Christopher Brooks, LEED, AP, Acoustic Expert

Computer reconstruction is a powerful tool for visualizing situations such as accidents or crime scenes.  But these models are typically limited to sight—missing sound: a crucial component of the multi-dimensional experience of reality.

Incorporating audio into visual models can significantly enhance their perceived realism and provide critical insights that visuals alone cannot capture.  For instance, in accidents involving a truck backing up onto a victim or a person walking backward into machinery, the key question becomes: could the victim have heard the danger in time to avoid injury?  Or, if a gunshot is involved, could the location of the gunshot be clearly perceived?

While sound level measurements provide useful data, they offer one-dimensional information in our inherently three-dimensional world.  By utilizing binaural recording techniques and mounting specialized microphones directly in a person’s ears, acoustic experts capture a more realistic auditory experience by replicating how audio is perceived through two ears. 

At times, the recording itself, without a visual computer model, can yield clarifying information.  To demonstrate, here are two recordings using this technique.  Listen with headphones for the full effect.

Standing across the street from a person operating a leaf blower, as several cars pass by:

In a backyard with a fountain.  Note how clearly one can hear the locations of the birds:

Sound level meters and reference source sounds are utilized to calibrate binaural recordings to ensure the sound level in the listeners’ ears provides a realistic representation of what an individual would have heard in a specific situation.  A dummy head designed to be used with specialized microphones may also be used for instances where it would be difficult or too dangerous to place an actual person in that position.  When appropriate, binaural recordings may also be captured in motion, such as while walking along a particular path. 

In one case, an acoustic expert was asked to take recordings of a truck backing up to the victim’s location.  This required positioning a person in a safe location while inclining their head (equipped with the microphones) as close to the victim’s location as possible.  In the audio recording captured through this process, the truck is completely indistinguishable from other background noise until the moment of impact.

These recordings can then be synchronized with computer reconstructions, offering a more complete recreation of the incident.  When presented to a jury, these synchronized audio-visual reconstructions—played back through headphones—can provide an accurate, immersive, and scientifically grounded experience of the event.

Christopher Brooks, LEED, AP, Acoustic Expert with DJS Associates, Inc., can be reached via email at experts@forensicDJS.com or via phone at 215-659-2010.

Categories: Environmental

Tags: Audio-Visual | Binaural Recordings