Speech Information Hiding by Modification of LSF Quantization Index in CELP Codec

A prospective method for securing digital speech communication is by hiding the information within the speech. Most of the speech information hiding methods proposed in prior research are lacking in robustness when dealing with the encoding process (e.g. the code-excited linear prediction (CELP) codec). The CELP codecs provide a codebook that represents the encoded signal at a lower bit rate. As essential features in speech coding, line spectral frequencies (LSFs) are generally included in the codebook. Consequently, LSFs are considered as a prospective medium for information hiding that is robust against CELP codecs. In this paper, we propose a speech information hiding method that modifies the least significant bit of the LSF quantization obtained by a CELP codec. We investigated the feasibility of our proposed method by objective evaluation in terms of detection accuracy and inaudibility. The evaluation results confirmed the reliability of our proposed method with some further potential improvement (multiple embedding and varying segmentation lengths). The results also showed that our proposed method is robust against several signal processing operations, such as resampling, adding Gaussian noise, and several CELP codecs (i.e., the Federation Standard-1016 CELP, G.711, and G.726).