Imperceptible data hiding in the encoded bits of ACELP codebook

This paper describes an invisible data hiding method for embedding data in encoded bits of the ACELP parameters for the G.723.1 speech coder, which is already being applied widely in Voice-over-Internet Protocol. We show that the encoded bits of the ACELP codebook excitation pulse positions are more appropriate for message hiding than the encoded bits of other speech parameters. The score of an imperceptibility assessment shows that the perceptual evaluation of speech quality (PESQ) value is reduced slightly, by 0.112, compared to that of a carrier voice that is not inserted information. Evaluation reports present that our proposed scheme can attain complete invisibility and obtains a message-hiding volume of on average 400 bps for a 5.3 kbit/s coding rate. Objective quality measurements verify that our proposed hiding scheme can achieve an inaudible distortion in the occult-speech quality.