Audio and Document Steganography

WAV audio files store uncompressed 16-bit or 24-bit PCM audio samples. Like image LSB steganography, we can replace the least significant bit of each audio sample with a hidden bit. The modification changes each sample by at most 1 amplitude unit out of 32768, which is 0.003 percent of the full scale and completely inaudible to human listeners under normal conditions.

Phase coding divides an audio signal into short segments and encodes hidden bits by shifting the phase of each segment. Phase differences between adjacent segments are preserved to avoid audible artefacts. Because the human ear is relatively insensitive to absolute phase values, small phase modifications carry hidden data without detectably changing the sound. Phase coding achieves better imperceptibility than LSB at the same payload rate.