WIRED has a piece on
the state of audio forensics today, or how much information can be extracted from an audio recording:
None of the sharp-eared audio professionals at the Javits Convention Center caught another edit on Allen's criminal-investigation tape. Allen digitally hid that edit behind a speaker's cough, and it was only revealed with the help of some sophisticated forensic software.
Catalin Grigoras, a forensic examiner from Bucharest, told the workshop how he uses the frequency signatures of local electrical power sources to pinpoint when and where recordings were made. According to Grigoras, digital recorders that are plugged into electrical sockets capture the frequency signature of the local power supply -- a signature that varies over time.
In one case, Grigoras claims to have identified the date of a recording broadcast in Europe, but made in the Middle East, "probably in the mountains, or in a cave," he says. He didn't mention any names, but it was hard not to think of Al Qaeda.