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Is there any technology to help find out when an audio file is actually recorded?

Here is the problem:

Given an audio file, how can we find out when it is recorded? File creation time is useless because it can be altered.

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Only if there are clues in the recording, like a clock tower chiming in the background. You can identify where a recording took place by measuring the frequency of the power line hum that sneaks into every recording, but that only distinguishes 60 Hz countries from 50 Hz countries. en.wikipedia.org/wiki/Audio_forensics –  endolith Feb 27 '13 at 14:45
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2 Answers

up vote 3 down vote accepted

Baring information content that contains verifiable historical landmarks, you can't date data . Anything can be altered in a file, including the recorded content, so the data itself is no more reliable than a time stamp in a file header. The normal assumption about data files is that they can be faithfully reproduced over and over without degradation, so there is no time information in the data itself. You may be able to infer rough time estimates about the age of a recording based on certain qualities in the recording (assuming that the data has been unaltered). For example a digital reproduction of an analog recoding that was originally mastered on a particular media has qualities that may be discernible upon analysis. If you can identify qualities that indicate the type of equipment used to capture the audio and type of media the audio was captured on, you may be able to infer that the recording is from a certain time period.

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If there is some background hum due to AC mains interferences, you can match that with historical records of the fluctuation patterns in mains frequency within the electricity grid. Reference here.

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Color me skeptical on this one. –  Jim Clay Feb 27 '13 at 17:14
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Apparently already used for a case in court: bbc.co.uk/news/science-environment-20629671 –  pichenettes Feb 27 '13 at 20:59
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A lot of people have been convicted on fingerprint proof that was crap. Based on what I know of correlations I think it is highly likely that they will make false positives. That doesn't mean that they won't be able to sell it to a jury though. –  Jim Clay Feb 27 '13 at 22:27
    
It sounds impressive, all that technology and what not, but actually finding a true match, that is the stuff of spy novels. –  user2718 Feb 28 '13 at 4:59
    
+1 for creativity –  nibot Mar 3 '13 at 9:36
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