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Los Angeles Times & Ted Rall: Forensic Video Response

Friday, September 11th, 2015

I was hired by the LA Times to perform a forensic audio investigation on a 2001 recording of a jaywalking citation being given to Ted Rall. The LA Times posted my results in an recent article to clarify the reasons behind Ted Rall’s dismissal from the paper. Ted Rall has since posted a rebuttal to this article on his blog, in which he made various claims about the results of my investigation. I would like to clear any confusion or misinterpretations about my forensic investigation and the results it produced. In the list below I have outlined points which I believe address the issues Mr. Rall published in his article:

  • I did not hear a crowd of people on the audio recording that I enhanced of former Los Angeles Times freelancer Ted Rall being ticketed by an officer for jaywalking.  I heard two people other than Rall and the officer talking on the recording.  At most, I could make out the word “jaywalking” being spoken by one of the two people.  I did not hear anything about “handcuffs” on Rall’s enhanced version of the recording or on the version that I enhanced.
  • We have an established chain of custody of this recording by the Los Angeles Police Department since officer Willie Durr recorded it in 2001.
  • We have no signs of tampering anywhere in the recording.  I found no evidence of tampering when I performed my authentication test.
I have created the following video to clear up these misunderstandings as well as clarify the actual results of my investigation.

Audio Authentication and Visual Inspection

Tuesday, April 21st, 2015

visual inspectionAudio Authentication and Visual Inspection

Sound waves can tell us a lot about a recording. Like metadata, the visual elements of a sound wave can expose characteristics of an audio recording without even having to listen to it. These characteristics can be important, especially when it comes to detecting edits within audio evidence. The process of observing these characteristics is called visual inspection. This is a part of audio authentication process.

Visual inspection (a general term that comprises a variety of forensic tests like narrow band spectrum analysis) is a crucial part of an Audio Forensic Expert’s job. To understand how crucial visual inspection really is, it’s important to understand the concept and value of the noise floor.

The noise floor (usually unwanted sound) of a recording is the present background noise and overall “ambience” of a recording. For example, if you’re recording yourself speaking on the street in New York City, and you’re speaking into a microphone while standing in one place, the sound of the cars going by, the conversations happening around you, and the overall city noise (unwanted sound) will contribute to the noise floor.

If you’re standing in one spot recording that audio, the noise floor will never change, because the environment your audio device is picking up will stay consistent the entire time. The second that noise floor is altered;you know you have an edit.

There are many ways to examine this. One of the most reliable ways to observe this noise floor is what’s known as a spectrogram. The spectrogram is meant to read the spectrum of an audio recording. To put it simply, a spectrogram takes the contents of an audio recording and conforms the characteristics to blends of color that represent the spectrum of an audio recording in Hz. You can see that below.

Now, because the noise floor of a recording never changes, you can tell when you have an edit when the spectrogram shows a change in, or absence of, color. The noise floor will always stay consistent, so when there’s a short drastic change such as the one pictured below, you know you have an edit. This makes the recording inauthentic.

Spectrogram edit circled

Surely there are other ways to visually detect edits. Even the sound wave itself can expose an edit.

All sound waves should be smooth and continuous. Even if someone were to loudly clap during an audio recording, the sound wave will still remain smooth and continuous. When you see gaps, or a wave that is not smooth and continuous with another piece of the audio file, you know you have an edit.

Though a critical ear is generally considered the most important part of Audio Forensics, a good eye for edits in visual inspection can teach you a substantial amount about the evidence you’re working with before even taking the time to listen to it. Visual inspection really comes in handy when trying to determine the authenticity of a piece of audio evidence and to make sure a proper chain of custody was kept throughout the distribution of audio evidence.

Knowing Your Digital Audio Recorder

Thursday, December 18th, 2014

digital audio recorderWith digital audio recorders, there are a lot of options when it comes to the quality of the audio recording. Despite the easy access to these options, they are often overlooked. People are either unaware of these settings, or simply forget to check them when they begin a recording. While most settings on a digital recorder will yield a good enough quality recording, I have come across digital recorders with very low quality settings that could result in very distorted or unintelligible recordings. If you are using a digital audio recorder, it is important to have a basic understanding of what contributes to the quality of your audio recording.

