Audio Evidence Forensics: Finding Signals In The Noise

The Value of Audio in Proving Your Case

TASA ID: 14235

I listen for a living. Since childhood, sound has always been something I naturally paid close attention to. It began with the reflective environment of my small stone Catholic Church I grew up in. It began with my fascination with the bell tower that I often got to ring. It began with hearing my own voice booming out from the balcony over the congregation without any amplification whatsoever. Not only was I fascinated with what the sound was, but the dissonant harmonic reflections it produced as it blanketed and bounced through a stereo field, how it would sustain, how it would decay and then release. In modern audio production, we call that Attack, Sustain, Decay, Release (ASDR). I was fascinated with everything, not just music but foley, from ocean waves, to 4th of July fireworks and everything in between. By the time I actually began engineering sound, I already had a lifetime of developing my best set of tools, my ears.

As an adult, my love for the rule of law, integrity and justice led me to work with law enforcement, national security organizations, and attorneys. Sound productions, like cases, can be enormous puzzles to put together. Combining the two became possible when the field of audiology, welcomed with open arms, the modern music production software and hardware, making forensics accessible to consumers. Digital audio software technology swiftly grew with powerful software applications designed by devoted, brilliant engineers. Incredible tools for the manipulation of sound files improved over time in accuracy and reliability. Global competition drove innovation, open and shared instruction, and the exchange of ideas was liberating. The modern sound community emerged. The designers made these tools affordable as it was for the greater good of the public sound support community. In fact, the tools are so powerful, this analyst submits there isn't anything audio producers can imagine that cannot be created and built. Big recording studios took a hit and the era of the independent art and commerce producer came to life.

For those of us who live and breathe sound technology, we went into film production toiling away over how to make what we saw on the screen come to life. I have personally spent countless hours working on screaming, gunshots, wind, rain, farm animals, creating monsters, robots, you name it. The right sound at the right time, in the right place, and traveling in the right direction in the environment.

I was asked to do some videography for an attorney who wanted to take many depositions but budget challenges limited the case to no more than two with a court reporter and a videographer. It just was not the justice that was deserved. We went to work taking depositions with just myself as the deposition officer, my digital camera and field recording gear. We took all the depositions we needed and if we wanted a transcript, then we crossed that bridge when the time came, and that is how I got into forensics. I decided I could use my skills to help solve crimes and save attorneys some money. My Berklee credentials got me into the Center for Media Forensics at the University of Denver's forensic program and under the instruction of audiologists and pioneers of the Audio Engineering Society, the first authority of audio. My instructor was Romanian with a very thick accent that kept our attention every tic of a second. It was like being with the League of Extraordinary Gentlemen. We came from Italy, France, Los Angeles, Canada, and me from Austin, all there to study sound science and forensics applications. Having been an engineer, knee deep in the analysis and processing of frequencies already, I was no stranger to spectrum analysis, hardware components, whatever it was. The terminology was no problem; and as a legal professional, affidavits and report writing were quite familiar.

Additionally, I knew I could assist law enforcement achieve better body cam recordings. Do law enforcement officers, now responsible for recordings and the chain of custody, have time for a huge learning curve of audio science? Not likely. Many have a hard time using their police car amplification properly so that they can be heard clearly several yards away. Gain structure is not something a typical police officer thinks about, but if you don't set it properly, there goes the audio. Cell phone users do not consider or learn about filters, surround sound apps, RF line level buzzes, or that they should stop tapping their pencil on the table during an interview or go outside if in a noisy restaurant. How many times have important recordings been masked because the recordist did not take into consideration loud broadband environmental noise or obnoxious machine tones during an interview? Quite often.

Modern forensic and audio production tools can be very effective in repair and enhancement if it can be done. If a jury can hear recorded dialog so clearly to determine inflections of a voice, the breathing, the tone, then the emotion on tape makes for a far greater impact on the listener. Enhancement can be beneficial to bring out background noise revealing other evidence as well which is not considered as an edit.

Authentication of recorded audio can verify event consistency and the chain of custody. For example, are the time codes consistent with the length of the original event as testified to in deposition or discovery? Is there evidence of tampering after the original recording was made?

The ear development, experience, and skill of the engineer are paramount to identifying sounds present in the recording, such as a dragging or scraping noise, machine tones, ambient broadband noise, or even if a barking dog is outside or inside for example.

In short, the job of the audio forensics expert is the science only. We do not determine the intent of the recordist nor the intent of the parties captured on the recording. Just the science of what the audio itself reveals. The chain of custody is documented and basic information on the media data itself such as the recording device used and the generation of the evidence. The software applications and formats are documented through running computer forensic scans of the audio for identification. Ultimately, the steps used to enhance or to analyze recordings can be reproduced by another qualified forensics expert to verify the reported results. The data says what it says. Audio evidence can be a crucial and reliable component to your case.

TASA Article Disclaimer

This article discusses issues of general interest and does not give any specific legal or business advice pertaining to any specific circumstances.  Before acting upon any of its information, you should obtain appropriate advice from a lawyer or other qualified professional.

This article may not be duplicated, altered, distributed, saved, incorporated into another document or website, or otherwise modified without the permission of TASA and the author (TASA ID #: 14235) Contact marketing@tasanet.com for any questions.

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