Posts Tagged ‘audio forensic expert’

Three Tips on Testifying from an Audio Forensic Expert’s Perspective

Thursday, March 31st, 2016

The Importance of TestifyingAfter 34 years as an audio forensic expert testifying in dozens of cases on the local State and Federal court levels, I have gained experience and knowledge about the trial process.

Today, more than ever, many of my cases go to trial. Fewer criminal cases take a plea offer and even fewer civil cases settle outside the court room. I am spending more and more time helping courts understand audio evidence.

I chose to write about my court room experiences because I am often asked about testifying by our clients. Testifying is a very important aspect of my profession.

First off, testifying in court requires extensive attention to detail – both expected and unexpected. Testifying as an audio forensic expert requires an enhanced mental clarity, as the medium of audio may be interpreted subjectively, as well as objectively. My testimony as an audio forensic expert must be clear and precise, as well as simplified. It must include science, as well as opinions. It must also help the trier of fact understand the audio evidence for their decision making process. One excellent trial lawyer I previously worked with put it this way; I tell what is real and what is fake.

Tip #1-‘Preparation-The Key to Successful Testimony’

One of the most important elements of testifying is preparation. I always over prepare and insist our client attorneys schedule time with me before I get on the plane and in person before entering the court room to prep for trial. You can never be too prepared.

My preparation includes reviewing all work products, notes, reports and other expert depositions before going under oath. I also learn the client lawyer’s trial strategy and my role in that strategy. Preparation also includes anticipating cross examination.

Last November, I testified for the Attorney General for the State of New York in a negligent homicide in front of two Grand Juries. I had an agenda for preparation but my client lawyer had an even more intense preparation planned. We prepped my testimony for almost 8 hours over two days. There were 30 defendants and 8 defense lawyers. Since we anticipated cross there were no questions at all from any of the lawyers! Each one stood up and spoke (said) ‘No questions your honor’. Why? Because we did a great job preparing and anticipating cross; we brought out all questions on direct.

Tip #2-‘Look like an expert’

One of the most crucial aspects of testifying is the expert’s appearance. First impressions are extremely important especially when you are going to testify in court in front of a judge, jury and opposing counsel. Your credibility is directly proportionate to the way you look. Unfortunately, in a professional environment such as a courtroom, pre-conceived judgment from the jury is more than likely to happen. You want to make the best, most professional ‘first impression’ possible. Forensic experts need to look conservative. Some lawyers will not retain a forensic expert with visible tattoos, piercings or radical haircuts.

I remember testifying in Boston a few years back. Our trial team had two other experts one of whom I never would have guessed was going to testify. He did not wear a tie, his hair was a mess and his clothing was ill-fitting. I am not picking on this expert, but rather giving you a vision of what NOT to look like when testifying. On one hand, I shouldn’t be so judgmental, on the other hand, this is what a judge and jury do; judge!

Experts are paid well for their expertise; they should look the part.

Tip #3-‘Communicate with Conviction’

High quality communication is another ingredient to the success of your testimony. Not only does your communication matter for trial lawyers, but also your ability to communicate your findings to the jury is just as (if not more) important. When answering questions under oath, I keep my answers short and to the point and resist the temptation to ramble on. I include scientific terms in my answers but make sure to simplify them if a juror’s body language implies confusion. Communicating with conviction also requires great eye contact. When answering questions, I always begin my eye contact with the person who asked the question. Then while continuing to answer, I make eye contact with the rest of the court room including the jury, judge and opposing council. One major mistake I often see experts make is answering questions with tunnel vision, staring only at the person asking the questions. It’s not a deal breaker but will reduce the impact of your words and testimony.

Testifying as an audio forensic expert about forensic audio enhancement can be difficult due to the potentially low court room acoustics and environment typically found in most court rooms. Enhanced audio evidence is perceived when played in the court room. The problem with playing audio in the court room there is no visual representation of what the audio is portraying. It is important that everyone in the court can hear and comprehend your audio evidence. This too is communication. Equally important is that your testimony has to be crystal clear in helping guide the jury to understand your science and opinions.

Forensic Transcripts

I often include a forensic transcript as part of my work product.  A forensic transcript is created by me using critical listening skills I have developed over 34 years practicing as an audio forensic expert. It ends with a paragraph like this: ‘Based on the pains and penalties of perjury I testify that the above forensic transcript was prepared by me and is an accurate representation of the events as they occurred at the time of recording so help me.’ Then I sign it and notarize if necessary.

Aside from these three tips, I focus on a healthy mindset. I make sure to get plenty of rest the night before. I drink a lot of water and eat healthy. A healthy mind set will contribute to a successful testimony. Testifying is stressful, but the key to success is preparation, appearance, and communication.

How to Set Up a Microphone for CCTV Systems

Tuesday, March 10th, 2015

CCTVClosed circuit television systems have become a major contributor of evidence to court cases. While the video from these systems is often very important, the audio can often play just as much of a role in the investigation. At Primeau Forensics, we often are hired to enhance not only the video from a CCTV system, but the audio as well. As an audio forensic expert we are qualified to perform forensic audio enhancement.