Two major settings to be aware of are the sample rate and the bit depth of your recording. The sample rate determines how often a sample is taken from an incoming waveform. The bit depth determines the number of bits for each one of these samples. Together, these settings and the number of channels will determine what the bitrate is. The bitrate is how many bits are processed per a period of time. Bitrate plays a bigger part in lossy audio files.

Sample Rate

There are a few standard sample rates used in most recorders, often including 44.1kHz, 48kHz, and 96kHz. Audio is usually recorded at 44.kHz to capture the full range of human hearing. An audio waveform has a positive and negative pressure area; therefore a minimum of two samples must be taken from a frequency to reproduce it. The range of human hearing is generally given as 20Hz to 20kHz, though it can vary depending on the person. With a sample rate of 44.1kHz, frequencies as high as 22kHz can be recorded, which more than covers the average person’s hearing range. Higher frequency ranges such as 96kHz are used to capture twice as many samples and therefore create a higher quality recording, though most would argue that it is almost impossible to hear any quality difference unless using professional audio equipment.

Bit Depth

The bit depth, as mentioned, determines the resolution of each sample that is taken. A 16 or 24 bit setting is most commonly used; depending on what medium is being used. Audio CD’s, for example, only use 16-bit audio. The bit depth will determine the signal to noise ratio of a recording depending on a logarithmic formula. The signal to noise ratio is the comparison of the desired signal to background and internal noise. A 16-bit recording will have a 96dB signal to noise ratio, while a 24-bit recording will have a 144dB ratio. While 24-bit does have a higher SNR, the 96dB range of a 16-bit recording is often more than enough to create a good quality recording.

Bitrate

When using a format such as an MP3, bit depth no longer applies because of the lossy compression format. This is when bitrate becomes a more important factor of a recording. The bitrate is the number of bits processed in an amount of time, typically written in kilobits per second. The bitrate of an uncompressed audio file, such as a .WAV file, can be determined from the bit depth, sample rate, and number of channels. A CD with 44.1kHz, 16-bit stereo audio has a bitrate of 1411kbps. MP3 and other lossy audio files typically have much lower bitrates, which is why they are so much smaller than uncompressed formats. They achieve this through perceptual coding, which essentially removes parts of the data that are found to be unnecessary and unperceivable by the human ear. Typical MP3 music files have bitrates between 192kbps and 320kbps in order to maintain good quality. Digital recorders that record lossy formats will often have optional bitrates as low as 32kbps.

When choosing what settings to use for a recording, it’s important to consider the purpose of the recording. Music production is usually done with at least a 44.1kHz sample rate and a 16-bit depth. WAV and AIFF files are typically the file formats used for the master recording. When later compressed to MP3, as mentioned before, a bitrate between 192kbps and 320kbps is used to maintain the highest quality possible after compression. When a digital recorder is being used for another purpose, such as recording a conversation, other settings may optimize the performance and memory of the unit while still maintaining a high enough quality.

Whenever a smaller sample rate, bit depth or bitrate is used, the recording will always take up less space on the memory of the recorder. This can be very important to someone who may need to leave the recorder on for long periods of time. When capturing audio evidence, a recorder may need to be left on for hours or even days. If this is the case, and a lower quality file needs to be used, it is important to know how to go about maintaining quality while optimizing the memory.

Options and Limitations

While the range of human hearing covers up to 20kHz, fundamental frequencies of voice do not fall in the higher end of the frequency range. The human voice is strongest in the 1kHz to 4kHz frequency range. Because of this, it is possible to capture a completely audible and intelligible recording of people talking with a sample rate of only 22kHz. This would mean the highest frequency recorded would be 11kHz, which is still much higher than the most important frequencies in the voice. Some recorders can even be set to an 8kHz sample rate. While this does save a lot of space on the recorder, this means the cut off frequency would be 4kHz. This may be acceptable for some applications but may also cut down on the clarity of the voices. When a large amount of background noise is present, the higher frequencies between 4kHz and 10kHz can add some needed clarity to the voices. It is always a good idea to test the different sample rates before using them to make sure that the quality will be adequate for its purpose.

