sds
August 10, 2022, 8:12pm
1
The frequency step in psd_welchpsd_multitaper
import mne
psds,freqs = mne.time_frequency.psd_multitaper(edf)
np.diff(freqs)
==> array([0.00164441, 0.00164441, 0.00164441, 0.00164441, 0.00164441, ...])
psds,freqs = mne.time_frequency.psd_welch(edf)
np.diff(freqs)
==> array([1.953125, 1.953125, 1.953125, 1.953125, 1.953125, 1.953125, ...])
Why? How do I control it?
mne.__version__ == '1.0.3'
PS. See also SO .
agramfort
August 10, 2022, 9:20pm
2
I assume that your edf variable is continuous data.
It’s the size of the FFT window that drives your frequency resolution.
If you want to increase the frequency resolution with welch increase the n_fft parameter
HTH
1 Like
sds
August 10, 2022, 9:36pm
3
Thank you!
What about decreasing resolution of psd_multitaper?really don’t need more than 0.3!
drammock
August 10, 2022, 9:46pm
4
I think for multitaper the only thing that affects freq bin spacing is number of samples and sampling frequency. See here:
so, I think no public API exists for doing a more sparse sampling of frequencies.
sds
August 10, 2022, 10:25pm
5
Thank you for the bad news ;-(
The code you are referencing is for psd_array_multitaper and it accepts sfreq that determines the sampling. However, I am interested in psd_multitaper, which gets sfreq from _check_psd_data which examines inst.info['sfreq'].
My EDF instance has inst.info['sfreq'] == 2000.0 and …
RuntimeError: sfreq cannot be set directly. Please use method inst.resample() instead.
I don’t see where this method is documented, but help seems to suggest
inst.resample(sfreq=???)
what do I pass there to reduce sampling?
drammock
August 10, 2022, 10:32pm
6
psd_multitaper calls psd_array_multitaper internally.
-----
.. versionadded:: 0.12.0
References
----------
.. footbibliography::
"""
# Prep data
data, sfreq = _check_psd_data(inst, tmin, tmax, picks, proj,
reject_by_annotation=reject_by_annotation)
return psd_array_multitaper(data, sfreq, fmin=fmin, fmax=fmax,
bandwidth=bandwidth, adaptive=adaptive,
low_bias=low_bias, normalization=normalization,
n_jobs=n_jobs, verbose=verbose)
inst.resample() in the error message means raw.resample() or epochs.resample() or evoked.resample() (inst means “instance”, i.e., an instance of one of those classes).
sds
August 10, 2022, 10:49pm
7
My edf.info["sfreq"] is 2000 and mne.time_frequency.psd_multitaper(edf) produces 1151033 frequencies with step 0.00086879 and range [0;1000].
After edf.resample(sfreq=100), I get 57552 frequencies with the same step(!) and smaller range [0;50].
This is certainly not what I want!