreq'] / 2.0:
            nyquist = ', Nyquist limit'
        else:
            nyquist = ""
        warn('Channels contain different lowpass filters. '
             'Highest (weakest) filter setting (%0.2f Hz%s) '
             'will be stored.' % (info['lowpass'], nyquist))