Feature Extraction Method for Hidden Information in Audio Streams Based on HM-EMD

Figure 2

IMF waveforms with significant hidden components in different environments of the audio stream. (a) Airport luggage roller: IMF16, low freq. (b) Metro rail joint collision: IMF14, low freq. (c) Chirm: IMF1, high freq. (d) Steps: IMF10, medium freq. (e) Vehicles from far to near: IMF1, high freq. (f) Tram acceleration: IMF4, medium and high freq.

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