In forensic audio examination, standard listening and visual sound spectrogram analysis methods often lead to incorrect conclusions due to the losses in data when the tape is copied. Furthermore, conducting the standard examinations on audio files which are digitally edited and re-recorded on the tapes, leaving very little trace behind, also result in incorrect decisions made by forensic experts. In this study, a novel and a very simple technique was developed, where the electronic edit traces on an electronically edited tape become easily detectable on copy generation tapes. Thus, regardless of the duplication speed, copied tapes can be analyzed for their originality and integrity with this technique and digital changes on them can be determined. The technique is based on increasing the tape playback speed by modifying the playback system of a player device. This essentially alters the time base of the signal and expands the low frequency scale of the recording in the frequency domain, and makes manipulation marks easily observable. It can be applied to most analog magnetic tape recorder devices. Edit marks can be precisely detected with minimal loss of time by using specially modified nonstandard devices rather than available conventional standard devices.
Key words: Forensic audio, copy generation tapes, analogue audio tape editing, authentication, tampering
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