Study on Inaudible Speech Watermarking Method Based on Spread-Spectrum Using Linear Prediction Residue

A reliable speech watermarking technique must balance satisfying four requirements: inaudibility, robustness, blind detectability, and confidentiality. A previous study proposed a speech watermarking technique based on direct spread spectrum (DSS) using a linear prediction (LP) scheme, i.e., LP-DSS, that could simultaneously satisfy these four requirements. However, an inaudibility issue was found due to the incorporation of a blind detection scheme with frame synchronization. In this paper, we investigate the feasibility of utilizing a psychoacoustical model, which simulates auditory masking, to control the suitable embedding level of the watermark signal to resolve the inaudibility issue in the LP-DSS scheme. Evaluation results confirmed that controlling the embedding level with the psychoacoustical model, with a constant scaling factor setting, could balance the trade-off between inaudibility and detection ability with a payload up to 64 bps.