Predicting gastrointestinal bleeding and audio biomarkers based on machine learning analysis of bowel sounds

Table 3 Reference for the characteristics of bowel sounds

Feature type	Feature	Physical meaning
Time domain	Max, Min, Mean, Peak_to_Peak	Amplitude peak, minimum, arithmetic mean value, difference between maximum and minimum
	Abs_Mean, Variance, Std_Dev, RMS	Amplitude absolute value average, variance, standard, root mean square
	Waveform_Length, Skewness	Cumulative change magnitude, signal distribution asymmetry
	Kurtosis, Crest_Factor	Signal peakiness, normalized fourth moment
	Zero_Crossing_Rate_Mean, Varian, Skewne	Signal oscillation frequency, oscillation degree, oscillation skewness characteristic
	Q1, Q3, interquartile range	Amplitude 25th, 75th percentile value, range between 25th and 75th
	Shape_Factor, Impluse_Factor	Regularity, peak component intensity of signals
	Margin_Factor, Hjorth_Activity, Hjorth Mobility	Signal large amplitude change index, the total power of the signal, contraction frequency fluctuation
	Autocoor_Peak, Fractal_Dimension, Energy, Avg_energy	Maximum signal self-similarity, signal complexity/irregularity, total squared amplitude, energy per sample
Frequency domain	Spectral_Centroid, Slope, Bandwidth, Flatness	Signal frequency, variance around of centroid, tonal vs noise-like character
	Spectral_Rolloff85, Rolloff95, Steepness	Frequency point with 85%, 95% total energy, the average energy ratio of high frequency to low frequency
	Band_Energy_[1-5]	50-100 Hz, 100-500 Hz, 500-1000 Hz, 1000-2000 Hz, 2000-4000 Hz
	MFCC_Mean_[1-13]	Spectral envelope characteristics
	MFCC_Var_[1-13]	Spread of spectral envelope
	Spectral Steepness, PSD_Peak, Harmonic_Ratio	Average spectral slope, maximum power spectral density, harmonic content proportion
Time-frequency domain	Wavelet_Energy_[0-2]	Wavelet coefficient energy
	Wavelet_Kurtosis_[0-2]	Peakiness in wavelet coefficients
	STFT_Energy_Kurtosis	Peak concentration of short-time Fourier transform energy
Nonlinear characteristics	Hjorth_Complexity	The complexity of signal changes
	Wavelet_Entropy_[0-2], STFT_Energy_Entropy	Signal complexity in wavelet domain, uncertainty in time-frequency energy distribution