Forensic Audio Enhancement

What is Forensic Audio Enhancement?

Forensic Audio Enhancement is the process of clarifying audio recordings to increase intelligibility. This is done through various processing techniques to remove unwanted noises like static, HVAC fans, hums and other distracting noises from the recording and increase the desired sound. The “Forensic” component to forensic audio enhancement is the scientific approach to enhancing a recording. There are many situations where forensic audio enhancement helps reveal the events or conversations as they occurred. Primeau Forensics understands the importance of evidence integrity. The techniques we use are accepted in the scientific community and all work products that we provide are accurate representations of the events as they occurred. We carefully document every investigation so that our work product is ready to be submitted into evidence.

The Forensic Approach

When the enhancement is done from a forensic perspective, the processes applied are done with a systematic approach that preserves the evidence integrity  as well as admissibility into court. Often times when a lay person makes adjustments to a recording in an attempt to increase the ineligibility of the recording, they may make changes to the recording which makes it an inaccurate representation of the events and inadmissible to a trier of fact A qualified forensic expert must perform the forensic audio enhancement investigation, document the procedures used, and present their work product in order for a trier of fact to admit it as evidence. Edward Primeau has been practicing audio and video forensics for over 30 years as an audio expert witness.

 

TYPES OF RECORDINGS

We examine a variety of audio evidence recordings including but not limited to; recordings made on smart phones, deposition video, digital handheld recorder, digital pocket recorder, cassette tape, micro & mini cassette tape, law enforcement dash cam, 911 dispatch, courtroom recording, confidential informant, wire tap, voice mails and many more.

PRELIMINARY ANALYSIS

In order to determine how successful the forensic audio enhancement investigation will be, our experts require that all recordings be preliminary examined to determine the success rate of the forensic audio enhancement investigation.   At Primeau Forensics, we call this a preliminary analysis or investigation. The preliminary analysis includes basic enhancements to audio recordings and video recordings that contain audio evidence. In addition, our experts will help you understand the significance of the recording and how it pertains to your investigation as a whole.

CRITICAL LISTENING

No two audio recordings are exactly the same, and therefore there is no one way to perform a forensic audio enhancement investigation. When I first receive an audio recording from a client, I begin my forensic audio enhancement process by listening through the recording multiple times. This process helps us to identify the specific issues of the audio recording so we can address them with individual enhancement accuracy.

Critical listening is key for identifying different sections and dialogue of the recording. When I refer to sections, I mean portions of the audio that have different characteristics such as levels, frequency ranges, or signal to noise ratios. For example, the first section may have two people talking quietly with a lot of street and car noise in the background. The next section may have a more audible conversation with a train passing far off in the distance. The third section may have no background noise at all but the lower frequencies of the people talking are suddenly louder. Each section of the audio recording has different characteristics and will need different processes to correctly enhance them.

FORENSIC AUDIO ENHANCEMENT SCIENCE

Understanding the different tools used in both analogue and digital audio editing laid a strong foundation for my career as an audio forensic expert. For example, what audio enhancement tool should I begin with? What order should I apply the processors to acquire the best results?  Should I start with noise reduction or equalization? Is compression or normalization more applicable to this audio recording? These are important questions to consider when beginning the enhancement process. The plugins I use are based on the critical issues I hear in each section. The order of the processors can be key in producing a clean and balanced work product.

Typically noise reduction will be the first step in the structured approach. This prevents the noise from becoming an issue in further processing. Compression will usually be applied next to raise and balance the level of the section or overall recording.  Equalization can now be applied to the less noisy, balanced signal. Gates and further compression can also help remove unwanted sound or boost desired sound. While this is a good structure to follow, it may not be right for every situation. If there is an exceptional amount of background noise, a gate can be helpful before most of the other processors, especially compression. Occasionally equalization is also better as the first executed process. By drastically cutting a small range of frequencies, unwanted overtones in the human voice can be removed from further processing. Each recording can require any number of processors to reach the desired results; in some cases I may add as many as ten different plugins before I am satisfied with the results.  

 

 

 

 

 

 

 

 

 

Some examples of processing techniques include but are not limited to the following:

  • NOISE REDUCTION
  • LOUDNESS ADJUSTMENTS
  • DYNAMICS PROCESSING (COMPRESSION & LIMITING)
  • MULTI-BAND COMPRESSION
  • EQUALIZATION
  • NOTCH FILTERING
  • DE-CLICKING
  • DE-CLIPPING
  • DE-CRACKLE
  • DE-REVERB
  • DE-PLOSIVE

COURTROOM USE

The problem then becomes maintaining a chain of custody. If your recordings are to be used in court, establishing a chain of custody is extremely important. It does not look good to the other side when you use a software program yourself. This is why most people in need of audio enhancement seek assistance with a company like Primeau Forensics.  Not only do we enhance audio and establish a chain of custody, we also create a forensic transcript when necessary that is signed and certified by an audio forensic expert. This forensic transcript is then used with the enhanced audio evidence to create a packaged piece of evidence that is more powerful than the enhanced audio alone.

If you have an audio recording that you question or need help understanding, please give me a call for a pro bono conversation. I apply my forensic expertise to cases in the United States and many countries around the globe. Any and all formats of audio and video accepted. Retainer agreement available on request; travel expenses will be quoted in advance excluding meal expenses and flat rate time for travel instead of hourly.

Click HERE to email your questions or

Call 800-647-4281 in the USA or +01-248-853-4091 Internationally.

Ed Primeau’s Curriculum Vitae has several references which include cases he has testified in as well as clients he has worked for in these cases.