Update to new smoothing algorithm. Should be made faster.
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@ -1,7 +1,7 @@
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#!/usr/bin/env python3
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# -*- coding: utf-8 -*-
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"""
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Author: C. Jansen, J.A. de Jong - ASCEE V.O.F.
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Author: T. Hekman, C. Jansen, J.A. de Jong - ASCEE V.O.F.
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Smooth data in the frequency domain.
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@ -9,30 +9,17 @@ TODO: This function is rather slow as it uses [for loops] in Python. Speed up.
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NOTE: function requires lin frequency spaced input data
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TODO: accept input data that is not lin spaced in frequency
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TODO: it makes more sense to output data that is log spaced in frequency
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Cutoff frequencies of window taken from
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http://www.huennebeck-online.de/software/download/src/index.html 15-10-2021
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math --> ReduceSpectrum.c --> ReduceSpectrum::smoothLogXScale()
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fl = fcenter / sqrt(2^(1/Noct)) # lower cutoff
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fu = fcenter * sqrt(2^(1/Noct)) # upper cutoff
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such that:
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sqrt(fl * fu) = fcenter
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fu = 2^(1/Noct) * fl
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Smoothing window taken from
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https://www.ap.com/technical-library/deriving-fractional-octave-spectra-from-
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the-fft-with-apx/ 15-10-2021
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g = sqrt( 1/ ([1+[(f/fm - fm/f)*(1.507*b)]^6]) )
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where b = 3 for 1/3rd octave, f = frequency, fm = mid-band frequency, g = gain.
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Gain is related to magnitude; power is related to gain^2
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TODO: Make SmoothSpectralData() multi-dimensional array aware.
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TODO: Smoothing does not work due to complex numbers. Is it reasonable to
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smooth complex data? If so, the data could be split in magnitude and phase.
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"""
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__all__ = ['SmoothingType', 'smoothSpectralData', 'SmoothingWidth']
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from enum import Enum, unique
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import bisect
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import copy
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import numpy as np
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from numpy import log2, pi, sin
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@unique
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@ -73,6 +60,22 @@ class SmoothingType:
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# TO DO: check if everything is correct
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# TO DO: add possibility to insert data that is not lin spaced in frequency
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# Integrated Hann window
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def intHann(x1, x2):
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"""
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Calculate integral of (part of) Hann window.
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If the args are vectors, the return value will match those.
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Args:
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x1: lower bound [-0.5, 0.5]
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x2: upper bound [-0.5, 0.5]
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Return:
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Integral of Hann window between x1 and x2
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"""
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x1 = np.clip(x1, -0.5, 0.5)
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x2 = np.clip(x2, -0.5, 0.5)
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return (sin(2*pi*x2) - sin(2*pi*x1))/(2*pi) + (x2-x1)
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def smoothCalcMatrix(freq, sw: SmoothingWidth):
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@ -83,12 +86,18 @@ def smoothCalcMatrix(freq, sw: SmoothingWidth):
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Returns:
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freq: array frequencies of data points [Hz]
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Q: matrix to smooth power: {fsm} = [Q] * {fraw}
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Q: matrix to smooth, power: {fsm} = [Q] * {fraw}
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Warning: this method does not work on levels (dB)
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According to Tylka_JAES_SmoothingWeights.pdf
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"A Generalized Method for Fractional-Octave Smoothing of Transfer Functions
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that Preserves Log-Frequency Symmetry"
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https://doi.org/10.17743/jaes.2016.0053
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par 1.3
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eq. 16
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"""
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# Settings
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tr = 3 # truncate window after 2x std; shorter is faster and less accurate
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Noct = sw.value[0]
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assert Noct > 0, "'Noct' must be absolute positive"
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assert np.isclose(freq[-1]-freq[-2], freq[1]-freq[0]), "Input data must "\
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@ -100,44 +109,41 @@ def smoothCalcMatrix(freq, sw: SmoothingWidth):
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L = len(freq)
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Q = np.zeros(shape=(L, L), dtype=np.float16) # float16: keep size small
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Q[0, 0] = 1 # in case first point is skipped
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x0 = 1 if freq[0] == 0 else 0 # Skip first data point if zero frequency
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x0 = 1 if freq[0] == 0 else 0 # skip first data point if zero frequency
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# Loop over indices of raw frequency vector
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for x in range(x0, L):
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# Find indices of data points to calculate current (smoothed) magnitude
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#
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# Indices beyond [0, L] point to non-existing data. Beyond 0 does not
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# occur in this implementation. Beyond L occurs when the smoothing
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# window nears the end of the series.
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# If one end of the window is truncated, the other end
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# could be truncated as well, to prevent an error on magnitude data
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# with a slope. It however results in unsmoothed looking data at the
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# end.
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fc = freq[x] # center freq. of smoothing window
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fl = fc / np.sqrt(2**(tr/Noct)) # lower cutoff
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fu = fc * np.sqrt(2**(tr/Noct)) # upper cutoff
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Noct /= 2 # corr. factor: window @ -3dB at Noct bounds (Noct/1.5 for -6dB)
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ifreq = freq/(freq[1]-freq[0]) # frequency, normalized to step=1
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ifreq = np.array(ifreq.astype(int))
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ifreqMin = ifreq[x0] # min. freq, normalized to step=1
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ifreqMax = ifreq[L-1] # max. freq, normalized to step=1
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sfact = 2**((1/Noct)/2) # bounds are this factor from the center freq
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# If the upper (frequency) side of the window is truncated because
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# there is no data beyond the Nyquist frequency, also truncate the
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# other side to keep it symmetric in a log(frequency) scale.
