Audio & Video Forensics
Submitted by admin on 12:26 am
Free consultation 800-647-4281
AUDIO AND VIDEO FORENSIC SERVICES*
AUDIO FORENSIC SERVICES*
- Background noise removal/sound clarification
- Voice ID and comparison
- Audio recording authentication
- Cassette format transfers micro, mini, standard
- Audio expert testimony
- Compact Disc reproduction
- Audio cassette duplication
- Accurate transcription services
For more information visit Audio Forensic Expert:
http://trueaudioforensics.blogspot.com/ for more Info
Bell Labs were the first to discover that spoken word patterns and sounds could be identified and characteristics applied to identify the individual who made them. This has been a very important advancement in forensic science because the potential to assist law enforcement is well worth the effort it takes to defend the proponents and practitioners.
This is an exacting science that has huge benefit to the courts. In this article, I will define in layman’s terms, the process, as I see it that is acceptable in the scientific community, of voice identification.
There are many cases I have worked on requiring the truth about the source of the threatening voice on the recording. There was a bomb threat called into 911 on the western side of my home state of Michigan. The call was made from a pay phone outside of a convenience store to 911. The caller identifies herself as an employee of XYZ Company. When the police arrive, they find the employee who identified herself to 911 operators. The employee denies making the call.
She is immediately charged with making a false bomb threat call. I am hired by the defense and prove through the procedures outlined below that his client did not make the call.
When comparing spoken word samples for the purpose of identification, the scientific community, state police crime labs, forensic experts and designers and developers of electronic (especially computer) equipment and testing software programs, requires the examination of every aspect of the words spoken. The words themselves, the way the words flow together, the pauses between the words, the way the words are formed by the mouth and larynx. The forensic expert must careful examine all scientific evidence and follow procedures.
These scientific procedures include:
1. You must establish that the quality of the recording in question is acceptable and workable. Sometimes, it may be necessary for the expert to apply some light equalization or other non destructive processing to reduce or remove background noise. At the same time, make sure the sample is long enough to conduct the testing. In my opinion, this is a sample longer than thirty seconds.
In another case I was retained to examine a telephone answering machine one word recording. I was asked by the defense to listen to the one word voice mail and see if I could do anything to help. I insisted that there was not enough spoken word to compare and test. This is where the case got interesting. His client had been violated of his parole and put back in jail because the recipient of the call whose machine made the recording insisted it was the defense. The court listened and put the defendant in jail. Obviously, my job was to convince the court this was unacceptable in the scientific community and could not be proven.
2. Visual examination of the original recording. This includes physical characteristics of the tape or digital recorder. You must examine the cassette or other tape source to determine if there are visual signs of tampering or alteration.
3. Visual examination of the sound wave, sonogram and spectrograph. Once the recording has been visually inspected and no signs of tampering can be found, the recording is loaded into a computer and tested using software tools to tell about the recordings characteristics. This same process is applied to the exemplar to determine those characteristics using the same software.
4. Create an exemplar of the accused for comparison to the measurements taken from the evidence as outlined above. The speech must be the same as the speech on the evidence in order for the testing to be accurate. However, it is still possible to compare speech if the exemplar is of another origin or conversation.
5. Audio examination of the speech pattern, pronunciation, voice tone and inflection, accent, dialect and specific characteristics (like a lisp or significant â€œsâ€ delivery). There is a rhythm of how an individual speaks and regardless if trying to disguise speech for the exemplar, the rhythm still shows through. The expert must pay careful attention to the rhythm of spoken word formations. I listen to single words as well as phrases and sentences. Most always, I load in to my computer original evidence sections of spoken word recordings and edit exemplars back to back with the original sections. It is always helpful to then make a sub file of words within the section back to back with exemplars. I like to cut and paste the original / exemplar back to back samples so as to repeat the assembly over and over helping the auditory identification process. That way, your ear can experience the sounds, vowel formations and consonants without interruption.
There are a lot of character traits that can be experienced in a spoken word recording if you listen carefully. I have been working with professional speakers and other spoken word recordings since 1980. In those days, we would edit Â¼â€ reel to reel tape with razor blades to make a recording sound like it was recorded start to finish without a single mistake. Some of my edits were pretty tricky. I got so good I could split words in two and even three edits to fix a problem or shorten a script. When you do this enough, you get to understand the characteristics of speech patterns.
Another part of my then job was to, on occasion, have to re record a portion of speech on a different day from the same voice that made the recording and make it sound as if the revision never happened. I got quite good at this because it happened often and my job depended on it.
One project I had was a famous pizza chain had recorded several radio commercials with the tag, â€œWhen you make pizzas this goodâ€¦â€ which was grammatically incorrect. I had to go through over 100 voice takes and remove the â€œsâ€ so the producer could then select the take (s) they wanted to use in the commercial. It’s amazing what you can do when you put your mind to it. During this period and the following 25 plus years, I developed my critical listening skills which are a very important attribute in a voice identification expert.
