Audio Forensics: What We Hear v. What We Record
By: David Smith
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In Audio Forensics, it often comes down to ears versus microphones. In one corner, we have the human ear with all its amazing capabilities. In the other corner, the fantastic piece of technology known as the microphone, with its ability to record sound to a digital file or tape for later playback.
Ears and Microphones are Different
While not a bold statement of Audio Forensics, it is, however, an essential statement as many tend to believe that they are the same.
Real World Example One:
You're at a party, and you find yourself captivated by a person speaking while standing halfway across the room. Even though that person is some distance away from you, you are still able to look at her and determine most, if not all, of what she is saying.
After the party, you're sent a video that was shot at the occasion. You remember the man with the smartphone making the video from about where you were standing. The engaging speaker LOOKS the same but now SOUNDS completely different from what you remember
While you remember hearing the scintillating remarks of that certain partygoer, the audio on the video serves up a smorgasbord of party chatter from many different people.
Real World Example Two:
An attorney contacted me and asked if I could perform a Forensic Audio Authentication Analysis on a recording. The attorney's client claimed that his voice had been recorded at another time and inserted into the audio in question.
The client was the former husband of a woman accusing him of making a threat, allegedly when he returned their child after a weekend visitation. There were two specific provisions in the court order regarding the child's transfer:
- The exchange had to occur in the daytime in a well-populated public place; and
- The ex-wife had to use a small handheld digital recorder to record all of their meetings during the exchange.
The attorney's client told me that, since his client was aware that everything he said was being recorded, he would never have threatened his ex-wife during the exchange. He also contended that she had waited almost a full day to report the threat to police, an action she would have taken immediately had there been an actual threat.
While not denying that the recording contained a threat, his client further contended that the extra day had given his ex-wife opportunity to insert the threat into the original recording.
The Forensic Authentication
After completing the Forensic Audio Authentication and Examination, I determined that the recording was continuous and unaltered. What she claimed that he said, he actually had said during the normal recording. But, although the authenticity of the recording had been settled, the question remained, "Why didn't she hear him when he said it?"
Now the parties heard the threat on the recording and only disagreed on when and how it got there. They also heard that it was spoken at a lower volume level that the rest of the conversation. One possible explanation was that he said it softer because he wanted her to hear it and didn't think that the recorder would pick up his voice at almost a whisper.
In reality, something very different had occurred. The ex-wife, so focused on the child during the custody exchange, did not hear the whispered threat when it was spoken. She didn't hear it until the next day when, free from any distraction, she played back the recording for the first time. The digital recorder's microphone, without the very human issue of distraction, had recorded everything, including the whisper.
Our sensitive ears, powerful brain, and amazing auditory systems work together to allow us to focus on something of interest. We tune-in to that subject, sometimes to the exclusion of other sounds around us.
But microphones typically pick up everything in front of them. They have no ability to selectively tune-in or tune-out certain sounds as we can. Microphones make non-subjective recordings of all sounds within range.
And in Audio Forensics that is the difference between what we hear versus what we record.
David A. Smith, ACFEI, IEEE, AES, has more than two decades of professional experience with audio enhancement. Experienced in criminal and civil cases including murder, corporate fraud, employment discrimination, sexual harassment, labor, and family law. Mr. Smith can consult with counsel offering audio forensic evidence examination, analysis, litigation support, expert advice, expert testimony, and related expert witness services including preparation of cross-examinations and courtroom presentations. Clients include Prosecutors, Defense Attorneys, Family Law & General Practice Attorneys, other Legal and Investigative Professionals, HR Depts., Corporations, Private Detectives, & Individuals.
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