When trying to optimize the memory on a digital recorder, it is almost always a good idea to use a lossy compression format, such as an MP3. This means that determining the bitrate rather than the bit depth will be a factor in the size of the recording. As mentioned before, a bitrate between 192kbps and 320kbps is often very good quality for an MP3. When recording only a voice in which the content of the recording rather than perfect quality is the concern, lowering the bitrate can be very helpful for conserving space. One should be cautious when lowering the bitrate because the data compression may begin to affect the intelligibility of the recording. When too much compression is introduced, digital noise become easier to hear, which can sometimes cover up the desired signal. I have heard 32kbps recordings that had so much added digital noise that the much of the conversation in the recording had become unintelligible.

In summary, digital audio quality is determined by its sample rate and bit depth or bitrate. There are many options for these settings and not all of them may result in a good quality recording. It is always important to check these settings and be aware of the limitations each setting comes with before beginning a recording. Take into account the content of what you are recording and the quality of audio that is needed. The better you know your digital recorder, the more effective it becomes.

 

Authentication of Digital Audio Recordings

Tuesday, November 11th, 2014

How to tell if an audio recording has been edited?

When one of the parties in a litigation believes that an audio recording was tampered with or edited, an audio forensic expert is brought in to investigate the recording. When we authenticate an audio recording, the first step is to establish chain of custody. While it is the first step, chain of custody does not, in and of itself, establish a recording as being authentic. I have seen audio evidence that was not authentic and was stored in a digital audio recorder.

A majority of audio recordings we are hired to authenticate are created on digital audio recorders or smartphones using a recording app. These devices are easily concealed in a pocket or purse. They come in many shapes and sizes. They record various formats. One of the first steps an audio forensic expert must take when authenticating a digital audio recording is to become familiar with the equipment that created the recording.

So why is audio authentication so important? What should an audio forensic expert be aware of when examining audio evidence? What is the process of examining and authenticating audio evidence? I am going to answer these questions and more in the following post.

Importance of Audio Authentication

The authentication process determines whether or not the audio recording in question has been tampered with. In this age of digital audio, edits can be made and covered up very easily. There are free versions of audio editing software – such as Audacity – which are available on line and can make edits that alter the events or conversation that originally occurred in digital audio recordings.

If audio evidence is found to be altered, it should be ruled inadmissible in court because it is not an accurate representation of the events that occurred.

So what should the audio forensic expert be aware of during the authentication process?

First, establish and determine the chain of custody. If the expert is able to retrieve the evidence from the original source, in most cases that will automatically create and establish an authentic chain of custody. Or, provide clues of tampering if the recording was edited and re recorded. If it’s not possible for the forensic expert to retrieve the recording, then the forensic expert must carefully go through all of the documents and reports that arrived with the evidence.

Sometimes a chain of custody log from law enforcement will be included, which will strengthen the authenticity of the audio evidence. But if the chain of custody cannot be established, the forensic examiner must rely on other techniques as well as their own expertise to determine the authenticity of the evidence. If further investigation reveals more inconsistencies in the recording and metadata, more often than not that recording is determined to be altered.

Digital audio recorders aren’t the only equipment that record audio evidence. CCTV surveillance systems, as well as most other digital video recorders, will include both audio and video in the recordings. As an Audio and Video Forensic Expert, I often work with both the video and audio from these recordings.

When I receive digital media evidence that includes sight and sound, I analyze both audio and video using separate forensic processes. I have come across cases in which the video was unedited but the audio had been tampered with. In this case, I was unable to authenticate the evidence because a chain of custody could not be established. Plus, there were anomalies in the audio that could be measured, heard and documented.

Critical Listening

Observation

One of the first steps that I take when audio evidence arrives at our lab, I listen critically to the entire recording a number of times. During this process I note unusual sounding sections in the recording which are called anomalies. I take notes and place markers using the forensic software so that I can find them later and include them in my forensic report.

