Micah Loewinger: This is On the Media, I’m Micah Loewinger, filling in for Brooke Gladstone. Okay, so this next mystery is a little different. It has to do with an obscure form of audio forensics –– a technology called electrical network frequency analysis or ENF.
Jen Munson: Hi!
Micah Loewinger: That’s Jen Munson, she’s On the Media’s technical director. Her job is to make the hosts, producers, reporters, and the people we speak to sound as clean and clear as possible.
Jen Munson: my approach is mostly to find the thing that I like in someone's voice and bring that out.
Micah Loewinger: I called her up to tell her about ENF analysis, though she didn’t know that. I just said I was working on an episode about audio mysteries.
Jen Munson: Audio mysteries!
Micah Loewinger: (laughs)
Micah Loewinger: I told her that I had sent a scientist some recordings of me interviewing people on our show –– just my side of the conversation, my voice –– and using ENF analysis, this researcher was able to tell me the day and time, almost to the exact second, that I recorded each interview.
Jen Munson: Really?
Micah Loewinger: Yeah.
Jen Munson: Forensic audio is really fascinating to me. I would think there would be a way to compare it to known other recordings, you know, traffic sounds… like environmental sounds around you.
Micah Loewinger: Okay. That's a great guess, but that's not right.
Jen Munson: That’s not right!? Tell me now I want to know.
Nasir Memon: hi, I'm Nasir Memon. I'm a professor here at NYU Tandon School of Engineering in the Computer Science and Engineering department.
Micah Loewinger: Nasir oversees the group at New York University that published papers on ENF analysis as recently as this year. They get funding from The Defense Advanced Research Projects Agency, aka DARPA, the research arm of the Department of Defense. This type of audio forensics has been studied in academia for a couple decades but its use by law enforcement is what caught his eye.
Nasir Memon: To my understanding the first folks that had done it was the London Metropolitan Police.
Micah Loewinger: In 2010 a specialist at the Metropolitan Police department described ENF as the “most significant development in the field since techniques were developed to analyze the Watergate Tapes.” Referring to the early 70s, when a team of nascent audio forensics engineers spent months and months trying to recover the missing 18 minutes in Richard Nixon’s White House recordings.
Micah Loewinger: Nasir explained to me that for ENF analysis to work, he needs to find something very specific in the recordings I sent him, a bit of interference that Jen Munson is very familiar with...
Jen Munson: You'll see on the graph, you’re getting… the low rumble.
Micah Loewinger: I had Jen Munson use a fancy audio equalizer tool to look at the different frequencies in a recording I sent to Nasir’s team.
Jen Munson: There's a little bit of this like hum, 60 hertz. [00:26:10] Can you hear that?
Micah Loewinger: I think it's kind of imperceptible in this recording.
Jen Munson: But my ears are tuned to hear it.
Micah Loewinger: Audio engineers will tell you that this 60 hertz hum contaminates all kinds of recordings.
Jen Munson: That’s the first thing I’m approaching is getting rid of that sound… you hear it a lot on guitar amps. You hear it with…
Nasir Memom: My refrigerator, a TV…
Jen Munson: Elevators in buildings...
Nasir Memom: A refrigerator…
Jen Munson: It’s very common!
Micah Loewinger: Many of our electrical things, all around us, are constantly buzzing at 60 hertz, or a harmonic like 120 hertz. And what we’re hearing, or not hearing, is the electrical grid. The companies that manage our power, in my case, Con Edison in New York, are required by law to maintain that 60 hertz output.
Nasir Memon: But it’s unable to keep it exactly at 60… lights turn on and off, and people turn on devices. And so it’s trying to cater to the load. It doesn't want to produce too much electricity.
Micah Loewinger:: The demand for electricity is constantly changing based on what's plugged in.
Nasir Memon And the production mechanism is trying to keep pace with it and it doesn’t succeed… in maintaining it to exactly 60. So it becomes 59.8. 60.1.
Micah Loewinger: if you were to map the frequency over time, it would not be the straight 60 hertz. It would be this ever so slightly wiggle.
Nasir: Yes, ever so slightly wiggle… the utility companies, they have to measure this and report it to the government… but we can measure it too.
