'Audio forensics' helps solve crime through the sound of gunshots

American company ShotSpotter has created technology that detects gunshots using microphones placed around neighbourhoods. While automating this process is new, using audio to investigate crimes involving guns is not.

Rob Maher is a professor of electrical and computer engineering at Montana State University who specializes in audio analysis. Maher is often called by police to study audio files and determine where a gun was fired.

Maher, speaking to Spark host Nora Young, said that the prevalence of recording devices—from phone cameras or security cameras—means that when gunshots happen, it's common to have an audio recording. From that, he can precisely gauge the time between events, such as who shot first, or how many seconds passed between someone saying something and a shot.

The math behind how ShotSpotter technology works—by measuring the time it takes the sound to reach each microphone, it can estimate the original location—is well-established, according to Maher.

But the technology has other limitations. 

"There may not be a direct line of sight from the shooting location to the microphone," Maher said.

"They may be behind a building or down an alley...and so the signal picked up from the microphone may not be a direct sound. It may be a reflection, or a sound that has been diffracted around the corner of a building. So that will lead to some uncertainty.