def compute_spectrum_medfilt(sig, fs, filt_len=1., f_range=None):
"""Estimate the power spectral densitry as a smoothed FFT.
Parameters
----------
sig : 1d or 2d array
Time series of measurement values.
fs : float
Sampling rate, in Hz.
filt_len : float, optional, default: 1.
Length of the median filter, in Hz.
f_range : list of [float, float] optional
Frequency range to sub-select from the power spectrum.
Returns
-------
freqs : 1d array
Array of sample frequencies.
spectrum : 1d or 2d array
Power spectral density.
"""
# Take the positive half of the spectrum since it's symmetrical
ft = np.fft.fft(sig)[:int(np.ceil(len(sig) / 2.))]
freqs = np.fft.fftfreq(len(sig), 1. /
fs)[:int(np.ceil(len(sig) / 2.))] # get freq axis
# Convert median filter length from Hz to samples
filt_len_samp = int(int(filt_len / (freqs[1] - freqs[0])) / 2 * 2 + 1)
spectrum = medfilt(np.abs(ft)**2. / (fs * len(sig)), filt_len_samp)
if f_range:
freqs, spectrum = trim_spectrum(freqs, spectrum, f_range)
return freqs, spectrum
def compute_spectrum_welch(sig,
fs,
avg_type='mean',
window='hann',
nperseg=None,
noverlap=None,
f_range=None,
outlier_percent=None):
"""Compute the power spectral density using Welch's method.
Parameters
-----------
sig : 1d or 2d array
Time series.
fs : float
Sampling rate, in Hz.
avg_type : {'mean', 'median'}, optional
Method to average across the windows:
* 'mean' is the same as Welch's method, taking the mean across FFT windows.
* 'median' uses median across FFT windows instead of the mean, to minimize outlier effect.
window : str or tuple or array_like, optional, default: 'hann'
Desired window to use. See scipy.signal.get_window for a list of available windows.
If array_like, the array will be used as the window and its length must be nperseg.
nperseg : int, optional
Length of each segment, in number of samples.
If None, and window is str or tuple, is set to 1 second of data.
If None, and window is array_like, is set to the length of the window.
noverlap : int, optional
Number of points to overlap between segments.
If None, noverlap = nperseg // 8.
f_range : list of [float, float] optional
Frequency range to sub-select from the power spectrum.
outlier_percent : float, optional
The percentage of outlier values to be removed. Must be between 0 and 100.
Returns
-------
freqs : 1d array
Frequencies at which the measure was calculated.
spectrum : 1d or 2d array
Power spectral density.
"""
# Calculate the short time fourier transform with signal.spectrogram
nperseg, noverlap = check_spg_settings(fs, window, nperseg, noverlap)
freqs, _, spg = spectrogram(sig, fs, window, nperseg, noverlap)
# Throw out outliers if indicated
if outlier_percent is not None:
spg = discard_outliers(spg, outlier_percent)
# Average across windows
spectrum = get_avg_func(avg_type)(spg, axis=-1)
# Trim spectrum, if requested
if f_range:
freqs, spectrum = trim_spectrum(freqs, spectrum, f_range)
return freqs, spectrum
def compute_spectrum_medfilt(sig, fs, filt_len=1., f_range=None):
"""Compute the power spectral density as a smoothed FFT.
Parameters
----------
sig : 1d or 2d array
Time series.
fs : float
Sampling rate, in Hz.
filt_len : float, optional, default: 1
Length of the median filter, in Hz.
f_range : list of [float, float], optional
Frequency range to sub-select from the power spectrum.
Returns
-------
freqs : 1d array
Frequencies at which the measure was calculated.
spectrum : 1d or 2d array
Power spectral density.
Examples
--------
Compute the power spectrum of a simulated time series as a smoothed FFT:
>>> from neurodsp.sim import sim_combined
>>> sig = sim_combined(n_seconds=10, fs=500,
... components={'sim_powerlaw': {}, 'sim_oscillation' : {'freq': 10}})
>>> freqs, spec = compute_spectrum_medfilt(sig, fs=500)
"""
# Take the positive half of the spectrum, since it's symmetrical
ft = np.fft.fft(sig)[:int(np.ceil(len(sig) / 2.))]
freqs = np.fft.fftfreq(len(sig), 1. / fs)[:int(np.ceil(len(sig) / 2.))]
# Convert median filter length from Hz to samples, and make sure it is odd
filt_len_samp = int(filt_len / (freqs[1] - freqs[0]))
if filt_len_samp % 2 == 0:
filt_len_samp += 1
spectrum = medfilt(np.abs(ft)**2. / (fs * len(sig)), filt_len_samp)
if f_range:
freqs, spectrum = trim_spectrum(freqs, spectrum, f_range)
return freqs, spectrum
def compute_spectrum_medfilt(sig, fs, filt_len=1., f_range=None):
"""Compute the power spectral density as a smoothed FFT.
Parameters
----------
sig : 1d or 2d array
Time series.
fs : float
Sampling rate, in Hz.
filt_len : float, optional, default: 1
Length of the median filter, in Hz.
f_range : list of [float, float], optional
Frequency range to sub-select from the power spectrum.
Returns
-------
freqs : 1d array
Frequencies at which the measure was calculated.
spectrum : 1d or 2d array
Power spectral density.
"""
# Take the positive half of the spectrum since it's symmetrical
ft = np.fft.fft(sig)[:int(np.ceil(len(sig) / 2.))]
freqs = np.fft.fftfreq(len(sig), 1. / fs)[:int(np.ceil(len(sig) / 2.))]