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# So: fu / fc = fc / fl
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fNq = freq[-1]
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if fu > fNq:
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fu = fNq # no data beyond fNq
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fl = fc**2 / fu # keep window symmetric
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kpmin = np.floor(ifreq/sfact).astype(int) # min freq of window
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kpmax = np.ceil(ifreq*sfact).astype(int) # max freq of window
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# Find indices corresponding to frequencies
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xl = bisect.bisect_left(freq, fl) # index corresponding to fl
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xu = bisect.bisect_right(freq, fu)
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for ff in range(x0, L): # loop over input freq
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# Find window bounds and actual smoothing width
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# Keep window symmetrical if one side is truncated
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if kpmin[ff] < ifreqMin:
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kpmin[ff] = ifreqMin
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kpmax[ff] = np.ceil(ifreq[ff]**2/ifreqMin) # decrease smooth width
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if np.isclose(kpmin[ff], kpmax[ff]):
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kpmax[ff] += 1
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NoctAct = 1/log2(kpmax[ff]/kpmin[ff])
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elif kpmax[ff] > ifreqMax:
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kpmin[ff] = np.floor(ifreq[ff]**2/ifreqMax) # decrease smoothwidth
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kpmax[ff] = ifreqMax
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if np.isclose(kpmin[ff], kpmax[ff]):
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kpmin[ff] -= 1
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NoctAct = 1/log2(kpmax[ff]/kpmin[ff])
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else:
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NoctAct = Noct
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xl = xu-1 if xu-xl <= 0 else xl # Guarantee window length >= 1
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# Calculate window
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xg = np.arange(xl, xu) # indices
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fg = freq[xg] # [Hz] corresponding freq
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gs = np.sqrt( 1/ ((1+((fg/fc - fc/fg)*(1.507*Noct))**6)) ) # raw windw
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gs /= np.sum(gs) # normalize: integral=1
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Q[x, xl:xu] = gs # add to matrix
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kp = np.arange(kpmin[ff], kpmax[ff]+1) # freqs of window
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Phi1 = log2((kp - 0.5)/ifreq[ff]) * NoctAct # integr. bounds Hann wind
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Phi2 = log2((kp + 0.5)/ifreq[ff]) * NoctAct
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W = intHann(Phi1, Phi2) # smoothing window
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Q[ff, kpmin[ff]-ifreq[0]:kpmax[ff]-ifreq[0]+1] = W
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# Normalize to conserve input power
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Qpower = np.sum(Q, axis=0)
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@ -149,57 +155,40 @@ def smoothCalcMatrix(freq, sw: SmoothingWidth):
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def smoothSpectralData(freq, M, sw: SmoothingWidth,
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st: SmoothingType = SmoothingType.levels):
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"""
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Apply fractional octave smoothing to magnitude data in frequency domain.
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Smoothing is performed to power, using a sliding Gaussian window with
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variable length. The window is truncated after 3x std at either side.
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The implementation is not exact, because f is linearly spaced and
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fractional octave smoothing is related to log spaced data. In this
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implementation, the window extends with a fixed frequency step to either
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side. The deviation is largest when Noct is small (e.g. coarse smoothing).
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07-05-2021
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Update 16-01-2023: speed up algorithm
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- Smoothing is performed using matrix multiplication
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- The smoothing matrix is not calculated if it already exists
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Apply fractional octave smoothing to data in the frequency domain.
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Args:
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freq: array of frequencies of data points [Hz] - equally spaced
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M: array of either power, transfer functin or dB points. Depending on
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M: array of data, either power or dB
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the smoothing type `st`, the smoothing is applied.
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sw: smoothing width
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st: smoothing type = data type of input data
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Returns:
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freq : array frequencies of data points [Hz]
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Msm : float smoothed magnitude of data points
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"""
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# TODO: Make this function multi-dimensional array aware.
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# Safety
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MM = copy.deepcopy(M)
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Noct = sw.value[0]
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assert len(M) > 0, "Smoothing function: input array is empty" # not sure if this works
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assert len(MM) > 0, "Smoothing function: input array is empty" # not sure if this works
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assert Noct > 0, "'Noct' must be absolute positive"
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if Noct < 1:
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raise Warning('Check if \'Noct\' is entered correctly')
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assert len(freq) == len(M), 'f and M should have equal length'
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assert len(freq) == len(MM), "f and M should have equal length"
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# if st == SmoothingType.ps:
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# assert np.min(M) >= 0, 'absolute magnitude M cannot be negative'
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if st == SmoothingType.levels and isinstance(M.dtype, complex):
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if st == SmoothingType.ps:
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assert np.min(MM) >= 0, 'Power spectrum values cannot be negative'
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if st == SmoothingType.levels and isinstance(MM.dtype, complex):
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raise RuntimeError('Decibel input should be real-valued')
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# Initialize
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L = M.shape[0] # number of data points
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# Convert to power
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if st == SmoothingType.levels:
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P = 10**(MM/10) # magnitude [dB] --> power
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P = 10**(MM/10)
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elif st == SmoothingType.ps:
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P = MM
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else:
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P = MM # data already given as power
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# TODO: This does not work due to complex numbers. Should be split up in
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# magnitude and phase.
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# elif st == SmoothingType.tf:
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# P = P**2
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raise RuntimeError(f"Incorrect SmoothingType: {st}")
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# P is power while smoothing. x are indices of P.
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Psm = np.zeros_like(P) # Smoothed power - to be calculated
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@ -225,6 +214,7 @@ def smoothSpectralData(freq, M, sw: SmoothingWidth,
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# Apply smoothing
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Psm = np.matmul(Q, P)
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# Convert to original format
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if st == SmoothingType.levels:
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Psm = 10*np.log10(Psm)
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