Audio forensics
Audio forensics is the field of forensic science relating to the acquisition, analysis, and evaluation of sound recordings that may ultimately be presented as admissible evidence in a court of law or some other official venue. Audio forensic evidence may come from a criminal investigation by law enforcement or as part of an official inquiry into an accident, fraud, accusation of slander, or some other civil incident. The primary aspects of audio forensics are establishing the "authenticity" of audio evidence, performing "enhancement" of audio recordings to improve speech intelligibility and the audibility of low-level sounds, and "interpreting  and documenting" sonic evidence, such as identifying talkers, transcribing dialog, and reconstructing crime or accident scenes and timelines. Modern audio forensics makes extensive use of digital signal processing, with the former use of analog filters now being obsolete. Techniques such as adaptive filtering and discrete Fourier transforms are used extensively. The field of audio forensics was largely established in 1973 during the Watergate scandal. A federal court commissioned a panel of audio engineers to investigate the gaps in President Nixon's Watergate Tapes, which were secret recordings U.S. President Richard Nixon made while in office. The probe found nine separate  sections of a vital tape had been erased. The report gave rise to new techniques to analyze magnetic tape. Recent advances in audio forensics techniques include voice biometrics and electrical network frequency analysis.