Clients typically hire us for enhancements because the original CCTV system was not set up properly and was capturing less than ideal quality audio and video. Many times, the audio is more valuable than the video because of what was said during the event. While enhancing the audio is possible, setting the microphone on the system correctly can be extremely beneficial when an incident does occur. Getting a good, clean signal from a microphone relies on two key principles: microphone gain and microphone placement.

Setting a proper gain structure for a microphone will always yield the best result for any kind of recording. Gain is applied to microphones because microphones have inherently low levels. A preamp is used to amplify the signal before it is recorded into a system. When setting the gain, the goal is to get a high enough level that the signal is audible, while also making sure that the level does not clip the system or preamp. Clipping means that the signal has exceeded the capabilities of the system and begins to distort. This distortion hurts the quality of the audio and can make it very difficult to understand what people are saying in a recording.

Gain structure is often set based on the input signal, which makes setting a surveillance system microphone difficult. The input signal of a surveillance system is always changing and cannot be manually reset whenever people enter or leave the area. When setting the gain for a surveillance system microphone, it is usually a good idea to test different levels of sound in the room. Having someone talk or even yell in the room while you set the level can ensure that the recording will not clip when it is recording later on.

We recently recovered some surveillance video evidence that required an audio enhancement. When we received the audio, we found that the gain had been set too high and the entire recording had clipped. We also found that because the room was small and filled entirely with hard surfaces, there was a buildup of reverberant sound. Reverb consists of reflections of sound off of surrounding surfaces. Some reverb is always present, but too much can begin to cover up the direct sound. Direct sound is the original sound coming directly from the source, such as a person speaking. In this case, the gain should have been set much lower on the microphone. This would have produced a much cleaner and more audible recording. Reverb is a more difficult issue to combat and relies much more on the microphone placement.

Different microphones will have different pickup patterns, which means that they will pick up sound in different directional patterns. Typical microphones used for surveillance systems are either cardioid or omni-directional microphones. Cardioid microphones pick up sound from one direction and reject sound from the opposite direction. Omni-directional microphones pick up sound from all directions. Knowing what kind of microphone your system is using is the first step to setting up a microphone. If you are using a directional microphone, it should be aimed at the area where the sound sources will be. Omni-directional microphones are easier to set up because they do not need to be aimed in any direction.

When placing the microphone, it is important to be aware of other extraneous noises in the room. We often see CCTV systems placed near the ceiling and in corners so they can obtain the best view point of the area. This is not always the best location for the microphone depending on how the room is designed. If an air vent or another electrical device is near the microphone, they will add a large amount of noise to the recording and can cover up desired sound. If a directional microphone is being used, try aiming the rejection end of the microphone at the unwanted sound source. This means the least amount of the unwanted signal will be picked up.

Reverb can also be an issue in smaller spaces that have no absorptive surfaces. When the direct sound is buried by the reverb, it can make the desired signal muddy and undefined. Acoustic treatment can be added to a room to deaden the amount of reverb, but this is more often an approach for musical spaces. A typical fix for a surveillance system can be placing the microphone closer to the desired sound. Placing the microphone in the center of the ceiling instead of in a corner could cause the microphone to pick up more of the direct sound, resulting in better and clearer audio. Because sound and reverb tends to build up more in corners, placing the microphone away from the corner will also prevent it from picking up those extra reflections.

Audio evidence is a very prominent part of many investigations and court cases. Setting up a microphone properly for a surveillance system can often make a huge impact on whether that audio can be used as evidence or not. As an audio forensic expert, I come across many audio recordings that could have been much more audible if the system had been set up properly. When installing a surveillance system, setting the gain for the microphone and placing the microphone properly will always improve the quality of the recorded audio.

Blindspot – How to Make Digital Audio Recordings for Evidence

Thursday, February 19th, 2015

audio recordingsAs an Audio Forensic Expert, my day to day activity includes forensic services like audio enhancement and authentication, as well as voice identification. Audio enhancement is probably the most common service I provide, because more often than not, the audio evidence was not recorded in the best way possible. Audio evidence can often be one of the most important pieces of evidence for a case, so it should always be given a great deal of attention.

One of the most common ways people create digital audio evidence is by using digital audio recorders. Law enforcement will often use them for interrogations and confessions, and sometimes even out in the field as a backup for their dash cam or body cam. People outside of law enforcement use them for creating audio evidence as well.

I would like to mention that concealed audio recordings are not always legal. Federal law states that creating an audio recording only requires one person’s consent, but some states follow a ‘two-party consent’ law. This law means that all parties who are on the recording must give permission to the person recording in order for it to be used as evidence in court. I highly suggest looking in to your own state’s laws regarding concealed audio recordings before making one.

When creating a digital audio recording that is going to be used in court, there are many things one should be aware of before making the actual recording. The biggest issue I usually come across is low recording levels. While it is possible to increase the signal level afterwards through forensic audio enhancement, this is unnecessary time and money spent. This will also increase the noise floor of the recording, which can make it more difficult to hear what is happening in the recording. Creating a clean and audible original recording can make the enhancement process much easier and can often make the evidence much more useable in court.