When conducting the examination, not only do I look for similarities I also look for differences to help arrive at a conclusion (beyond a reasonable degree of professional certainty). These characteristics are evident in a persons voice even if they attempt to disguise their voice.
There can sometimes be differences in speech patterns that can help identify clues in your identification puzzle. I look for several similarities as well as differences, nasal resonance differences, voice tone with regard to inflection both similarities and differences.
After the investigation and testing procedures are complete, I arrive at one of the following conclusions. They are: positive identification, probable identification, positive elimination, possible elimination or inconclusive. The key is to have a methodology and standard procedure developed that you strictly follow every time you do a identification and comparison so your mind can follow along and the results are accepted in the scientific community and courts. This is my procedure that I follow when conducting voice identification.
For any questions or more information, call 800-647-4281 or email Ed@PrimeauProductions.com.
VIDEO FORENSIC SERVICES
- Video authentication
- Forensic video examination
- Video image clairification
- Video frame captures
- Video format conversion
- Video expert testimony
- Video duplication
- CD ROM design and programming
*Any and all formats of audio and video accepted.
Today, evidence from video recordings plays an increasingly significant role in the criminal justice process. It’s an example of the newer forms of evidence that law enforcement officials take into consideration when presenting facts in court cases.
Video footage from in-car mounted cameras in police cars, security cameras used for businesses, institutions, stores, etc. â€“ plus footage from private citizens â€“ is often surfacing as evidence in legal situations. Perhaps you have convinced your department head or company to install a surveillance system to monitor security situations and possibly detect instances of crime. And perhaps the camera/recorder has captured footage that may be key to a convicting a perpetrator. Unfortunately, during the â€œdiscoveryâ€ stage of the case, the defendant’s attorney states that something happened to the video recording; there is a glitch. He announces that a forensics expert is now on his defense team to prove that your video has been falsified and/or inadmissible.
This brief article covers video forensic examination tips that may keep your recordings glitch-free. If you are involved in video recordings that can be used for legal evidence, this article may save you from having your evidence challenged in court.
As an AV forensics expert, I’m often hired by law enforcement officials, attorneys and corporations to report on the methodology used in videos cited as legal evidence. As part of my work, I review many resources, like police chase footage, hidden-camera coverage from workplaces, retail store surveillance footage, and so on. The question I’m most often asked is to respond to is: â€œWas this video recording edited or altered in any way?â€
To respond to this, forensic experts must gather scientific clues to answer the following questions:
â€¢ What do we know about this recording to be true (within a reasonable degree of professional certainty)?
â€¢ On what type of equipment was the video recording made?
â€¢ Is the original recording of the video available for examination?
â€¢ Is the original recording equipment that made the tape also available for examination?
While extensive technology is certainly involved in the video recording process, and this article cannot begin to address it fully, here are theories/procedures regarding examination which provide an overview of how forensic experts may need to examine and identify video anomalies.
Anomalies are abnormalities, deviations or â€œbreaksâ€ in the recording process as evidenced on the physical tape or digital video file. These aberrations can impact the legitimacy of a video (digital or analogue) as a piece of legal evidence.
When a videotape recorder or digital video recorder (DVR)/video camera records to videotape or DVR, the recording process creates a very structured format of code and information that is embedded on the tape or hard drive to create pictures and sound and signals. (Note, all videotape, except Â¾â€ format video, travels from the left spool to the right spool when the machine is in the â€œRecord,â€ â€œPlaybackâ€ or â€œFast Forwardâ€ modes. DVR recordings store video signal on hard drives using proprietary codecs or code and compression).
Digital video requires a different forensic process than analogue. Instead of recording the video image on tape, digital video is recorded on computer hard drives or digital video recorders (DVR).
Video systems that record digital video have several variable settings like frame rate and recycle time. If you look at the video below, you will better understand the importance of frame rate and forensic examination. Some officials and owners of digital video systems choose a lower frame rate to save on hard drive storage space. This makes it difficult for the forensic examiner to authenticate and identify events in question on the video recording. It is more efficient and effective for closed circuit television (CCTV) owners or purchase additional hard drive storage instead of choose a low digital video frame rate.
There are also several manufactures of digital video CCTV systems making it necessary for the video forensic expert to review operators and installation manuals for each system. I have been certified by the Pelco Global Institure in digital video and understand the details of digital video systems and the processes necessary to investigate digital video surveillance footage.
On analogue tape, at the bottom of the tape (running just parallel to the tape edge) is the control track, or recording signature. Just above the control track is the composite picture and audio signal. On hi-fi VHS video recorders, above the composite signal, there are the hi-fi tracks. These are the physical areas of the recorded tape that forensic experts look at to determine if glitches â€“ or anomalies, as they are professionally termed â€“ exist.