These unusual sounding sections can be changes in the background ambiance, inconsistent speech pacing and wording as well as changes in the noise floor. The noise floor is a series of natural and electronic sounds that should be consistent throughout the recording. Noise is defined as any sound source signals like hiss, hums, wind, HVAC and other sounds that are not part of the intended recording.

The Listening Space

It’s important for the forensic expert to examine recordings in a quiet, isolated room during critical listening so as to avoid any outside disturbances. The quiet environment enhances the critical listening focus. High quality, professional grade monitoring headphones and high quality studio monitors (speakers) are best for critical listening analysis of digital audio recordings.

Professional grade headphones and monitoring speakers will have the most accurate frequency response, which means they produce neutral and natural sound. This is very important for the forensic expert because subtle boosts and cuts in frequencies can impact the analysis of the digital audio recording.

Sometimes frequencies may be more audible in headphones and sound clearer to the forensic expert while other frequencies may be better heard through speakers. When the forensic expert is examining audio evidence for authentication, it is important to use both headphones and speakers to hear every aspect of the recording.

In some audio evidence I have examined, I have been able to hear a second noise floor in the recording. This usually occurs when a recording is played through speakers or an auxiliary cable into another recorder. The original noise floor from the recording is heard along with the second noise floor created from the second recording.

Electronic Measurement

audition-eq-analysis

After critical listening, the forensic expert must use electronic measurement to examine the audio evidence. This is done by noting the prominent frequencies in the voices or other sound source and the noise floor. The levels of the recording and of the different frequencies can be measured as well.

Tools such as spectrograms, frequency analysis windows and level meters are very helpful for observing and collecting this information. The expert should note the frequency range of the overall recording, the voices or conversation and the noise floor or extraneous sounds in the recording.

If the frequency range of a voice suddenly becomes larger or smaller or shifts in frequency range, that can be a sign of an edit. Sudden, unexplained changes in the noise floor level as well as the sudden presence of another background noise can also be a sign of an edit. As I mentioned before, I have come across recordings in which I could hear two noise floors. This can often be measured and seen in a spectrogram and a frequency analysis panel.

Visual Inspection

wavesurfer-and-izotope

Visually inspecting the audio wave form and spectrogram is the next step in authenticating the audio. This goes hand in hand with the electronic measurement as the forensic expert analyzes the physical wave properties and frequency information. Waveforms are continuous and smooth when examined very closely.

Even an abrupt, loud sound like a clap will have a smooth, continuous wave. If there are sudden breaks in the waveform of a recording, these are signs of editing. The expert should also pay close attention to the phasing of the waveform. This can also been seen when visually zooming in to the waveform. If the waveform of the recording is suddenly inverted, this can also mean an edit was made.

The spectrogram will display the full frequency spectrum with warmer or colder colors representing the strength of that frequency. The noise floor can be seen very clearly in this view, helping to identify breaks in the sound. All recordings have some noise floor, even if they are almost inaudible. When viewing the spectrogram, any breaks in the noise floor may be signs of an edit. Changes in the volume of the noise floor can also be a sign of an edit.

Analyzing Metadata in Digital Audio Evidence

When I first began working as an Audio Forensic Expert, most of my work was with analog audio evidence in the form of mini, micro and standard audio cassettes. I did have some cases where reel to reel tape was used.

Today almost all recordings are recorded digitally and there is important information from the recording process that must be analyzed when performing an audio authentication. Digital audio recordings contain digital information which reveals information about how the recording was made and the type of equipment that created the recording.

This digital information includes Meta Data, EXIF (exchangeable image file format) data as well as Hexidecimal data. If a recording was loaded into a software program capable of performing edits, there will often be a footprint left in the recording HEX information showing what software was used.

When examining the digital information, it is necessary to create an exemplar recording to compare the metadata with the original. An exemplar is a recording that is made in conditions that are as close to the original recording as possible, which include the same equipment and recording environment. Using this exemplar, the forensic expert can compare the metadata and HEX information of the two files. If there are inconsistencies in the data, that can also be a sign of tampering.