# Convert median filter length from Hz to samples, and make sure it is odd
filt_len_samp = int(int(filt_len / (freqs[1] - freqs[0])))
if filt_len_samp % 2 == 0:
filt_len_samp += 1
spectrum = medfilt(np.abs(ft)**2. / (fs * len(sig)), filt_len_samp)
if f_range:
freqs, spectrum = trim_spectrum(freqs, spectrum, f_range)
return freqs, spectrum
def compute_spectral_hist(sig,
fs,
window='hann',
nperseg=None,
noverlap=None,
nbins=50,
f_range=[0., 100.],
cut_pct=[0., 100.]):
"""Compute the distribution of log10 power at each frequency from the signal spectrogram.
Parameters
-----------
sig : 1d array
Time series of measurement values.
fs : float
Sampling rate, in Hz.
window : str or tuple or array_like, optional, default='hann'
Desired window to use. Defaults to a Hann window.
See scipy.signal.get_window for a list of windows and required parameters.
If array_like, the array will be used as the window and its length must be nperseg.
nperseg : int, optional
Length of each segment, in number of samples.
If None, and window is str or tuple, is set to 1 second of data.
If None, and window is array_like, is set to the length of the window.
noverlap : int, optional
Number of points to overlap between segments. If None, noverlap = nperseg // 2.
nbins : int, optional, default: 50
Number of histogram bins to use.
f_range : list of [float, float], optional, default: [0, 100]
Frequency range of the spectrogram to compute the histograms, as [start, end], in Hz.
cut_pct : list of [float, float], optional, default: [0, 100]
Power percentile at which to draw the lower and upper bin limits, as [low, high], in Hz.
Returns
-------
freqs : 1d array
Array of frequencies.
power_bins : 1d array
Histogram bins used to compute the distribution.
spectral_hist : 2d array
Power distribution at every frequency, nbins x fs 2D matrix.
Notes
-----
The histogram bins are the same for every frequency, thus evenly spacing the global min and max power.
"""
# Compute spectrogram of data
nperseg, noverlap = check_spg_settings(fs, window, nperseg, noverlap)
freqs, _, spg = spectrogram(sig,
fs,
window,
nperseg,
noverlap,
return_onesided=True)
# Get log10 power & limit to frequency range of interest before binning
ps = np.transpose(np.log10(spg))
freqs, ps = trim_spectrum(freqs, ps, f_range)
# Prepare bins for power - min and max of bins determined by power cutoff percentage
power_min, power_max = np.percentile(np.ndarray.flatten(ps), cut_pct)
power_bins = np.linspace(power_min, power_max, nbins + 1)
# Compute histogram of power for each frequency
spectral_hist = np.zeros((len(ps[0]), nbins))
for ind in range(len(ps[0])):
spectral_hist[ind], _ = np.histogram(ps[:, ind], power_bins)
spectral_hist[ind] = spectral_hist[ind] / sum(spectral_hist[ind])
# Flip output for more sensible plotting direction
spectral_hist = np.transpose(spectral_hist)
spectral_hist = np.flipud(spectral_hist)
return freqs, power_bins, spectral_hist
def compute_spectrum_welch(sig, fs, avg_type='mean', window='hann',
nperseg=None, noverlap=None,
f_range=None, outlier_percent=None):
"""Compute the power spectral density using Welch's method.
Parameters
----------
sig : 1d or 2d array
Time series.
fs : float
Sampling rate, in Hz.
avg_type : {'mean', 'median'}, optional
Method to average across the windows:
* 'mean' is the same as Welch's method, taking the mean across FFT windows.
* 'median' uses median across FFT windows instead of the mean, to minimize outlier effects.
window : str or tuple or array_like, optional, default: 'hann'
Desired window to use. See scipy.signal.get_window for a list of available windows.
If array_like, the array will be used as the window and its length must be nperseg.
nperseg : int, optional
Length of each segment, in number of samples.
If None, and window is str or tuple, is set to 1 second of data.
If None, and window is array_like, is set to the length of the window.
noverlap : int, optional
Number of points to overlap between segments.
If None, noverlap = nperseg // 8.
f_range : list of [float, float], optional
Frequency range to sub-select from the power spectrum.
outlier_percent : float, optional
The percentage of outlier values to be removed. Must be between 0 and 100.
Returns
-------
freqs : 1d array
Frequencies at which the measure was calculated.
spectrum : 1d or 2d array
Power spectral density.
Notes
-----
- Welch's method ([1]_) computes a power spectra by averaging over windowed FFTs.
References
----------
.. [1] Welch, P. (1967). The use of fast Fourier transform for the estimation of power
spectra: A method based on time averaging over short, modified periodograms.
IEEE Transactions on Audio and Electroacoustics, 15(2), 70–73.
DOI: https://doi.org/10.1109/TAU.1967.1161901
Examples
--------
Compute the power spectrum of a simulated time series using Welch's method:
>>> from neurodsp.sim import sim_combined
>>> sig = sim_combined(n_seconds=10, fs=500,
... components={'sim_powerlaw': {}, 'sim_oscillation': {'freq': 10}})
>>> freqs, spec = compute_spectrum_welch(sig, fs=500)
"""
# Calculate the short time Fourier transform with signal.spectrogram
nperseg, noverlap = check_spg_settings(fs, window, nperseg, noverlap)
freqs, _, spg = spectrogram(sig, fs, window, nperseg, noverlap)
# Throw out outliers if indicated
if outlier_percent is not None:
spg = discard_outliers(spg, outlier_percent)
# Average across windows
spectrum = get_avg_func(avg_type)(spg, axis=-1)
# Trim spectrum, if requested
if f_range:
freqs, spectrum = trim_spectrum(freqs, spectrum, f_range)
return freqs, spectrum
