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"""
===============
Resampling data
===============
When performing experiments where timing is critical, a signal with a high
sampling rate is desired. However, having a signal with a much higher sampling
rate than is necessary needlessly consumes memory and slows down computations
operating on the data.
This example downsamples from 600 Hz to 100 Hz. This achieves a 6-fold
reduction in data size, at the cost of an equal loss of temporal resolution.
"""
# Authors: Marijn van Vliet <w.m.vanvliet@gmail.com>
#
# License: BSD (3-clause)
from matplotlib import pyplot as plt
import mne
from mne.datasets import sample
###############################################################################
# Setting up data paths and loading raw data (skip some data for speed)
data_path = sample.data_path()
raw_fname = data_path + '/MEG/sample/sample_audvis_raw.fif'
raw = mne.io.read_raw_fif(raw_fname).crop(120, 240).load_data()
###############################################################################
# Since downsampling reduces the timing precision of events, we recommend
# first extracting epochs and downsampling the Epochs object:
events = mne.find_events(raw)
epochs = mne.Epochs(raw, events, event_id=2, tmin=-0.1, tmax=0.8, preload=True)
# Downsample to 100 Hz
print('Original sampling rate:', epochs.info['sfreq'], 'Hz')
epochs_resampled = epochs.copy().resample(100, npad='auto')
print('New sampling rate:', epochs_resampled.info['sfreq'], 'Hz')
# Plot a piece of data to see the effects of downsampling
plt.figure(figsize=(7, 3))
n_samples_to_plot = int(0.5 * epochs.info['sfreq']) # plot 0.5 seconds of data
plt.plot(epochs.times[:n_samples_to_plot],
epochs.get_data()[0, 0, :n_samples_to_plot], color='black')
n_samples_to_plot = int(0.5 * epochs_resampled.info['sfreq'])
plt.plot(epochs_resampled.times[:n_samples_to_plot],
epochs_resampled.get_data()[0, 0, :n_samples_to_plot],
'-o', color='red')
plt.xlabel('time (s)')
plt.legend(['original', 'downsampled'], loc='best')
plt.title('Effect of downsampling')
mne.viz.tight_layout()
###############################################################################
# When resampling epochs is unwanted or impossible, for example when the data
# doesn't fit into memory or your analysis pipeline doesn't involve epochs at
# all, the alternative approach is to resample the continuous data. This
# can only be done on loaded or pre-loaded data.
# Resample to 300 Hz
raw_resampled = raw.copy().resample(300, npad='auto')
###############################################################################
# Because resampling also affects the stim channels, some trigger onsets might
# be lost in this case. While MNE attempts to downsample the stim channels in
# an intelligent manner to avoid this, the recommended approach is to find
# events on the original data before downsampling.
print('Number of events before resampling:', len(mne.find_events(raw)))
# Resample to 100 Hz (suppress the warning that would be emitted)
raw_resampled = raw.copy().resample(100, npad='auto', verbose='error')
print('Number of events after resampling:',
len(mne.find_events(raw_resampled)))
# To avoid losing events, jointly resample the data and event matrix
events = mne.find_events(raw)
raw_resampled, events_resampled = raw.copy().resample(
100, npad='auto', events=events)
print('Number of events after resampling:', len(events_resampled))
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