From de facto sound, you're listening to 20,000 Hertz. The stories behind the world's

most recognizable and interesting sounds. I'm Dallas Taylor. This is the story of how

audio can be key to solving a crime.

Forensic audio is the use of audio evidence and the investigation of a crime or for use in

a court of law. And the clip you just heard was from Malaysia Airlines Flight 370, the one

that went missing in March 2014, somewhere near the Southern Indian Ocean. Investigators found

some debris in January 2017 that they have identified as being part of the plane. But to this day,

no one really knows what happened. When these final recordings between the pilots of the missing

Malaysian jet and their air traffic controllers were released and appeared to have been edited,

NBC News turned to Kent Gibson for analysis. I'm a forensic audio and video examiner and I've been

in the business about 30 years. I do authentication, which is is this recording edited or inauthentic in

any way? He determined that the audio had been edited in at least three places. Listen carefully

to the following clips for words that have been cut off. He was also convinced that this

section had been recorded through a speaker or microphone.

The tape may have come from multiple sources. Listen to it back to back with another section of the tape.

And now the part that sounds like it was recorded through a speaker.

It's entirely possible that this is either a case of the Malaysian authorities editing the tape

because parts of it contain information that the government didn't want shared with the world,

or the tape was poorly put together from multiple recordings of the same thing. Regardless,

maybe this evidence, along with other findings, will someday help add to the bigger picture of the case.

Kent does a lot of authentication cases like this one. Some of this work relies on tech and some

on good old-fashioned listening. There are a lot of software ways, there are a lot of

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