The efficient wavelet masking is a scheme of speech-in-speech hiding based on the ability of adaptation of speech signals under the hypothesis “any (speech) secret signal may seem similar to a (speech) host signal if its wavelet coefficients are sorted” (Ballesteros L & Moreno A, 2012). In this paper, we delimitate the conditions under which the above hypothesis is true, as follows: (i) the secret and host signals must belong to legible voice signals, (ii) both signals must have the same sampling frequency, (iii) both signals must have the same time-frame, and finally (iv) the ratio between the non-zero coefficients of them should be in the interval [0.8 1.2]. Experimental tests were conducted to demonstrate the hypothesis on different cases: vowel to vowel, message to message and vowel & message, in three languages: English, French, and German. The parameter used to measure the similarity between the adapted secret message and the host signal is the squared Pearson correlation coefficient, r2. The results demonstrate that the hypothesis is true under the theoretical conditions because in all the test cases r2 was closed to 1 and the p-value was lower than 0.05.

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