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Table 3 Cough sound signal extracted features.

From: Classification of voluntary cough sound and airflow patterns for detecting abnormal pulmonary function

  Time Series
1 Cough Length: length from the start of the cough until 99.4% of the cough energy is achieved (s)
2 L-ratio: Cough flow length/cough sound length
3 Skewness: where μ, and σ are the mean, and the standard deviation of the cough sound signal respectively.
4 Kurtosis: where μ, and σ are the mean, and the standard deviation of the cough sound signal respectively.
5 Crest Factor: maximum sound pressure wave/Root Mean Square "RMS" sound
  Frequency Series
6 Dominant Frequency: the frequency with the most power present in the cough sound pressure wave (Hz)
7 Total energy
8-24 Octave Analysis (1-17)**
25 Total Power: total power in the cough sound signal (W)
26 Peak Power: maximum power level (W)
27 Average Power: Average power over all frequency ranges (W)
28 Sound beta: the inverse power law 1/fβ of the power spectrum [22].
29 Sound Wavelet: a wavelet parameter based on the variability in the wavelet detail coefficients found in the wavelet decomposition of the cough sound
30 Ratio: mean spectrogram intensity/max spectrogram intensity
31 Peaks: this counts the number of peaks in the spectrogram that meet a given threshold
32-51 Spec1 - Spec20: The spectrogram is broken into 20 evenly spaced time intervals. For each interval, the maximum energy is found, and the corresponding frequency is saved.
52-81 Spec21 - Spec50: The spectrogram is broken into 30 evenly space time intervals. For each interval, the average frequency is calculated and saved.
82-111 Spec51 - Spec80: The spectrogram is broken into 30 evenly spaced frequency intervals. For each frequency interval the time at which half of the energy is attained is saved.
  1. **Octave analysis: the power of cough sound pressure wave is broken into octaves (frequency bands) and the power found in each octave is calculated in each band. Analysis was stopped at 18,102 Hz, because only 2% of the energy remains above Oct17.