Myths, promises, and realities

If only it were true, as the televised CSI seems to promise, that any audio recording could be made intelligible with a little bing from a computer. The realities of forensic audio may surprise you—amazing things are possible, but not all things.

As forensic audio engineers, sometimes we can make out words in what sounds like a totally unintelligible digital hash. We can often filter the sound of the airplane out enough to hear the drug deal going down. We can make out the whisper recorded in the squad car and hear a suspect ask his friend, “Where’d you hide the gun?” We might even be able to unearth information on an 18-minute gap in a recording, or uncover what Rodney King was really saying. We can have an opinion on whether or not a voice belongs to Osama Bin Laden. We can test to see if a recording is edited, even if it is a digital file. And very soon, we may be able to discover what date, time, and where a recording was made—after the fact—from almost any recording, even ones from the past.

What a forensic audio examiner cannot do is alter the laws of physics. The covert recording made with a cheap digital recorder, set on the longest record time, and hidden way underneath the bed may very well yield an enigma that will be impossible to decipher. Numerous times, I have been paid good money to try to enhance an important recording after the FBI or another very competent forensic audio lab has already had a whack. Detectives can’t believe that key words cannot be deciphered. No matter how much you complain that you saw it on TV, if the information isn’t there, it can’t be unearthed.

Forensic Audio Investigation
In my forensic audio practice in Los Angeles, I perform several types of investigation. The most common is audio enhancement. I take a recording in whatever format it comes in and enhance the audio to improve intelligibility. There is a big difference between “listenability” and “intelligibility.” Listenability refers to how “nice” or “good” a recording sounds. I am capable of improving music, for example, by removing pops, distortion, etc. but my goal is usually to be able to understand the words, even if the resulting sound is brittle and hard on the ears. For this I use some rather expensive computer equipment and specialized forensic audio programs.

In particular, covert recordings present a number of challenges to the forensic audio engineer since a detective frequently faces problems that he cannot control. Suspects whisper, end up far from the microphone, and often speak with an accent or in “code.” Recording situations are rarely optimal. For this reason, it is best to at least have a high-quality, uncompressed recording made using a good recorder with good microphones, even if they are very tiny ones.

Another major kind of examination is one of authenticity. The question is whether a recording is authentic—typically meaning continuous, not altered or edited. There is a specialized form of “tape authentication” where an examiner uses the characteristics of the recorder used and examines the audio tape physically under a microscope using a magnetic developing solution. This is a very time consuming process and only applies to tape recordings.