For a forensic expert to authenticate a piece of audio evidence, the expert must prove beyond any doubt that the recording is in its original form and has not undergone any tampering. If a piece of evidence is not authentic, it should not be used in court because it may be incomplete or altered to purport events that did not occur.

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.

Audio Anomalies Discovered on Video Evidence

Tuesday, March 26th, 2013

audio anomalies Audio Anomalies Discovered on Video Evidence

One of the activities of an audio forensic expert is to determine whether or not an audio recording has been altered or edited when it has been submitted to be used in the courtroom. As an audio forensic expert I find, very often, that when people are in shock or in the middle of a traumatic experience they remember the series of events differently than they actually occurred. Therefore, people involved in a legal case may believe that a piece of recorded evidence has been altered when, in fact, it has not.

Many times defendants will tell me that they said something during a police interrogation that has ‘magically’ disappeared from the interrogation recording. I find it hard to believe that a police officer that has so much invested in their career, may be close to retirement, would risk their reputation, career, credibility and retirement to alter an audio recording in an effort to wrongfully convict someone.

But, when someone who is in a litigation or has been convicted of a crime feels that a recording has been altered the audio forensic expert, like myself, comes in to authenticate the recording.

Today nearly all audio recordings are created on a digital recording device. This same principle holds true with digital video recordings that have audio recording capability, such as, dashcam video from police cars that have a microphone on the officer as well as a microphone in the car. Smartphone video also records audio in addition to video. One of the activities that I am starting to notice as an audio forensic expert is that audio tracks are being altered in smartphone recordings and video portions of those recordings have not been altered. That’s why it’s very important for the audio forensic expert to authenticate both the audio and video portions of those recordings.

I was working on a case the other day that was recorded on an iPhone and while looking through the vector scope and the other tools that I use to authenticate audio and video evidence I noticed on my oscilloscope that there were anomalies in the audio recording. I went back to review and there were no edits in the video, but there were in the audio. It was clearly heard, using my critical listening skills, as well as viewed on the oscilloscope. The spectrum of that audio was not authentic.

I could not establish a chain of custody and the file had been downloaded from the iPhone into a computer and burned onto a disk. The original phone was no longer available and the file properties that were on the file that I examined did not match the file properties that an iPhone would produce.

Now we have a situation where I could not authenticate that video recording to be used in the courtroom because of the anomalies that I discovered, the file properties that had been changed, and the original phone that was not available for examination. When I draft my report for this investigation I list all of the reasons using scientific proof and keeping the report simple enough for the lay person to understand, explaining all of the reasons why this evidence should not be used in the courtroom because it is believed to not be the actual representation of the events as they occurred, based on the following reasons. Then I list all of the reasons, in order, as to what happened, when it happened and why it has altered the original evidence.

This report alone often helps litigators determine whether or not to use that video evidence. Because the bottom line is, there may be portions of that recording that aren’t altered. Let’s say from four minutes to six minutes it’s a complete piece of recording; at four minutes there’s an edit, a part was removed, and at six minutes there’s an edit, a part that was removed. But for that two minute stretch there are no edits or anomalies and there are words exchanged, video documented, that is still crucial to the case. A judge will look at that and say even though this recording has been altered the expert has said that two minute section is genuine and that’s very important to the case, and the judge will allow that portion of the recording as evidence in the case.

As an audio and video forensic expert, I examine both audio and video portions of video recordings and often times find anomalies or edits in the audio portion that does not occur in the video portion. It’s important for the forensic expert to list all of the anomalies, time coordinates where the anomalies occurred and the type of anomalies so that the litigators understand and can strategize how to use this information going forward to either prosecute or defend the case.

Release or Destroy Audio Evidence After Litigation

Wednesday, January 16th, 2013

audio evidenceAn audio forensic expert listens to audio recordings of litigation points during a forensic investigation. Oftentimes, these audio recordings are very sensitive in nature. They are crucial to the litigation and must be destroyed or returned to their provider once the litigation is complete. Generally, in civil litigations, settlements are reached based on a series of conditions. One of those conditions is often that all of the evidence be destroyed that was used to process that litigation. It is very important that the audio forensic expert stay in good communication with their lawyer contact to make sure that they clearly understand what to do with the audio evidence once the litigation is complete.

