An Automatic Watermarking in CELP Speech Codec Based on Formant Tuning

This paper proposes the unification of the codeexcited linear prediction (CELP) codec process with watermarking based on formant tuning. The serial problem in atermarking and then encoding with the CELP codec was thereby reduced by using the proposed method which also ncreased the bit detection rate. We took advantage of two key properties: I) humans do not perceive alterations applied to formants and II) CELP and watermarking based on formant tuning methods utilize lineal prediction coefficients. We investigated the inaudibility and robustness of the proposed method by carrying out three different experiments using log-spectrum distance (LSD), the perceptual evaluation of speech quality (PESQ) and the bit detection rate (BDR). The results indicated that the proposed method satisfied the inaudibility requirement when watermarking was applied to the CELP codec, which increased the watermarking detection rate.