Nasir’s former grad student Saffet Vatansever built a very simple computer that records the wiggle from the grid every second or so. And when I sent Saffet my recordings, he isolated the 60-ish hertz hum, which might have come from my laptop charger plugged in a few feet from my microphone.
Nasir Memon: So he would pull out the data for the last three months that we've been capturing.
Micah Loewinger: I told Saffet that I often recorded my interviews a couple weeks before they’re aired, which a forensic specialist would quickly figure out anyway. But mostly so he wouldn’t have to spend unnecessary time cycling through years worth of data.
Nasir Memon: and then he would run an algorithm on the sound… using a sliding window. … every 20 seconds he sort of slides it over, And at some point where it was the right time, … matches, matches, matches
Micah Loewinger: Which is how he guessed the time of three of my recordings within 10 seconds.
Jen Munson: WOW!
Micah Loewinger: I just love the fact that it's such “a one man's trash is another man's treasure” thing. For you and audio engineers, you would get rid of it. The thing that makes your job slightly harder is actually like this forensic fossil that can be dug up to glean information about when something happened, when the recording was made.
Jen Munson: I’m blown away.
Micah Loewinger: Even though ENF has been around for nearly 2 decades, it doesn’t seem to have caught on in any significant way in the US. I reached out to an editor at Bellingcat, the cutting-edge investigative outlet known for its use of data and tech - they knew about ENF analysis but weren't familiar with journalists using it. I couldn’t find any court records mentioning its use by American law enforcement.
Micah Loewinger: Catalin Grigoras, one of the early developers of ENF, told me it's often used for checking to see if media has been edited or tampered with –– you can compare the hum in a piece of media to the data from the grid to see if it’s been spliced or re-arranged. Other scholars have referenced the Osama Bin Laden cave videos as a hypothetical application –– investigations in which the ability to learn which electrical grid a person is near might offer up new leads. But the issue here is that the technology only works if A, the hum, is captured in the recording, which is a bit of a crapshoot, and B, you have access to the right grid data. Nasir Menon.
Nasir Memon: If I was running an intelligence agency, I would make sure I'm capturing everywhere in the world.
Micah Loewinger: Do you think… American intelligence agencies are interested in ENF?
Nasir Memon: Intelligence won't tell me. Right. And if I knew, I may not be able to tell you as well, which I don't.
Micah Loewinger: Do I believe you?
Nasir Memon I don't have any secret clearance.
Micah Loewinger: You mentioned that the study was funded by DARPA. … It does seem like you are helping develop a technology that could be used for surveillance.
Nasir Memon: We are scientists. We like to further science. And science can be used for good and bad. So we just leave that question aside quite often. It just gets very, very, very complicated.
Micah Loewinger: He told me at one point in his team’s research, he had considered collecting way more data…
Nasir Memon: Even different countries. Make it public. Put a tool whereby you submit a video and then I'll tell you what time it was taken. And then I thought, that's going too far. That's going too far because. The ethical issue started coming up to me.
Micah Loewinger: What if a stalker wants to track somebody down using videos you posted on Instagram.
Nasir Memon: Yeah, that's why I didn't do it. The other reason… I don't think there was enough money in it. I'm not trying to say I'm a very ethical person. If there was money maybe I would have done it. There was no reason to do it for what purpose so I did not.
Micah Loewinger: I've gotten you to admit that you're corruptible.
Nasir Memon: Well, we all can be. Let's put it that way.
Micah Loewinger: I don't really know how useful ENF analysis is for mass surveillance. There are far better ways to track people, like GPS or the type of stuff you can legally buy from data brokers -- even, little visual clues in the back of a selfie can lead a dedicated sleuth to figure out where you live. What drew me to learn more about ENF is the poetry of it. I mean think about it: [sounds] Every time you turn on a light or plug in your phone or vacuum your rug or blow dry your hair...you are contributing to the “ever-so-slightly-wiggle” as the grid adjusts itself to our needs. It's a barely audible symphony that we’re all playing a part in.
[music]
Micah Loewinger: The American electrical grid (which has been called “the largest machine in the world” is a pulsating map that should remind us of just how interconnected we all are. Coming up, our final mystery is about another map made of sound… that no human, not even Jen Munson, can hear. This is On the Media.
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