Tampering Detection Scheme for Speech Signals using Formant Enhancement Based Watermarking

Unauthorized tampering in speech signals has brought serious problems when verifying their originality and integrity. Digital watermarking can effectively check if the original speech signals have been tampered by embedding digital data into them. To be effective, watermarking method should be implemented according to four requirements of (1) inaudibility to human auditory system, (2) blindness to extract watermarks without referring to the host signal, (3) robustness against speech processing, and (4) fragility against tampering. This paper proposes a tampering detection scheme for speech signals based on formant enhancement-based watermarking. Watermarks are embedded as slight enhancement of formant by symmetrically controlling a pair of linear spectral frequencies (LSFs) of corresponding formant. Such embedding concept not only enables the proposed scheme to be inaudible but also provides the possibilities of robustness against speech processing and fragility against tampering. The proposed scheme was evaluated with respect to inaudibility, robustness, and fragility compared with other two typical methods. The evaluation results showed that the proposed scheme could provide satisfactory performance for all the requirements, and had the ability to detect tampering in speech signals.