  In this article, the authors discuss the problem of forensic authentication
of digital audio recordings. Although forensic audio has been addressed in
several articles, the existing approaches are focused on analog magnetic
recordings, which are less prevalent because of the large amount of digital
recorders available on the market (optical, solid state, hard disks, etc.). An
approach based on digital signal processing that consists of spread spectrum
techniques for speech watermarking is presented. This approach presents the
advantage that the authentication is based on the signal itself rather than the
recording format. Thus, it is valid for usual recording devices in
police-controlled telephone intercepts. In addition, our proposal allows for
the introduction of relevant information such as the recording date and time
and all the relevant data (this is not always possible with classical systems).
Our experimental results reveal that the speech watermarking procedure does not
interfere in a significant way with the posterior forensic speaker
identification.