There are two types of anomalies: non-destructive and destructive. A non-destructive anomaly is any deviation from the normal events one would expect to see and hear when viewing a videotape. In other words, a non-destructive anomaly or glitch in the tape could be an edit, an indication of a record interrupt or an over-record (recording over a previously recorded tape or segment of the tape).
When examining a tape for anomalies, the forensic expert must take all things into consideration. For this reason, it’s strongly recommended that the examination start by determining the origin of the recording device. If the machine that made the recording is available, a test recording â€“ or exemplar â€“ should be made using blank, unrecorded (virgin) tape. The goal here is to gather information on the alleged machine signatures from the original recording device used â€“ that is, signals from the control track and the stop and start signatures. This is done for comparison purposes and to identify facts that may exist about the anomaly.
Next the tape being examined â€“ i.e., the evidence or the alleged video containing the in-question anomaly â€“ is viewed in â€œPlayâ€ or â€œFast Forwardâ€ mode to determine the number of deviations or anomalies. Each deviation is carefully noted and examined using test equipment that helps to determine the characteristic of the anomaly. Much like the medical profession uses testing to research and document the reason for an illness, diagnostic tests are also necessary for forensics professionals; testing will eliminate certain factors so that real facts can be isolated to conclude, to a reasonable degree of professional certainty, the source or cause of the anomaly.
Many times it is necessary to physically examine the tape at the actual spot where the anomaly exists. An expert will physically examine the videotape itself to accomplish this, applying a special, non-destructive liquid to the tape which then develops the digital information so it can be reviewed. (This is much like how a photograph is developed, applying developer chemicals to the film.) Once the tape is â€œdeveloped,â€ the expert can continue with the physical examination processes.
For a jaunt back in history â€“ yes, in the â€œoldenâ€ days when I began my career â€“ video recording tape was not yet in plastic shells but rather on spools, making it fairly easy to physically review the tape; but it was also quite easy to damage the tape’s edges since the tape was a good deal more exposed to mishandling. Videotape edge damage is considered a â€œdestructive anomaly.â€ This damage can be in the form of a crease, tape crinkle, the result of a liquid spilled on the tape, etc. Of course, this can still occur with today’s videotape, even in the protective shell or tape housing, but not as easily.
Also, back then, videotape was comparatively more expensive than it is now. Thus, videotape was quite often recycled and recorded over for economy’s sake. As you might imagine, anomalies were fairly prevalent in those years. In one respect, this was good for my skills development as a forensics expert since I had the opportunity to experience dozens and dozens of destructive anomaly situations during the late â€˜70s, for instance. This permitted me to gain great insight into their cause and nature.
When videotape started to be enclosed in cassette-styled plastic housings as VCRs gained in popularity, it became a bit more difficult to physically examine tapes for anomalies. So the scientific community evolved accordingly and developed new ways of testing.
Once you understand the science of how video recording works, how recordings and devices can be distinguished from each other, you’ll have a better understanding of how to go about identifying anomalies. I encourage you to read up on today’s video technology to advance your knowledge.
(You may also wish to refer to another article, â€œForensics: Video Authentication Process,â€ included on this website.) Meantime, for simple practice in identifying anomalies, try creating your own:
Take a tape that has been previously recorded over. Fast forward the tape to about 10 minutes in and record something new, getting about 30-40 seconds’ worth. Rewind the tape and review your â€œover-recordâ€ characteristics. Take note of how the over-record starts and how it ends. These â€œin and outâ€ points are characteristic of the equipment on which you recorded the program.
Of course there are many other forensic aspects in the study of anomalies â€“examination of stop/start record â€œsignatures,â€ record-interrupt distances on the tape, study of the audio and video tracks, control track examination, application of magnetic tape developing fluid to further detect anomaly conditions â€“ to name key areas.
But getting back to what’s most likely your interest in uncovering reasons for an anomaly, this works down to two essential questions: Did it occur as a result of wishing to intentionally cover up something? How do we know it wasn’t an honest mistake? And finally: Can we recover the images and sounds of the previously recorded material?
The answer is no. Once original material has been recorded over, it’s gone forever. But, as mentioned, the machine control track, audio tracks, etc., can provide recording â€œsignaturesâ€ that exist on the physical tape; these may contain the clues toward determining others certain â€œtruthsâ€ about the over-record. Our article on â€œVideo Authentication Processâ€ provides added information on these points.
When dealing with a video recording device and tapes that may be needed to substantiate legal situations: Make sure your equipment is cleaned and well-maintained and do not use videotape that has been recorded on previously. Use a new tape.
With the main investment already made in video equipment, the slight cost and effort to maintain that equipment â€“ and the nominal cost of fresh tape stock for all recordings â€“ is well spent. Having a clear recording on new tape stock (which avoids pre-existent anomalies that would exist on recycled tape) is an inexpensive way to better ensure your videotape evidence is solid and will be less apt to be court-challenged for authenticity.