Watermarking Method for Speech Signals based on Modifications to LSFs

We propose a method of speech watermarking based on modifications to line spectral frequencies (LSFs) of original speech. LSFs were derived from each frame with linear prediction (LP) analysis and watermarks were embedded into them by using the quantization index modulation (QIM) of different quantization steps. We took into consideration inaudibility and robustness that were influenced by minor modifications to LSFs. The proposed approach was evaluated with two kinds of experiments with respect to inaudibility and robustness against different speech codecs and general processing. The results from the evaluations revealed that the proposed approach not only had high rate of bit detection while keeping the original sound quality undistorted but also good robustness against general speech processing.