I wasn’t originally going to post about this, since the story was linked from Slashdot and other places. However, it came up at dinner last night; Andrew was asking me about it this afternoon, and I promised him a link.
So: here’s a link to The Register‘s article on authenticating recordings using AC power line frequency fluctuations.
At the Metropolitan Police’s digital forensics lab in Penge, south London, scientists have created a database that has recorded these deviations once every one and a half seconds for the last five years. Over a short period they form a unique signature of the electrical frequency at that time, which research has shown is the same in London as it is in Glasgow.
On receipt of recordings made by the police or public, the scientists are able to detect the variations in mains electricity occuring at the time the recording was made. This signature is extracted and automatically matched against their ENF database, which indicates when it was made.
I’d want to see a lot more scientific validation of this before I’d consider it acceptable as evidence. One of the points I made during the dinner discussion is that much of modern forensics is based on sloppy or incomplete science. For example:
- the FBI’s use of bullet composition analysis, now discredited. (60 Minutes/WP story. FBI press release.)
- Serial killer profiling. (Malcom Gladwell’s article.)
- At the very least, there seem to be open questions about fingerprint evidence. (Michael Specter in the New Yorker.)
Balko is all over this, too; you should be reading him regularly if you care about this stuff.