If that audio evidence were to become available to the wrong people after the litigation settlement it could violate and have other ramifications to the terms and conditions of the settlement. That’s why it is very important for the forensic examiner to know what is expected of them from the attorney and other litigators regarding that forensic evidence.

In the past I’ve received letters from attorneys asking me to dispose of the audio evidence I used to investigate their case. In my professional opinion, there are only two options for an audio forensic expert for dealing with the evidence they examined upon reaching a settlement in the litigation.

One, return the evidence back to the attorney or your contact person in the case. Signature required, delivery confirmation is essential so that the forensic expert has proof that it was returned to the appropriate party. Second, destroying the evidence by physically breaking or destroying the playing surface on a compact disc, which is the most common media for delivering the audio recordings to be examined by the forensic expert. Or delete files stored in computer hard drives or other external storage devices, such as a thumb drive.

So, we either return the evidence to the contact person, signature required so that we have confirmation and proof of delivery; or we dispose of the evidence by destroying the compact disc or delete from external storage device. It is best, if possible, to get their instructions in writing (particularly if the instructions are to destroy the evidence), just to protect yourself and make sure all your bases are covered.

I recently had a case that settled and I was contacted by someone who identified himself as a friend of one of the litigators, and claimed to have permission to listen to part of the audio recording that I investigated for this litigation. I denied the (alleged) friend access to the recording and contacted the party who retained me for the investigation and let them know I was being contacted. The huge problem here is that, had I given the audio evidence to the person that contacted me not only could I have jeopardized my reputation in the forensic community if this person had released that evidence, it would also have had a huge ramification on the settlement for my client because, that audio evidence being compromised, would also violate the conditions of his litigation settlement (not to mention opening myself up to a possible lawsuit for releasing the audio evidence to an unauthorized party).

Bottom line, when the forensic expert completes a forensic examination, it is the forensic examiner’s responsibility to determine what to do with the evidence that they have investigated so that it does not fall into the wrong hands and violate the terms of the litigation settlement.

photo credit: Salat via photopin (license)

The Why and How of Audio Evidence Integrity

Thursday, August 16th, 2012

audio evidence integrityWhen audio recordings are used in any litigation, the integrity of the evidence is not only important, but oftentimes questioned. It’s crucial to consider evidence integrity before you present your evidence in court.

As an audio forensic expert, I am often asked to authenticate audio evidence for litigations. This authentication process provides integrity for the audio evidence and strengthens its weight in the litigation.

For example, it is easy for just about anyone who has some basic computer skills to alter audio evidence by removing portions of the recording that they don’t want the litigators to hear. Although this is not a common practice, it has a huge impact on the credibility of the audio evidence being presented. The reason is as simple as this: the altered audio recording is not an actual representation of the facts as they occurred. Portions of the actual evidence have been removed.

This is similar to missing evidence from a crime scene. What if a police officer arrived at a crime scene and began moving or removing items from the scene? How would the crime scene investigation team know the actual facts of the crime as it occurred without all the evidentiary items at the scene?

Once the integrity of the evidence has been compromised, the audio component of the litigation is reduced to “he said, she said” – my word against theirs.

Police officers have been trained to maintain evidence integrity at the scene of the crime. However, people who submit media evidence like audio and video recordings may not completely understand how important it is to maintain evidence integrity.

Tips to maintain integrity:

1: Keep originals in a safe place.

2: Photograph or video record any specific activity information.

3: Retain a forensic expert to help you document the authenticity of your evidence.

photo credit: Scope via photopin (license)

Tips on Using Digital Voice Recorders in Litigation

Wednesday, August 15th, 2012

digital recorderPeople are using audio evidence in legal proceedings more than ever before in the history of litigation. Our electronic society involves many recording devices such as:

  • Voice mail
  • Smart phones
  • Digital voice recorders

Because these devices are so affordable and readily available, victims of unlawful acts in civil and criminal litigation have turned to digital voice recorders to capture conversations and use those recordings in court to bring out the truth of the disagreement or dispute.

