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

Algorithm 2

Heuristic empirical mode decomposition with a masking signal.

	Input: signal x (t), supposed IMF number i
	Output: intrinsic mode function, IMF
(1)	= x (t), i = 1.
(2)	Get the first IMF of the signal residual , calculate the mean and variance of , and use formula (8) to determine whether there is a hiding jump point. Variable analysis window is constructed according to the hiding jump point and is segmented.
(3)	Construct mask signal for each : .
(4)	Do EMD on and ; get the first IMF and .
(5)	Let  = ( + )/2, and splice all the divided pieces.
(6)	i = i + 1,  =  – , return to step 2, until , or no new IMF is required.