US Patent 7555432 Audio steganography method and apparatus using cepstrum modification

Audio steganography methods and apparatus using cepstral domain techniques to make embedded data in audio signals less perceivable. One approach defines a set of frames for a host audio signal, and, for each frame, determines a plurality of masked frequencies as spectral points with power level below a masking threshold for the frame. The two most commonly occurring masked frequencies f1 and f2 in the set of frames are selected, and a cepstrum of each frame is modified to produce complementary changes of the spectrum at f1 and f2 to correspond to a desired bit value. Another aspect of the invention involves determining a masking threshold for a frame, determining masked frequencies within the frame having a power level below threshold, obtaining a cepstrum of a sinusoid at a selected masked frequency, and modifying the frame by an offset to correspond to an embedded data value, the offset derived from the cepstrum.