Before you begin recording your conversation for court, keep in mind these very important facts:

  1. Make sure you are part of the recording. It is a violation of eavesdropping laws to hide an audio recording device anywhere – including your own home – and record any conversation that you are not a part of.
  2. Try to have your conversation outside of a restaurant or coffee shop environment. I have worked on many audio clarification cases that required serious work to enable a listener to hear the voices engaged in the conversation.
  3. Use digital recording equipment with built-in microphones, remotes or smart phones. Better microphones make it easier to authenticate the evidence because you can keep the original on the recorder.
  4. Always keep original recordings so they can be authenticated.

By following the four guidelines above, you can present the court with authentic recordings that have been made lawfully.

Maintaining Audio Evidence Integrity

Tuesday, June 5th, 2012

evidenceThroughout the course of my professional career, the necessity to maintain the integrity and the chain of custody of the original evidence has never changed. As a forensic expert, I am often asked to authenticate and clarify audio evidence that is not original, and that does not have a chain of custody that has been maintained. When working for defendants, I make it a point to bring this out in my reports and in my testimony. I often find challenging audio evidence containing anomalies or inconsistencies when conducting my forensic examination.

When I work for government agencies and police departments, I guide them through the process of maintaining integrity and a proper chain of custody on audio and video evidence. In fact, I have recently had several cases that involved audio clarification for different police departments.

Frequently, clarification of in-car video or audio tracks simply requires separating the radio chatter from the officer’s microphone. There are a couple of ways that I can do that as a forensic expert. First, in many cases, the radio chatter is on a separate audio track. I load the in-car video in its entirety into my forensic computer and then remove the audio tracks and work on them in Sound Forge to remove the radio chatter. This helps the prosecutor learn more about the audio portion of what went down and why that is important to the case. Other times, I apply compression and equalization to help remove unwanted noise and bring out the speech. Lastly, I lay that audio track back onto the video and export a new digital video file in an mpeg format so that it can be burned to a DVD. This process does not change the integrity of the evidence and my forensic documentation contains of all of the steps that I took so that I can maintain the chain of custody on the evidence as well as its integrity. This processes that I use is acceptable in the scientific community as well.

In litigation, sometimes the small facts about a video or audio recording are important. When those facts are difficult to see or hear, police departments and other litigators look to an audio forensic expert to help them better understand portions of a recording that are not as clear as was hoped when the recording was made. It could be because of wind noise, background cars passing by on the highway, or distortion from a microphone transmitter.

There are a number of things that can distort an audio recording, but a forensic expert can use multiple techniques to help restore the audio so we can better understand the facts as they occurred. A forensic expert’s role in litigation is very important. As an expert, he or she can help courts interpret the process of exporting the original evidence from the digital recorders, the chain of custody and the purpose of the processes that were applied to the evidence to help restore both sound and vision. Finally, a forensic expert presents these processes and the evidence in court–keeping it easy for the court to understand the facts as they occurred.

Ed Primeau Audio Interview on The People Speak

Friday, April 6th, 2012
Audio Forensic Expert Ed PrimeauThe shooting of Trayvon Martin took place on February 26, 2012, in Sanford, Florida. Trayvon Martin was an unarmed, 17-year-old African American male who was shot and killed by 28-year-old George Zimmerman, a man of mixed ethnicity (Peruvian and white American). Martin was walking from a convenience store to the home of his father’s girlfriend when Zimmerman, a community watch coordinator, began following Martin and called the Sanford Police Department to say he witnessed suspicious behavior. Soon afterward, there was a confrontation that ended when Zimmerman fatally shot Martin. Zimmerman described the shooting to the police who arrived on the scene as self-defense. Responding officers handcuffed Zimmerman and took him into custody but they did not formally arrest him, saying that they did not find evidence to contradict his assertion of self-defense. The lead homicide investigator was not convinced by Zimmerman’s account and wanted to charge him with manslaughter, but the state attorney’s office said there was insufficient evidence for a conviction. Both Martin and Zimmerman made phone calls during the incident, some of which were recorded.

http://www.thepeoplespeakradio.net/?s=ed+primeau

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