mne.filter.create_filter¶

mne.filter.
create_filter
(data, sfreq, l_freq, h_freq, filter_length='auto', l_trans_bandwidth='auto', h_trans_bandwidth='auto', method='fir', iir_params=None, phase='zero', fir_window='hamming', fir_design='firwin', verbose=None)[source]¶ Create a FIR or IIR filter.
l_freq
andh_freq
are the frequencies below which and above which, respectively, to filter out of the data. Thus the uses are:l_freq < h_freq
: bandpass filterl_freq > h_freq
: bandstop filterl_freq is not None and h_freq is None
: highpass filterl_freq is None and h_freq is not None
: lowpass filter
 Parameters
 data
ndarray
, shape (…, n_times) None
The data that will be filtered. This is used for sanity checking only. If None, no sanity checking related to the length of the signal relative to the filter order will be performed.
 sfreq
float
The sample frequency in Hz.
 l_freq
float
None
For FIR filters, the lower passband edge; for IIR filters, the lower cutoff frequency. If None the data are only lowpassed.
 h_freq
float
None
For FIR filters, the upper passband edge; for IIR filters, the upper cutoff frequency. If None the data are only highpassed.
 filter_length
str
int
Length of the FIR filter to use (if applicable):
‘auto’ (default): The filter length is chosen based on the size of the transition regions (6.6 times the reciprocal of the shortest transition band for fir_window=’hamming’ and fir_design=”firwin2”, and half that for “firwin”).
str: A humanreadable time in units of “s” or “ms” (e.g., “10s” or “5500ms”) will be converted to that number of samples if
phase="zero"
, or the shortest poweroftwo length at least that duration forphase="zerodouble"
.int: Specified length in samples. For fir_design=”firwin”, this should not be used.
 l_trans_bandwidth
float
str
Width of the transition band at the low cutoff frequency in Hz (high pass or cutoff 1 in bandpass). Can be “auto” (default) to use a multiple of
l_freq
:min(max(l_freq * 0.25, 2), l_freq)
Only used for
method='fir'
. h_trans_bandwidth
float
str
Width of the transition band at the high cutoff frequency in Hz (low pass or cutoff 2 in bandpass). Can be “auto” (default in 0.14) to use a multiple of
h_freq
:min(max(h_freq * 0.25, 2.), info['sfreq'] / 2.  h_freq)
Only used for
method='fir'
. method
str
‘fir’ will use overlapadd FIR filtering, ‘iir’ will use IIR forwardbackward filtering (via filtfilt).
 iir_params
dict
None
Dictionary of parameters to use for IIR filtering. If iir_params is None and method=”iir”, 4th order Butterworth will be used. For more information, see
mne.filter.construct_iir_filter()
. phase
str
Phase of the filter, only used if
method='fir'
. Symmetric linearphase FIR filters are constructed, and ifphase='zero'
(default), the delay of this filter is compensated for, making it noncausal. Ifphase=='zerodouble'
, then this filter is applied twice, once forward, and once backward (also making it noncausal). If ‘minimum’, then a minimumphase filter will be constricted and applied, which is causal but has weaker stopband suppression.New in version 0.13.
 fir_window
str
The window to use in FIR design, can be “hamming” (default), “hann” (default in 0.13), or “blackman”.
New in version 0.15.
 fir_design
str
Can be “firwin” (default) to use
scipy.signal.firwin()
, or “firwin2” to usescipy.signal.firwin2()
. “firwin” uses a timedomain design technique that generally gives improved attenuation using fewer samples than “firwin2”.New in version 0.15.
 verbosebool,
str
,int
, orNone
If not None, override default verbose level (see
mne.verbose()
and Logging documentation for more). If used, it should be passed as a keywordargument only.
 data
 Returns
See also
Notes
Note
For FIR filters, the cutoff frequency, i.e. the 6 dB point, is in the middle of the transition band (when using phase=’zero’ and fir_design=’firwin’). For IIR filters, the cutoff frequency is given by
l_freq
orh_freq
directly, andl_trans_bandwidth
andh_trans_bandwidth
are ignored.Bandpass filter
The frequency response is (approximately) given by:
1   /  \ H  /   \  /   \  /   \ 0          0 Fs1 Fp1 Fp2 Fs2 Nyq
Where:
Fs1 = Fp1  l_trans_bandwidth in Hz
Fs2 = Fp2 + h_trans_bandwidth in Hz
Bandstop filter
The frequency response is (approximately) given by:
1   \ / H  \ /  \ /  \ / 0        0 Fp1 Fs1 Fs2 Fp2 Nyq
Where
Fs1 = Fp1 + l_trans_bandwidth
andFs2 = Fp2  h_trans_bandwidth
.Multiple stop bands can be specified using arrays.
Lowpass filter
The frequency response is (approximately) given by:
1  \ H  \  \  \ 0      0 Fp Fstop Nyq
Where
Fstop = Fp + trans_bandwidth
.Highpass filter
The frequency response is (approximately) given by:
1   / H  /  /  / 0     0 Fstop Fp Nyq
Where
Fstop = Fp  trans_bandwidth
.New in version 0.14.