When preparing to make an audio recording, regardless of whether it is a concealed recording or an interrogation recording, the user should always look at the settings of the digital audio recorder.

Two major settings determine the quality of a digital audio recording: sample rate and bit depth. Together, these settings also determine the bit rate of a recording. Changing these settings will affect both the quality of the audio recording and the amount of space used on the digital recorder. When creating digital audio evidence, it is necessary to balance these two in order to get a high quality recording while optimizing the amount of space on the digital recorder. Thankfully, many digital audio recorders will record in lossy compressed formats like MP3 files, which take up much less space and don’t sacrifice a lot of quality.

When recording digital audio in an MP3 file format, the two key settings to pay attention to are the sample rate and the bit rate. The sample rate will ultimately determine the range of frequencies the recorder picks up. At least two samples are needed to record any frequency, which means the sample rate must be twice as high as the highest frequency you need to record.

The range of human hearing is roughly between 20Hz and 20kHz. Typical audio recordings are done at 44.1kHz to capture the full range of human hearing. While this is standard for music and other professional recordings, it is not always necessary for audio evidence.

Most fundamental frequencies of the voice are between 100 and 500Hz with some of the most important harmonic content between 1kHz and 4kHz. This means that a sample rate as low as 8kHz can sometimes be adequate for recording a conversation, which will also save a large amount of space on the digital recorder.

Bit rate determines the amount of bits that are processed per second, which determines the fidelity of the audio. Typical MP3 files are recorded between 192kbps (kilobits per second) and 320kbps, but they can be as low as 32kbps. Just like with the sample rate, a higher bit rate means a higher quality of audio but also a larger file size. The issue that arises with low bit rates is that the compression process applied to the file can start creating digital noise in the recording. This digital noise can often cover up parts of the recording and once it is there, it is very difficult to remove.

When determining what settings to use on a digital recorder, it is always a good idea to make multiple test recordings before making an audio recording that will be used as evidence. These test recordings will let you try out the various settings and then listen back to see what sounds best and what fits your needs the most.

Another setting that is sometimes included on digital recorders is the ‘voice activation’ setting. This setting will start and stop the recording based on the amount of signal the microphone is picking up. While it can be a good way to save space on the recorder, it is not recommended that this setting be used when creating any kind of digital audio evidence. If this setting is on, the digital recorder could stop recording at a key moment in the conversation and miss a crucial piece of evidence. If extra space is needed on the digital recorder, adjusting the quality settings is a much better way to go. Recording all of the content at a slightly lower quality is a lot safer than relying on the ‘voice activation’ setting and missing important content.

Monitoring the battery life on the digital recorder is another very important thing to keep in mind. In some applications, like recording an interrogation, the digital audio recorder can simply be plugged into the wall so it will not run out of power. In other cases where you do not have this option, make sure the battery is fully charged or you have put in new, good quality batteries. Keeping extra batteries with you is also good practice, just in case the recorder does run out of battery and needs a replacement.

When creating the actual recording, try to be as close as possible to the person being recorded. As I mentioned before, one of the biggest issues with audio evidence is a low volume or record signal level. The farther away from the source the microphone is, the lower the signal level and the lower the signal to noise ratio. This means that less of the desired signal and more of the unwanted background noise will be recorded. Background noise can include any extraneous sounds such as furnaces, refrigerators, air conditioners, televisions or even the internal sound created by the digital recorder itself. These sounds can detract from the quality of the recording and often make the desired signals unintelligible.

Placing the digital recorder in a good location is key for making a good digital audio recording. Keep a few things in mind when making your recording. First, the microphone should always be aimed at the subject that you are recording. When placing the recorder in a pocket or a purse, aim the microphone towards the subject. Also make sure that the digital recorder is relatively stable in its location, because any movement of the recorder will be picked up by the microphone and can cover up other parts of the recording. Pay attention to any materials that may be in between the microphone and the sound source; the thicker the material, the more damping there will be on the signal, which will decrease the record level.

Many digital audio recorders have a microphone input which allows you to use an external microphone. The external microphone is always the best option to use if the recorder is going to be placed inside something. When using this option, it is always a good idea to use a high quality external microphone.

There are many different types of microphones that will work better for different situations. Lavaliere microphones are extremely helpful because they are small and usually omnidirectional. This means that they will pick up sounds from all directions and they can be placed anywhere on your person while the digital recorder stays in your purse or pocket. Other microphones, such as directional microphones, may work better during police interrogations because the subject will not be moving during the recording.

As I mentioned before, always create a test recording before making the recording that will be used as evidence. Testing different microphones, microphone placements and locations will help you learn how your digital recorder works and responds to different environments. If possible, try conducting the test recording in the same place that you will create the real audio evidence so you can prepare for any extraneous background noises and other obstacles. After making the test recordings, listen back so that you can make sure the desired sounds can be heard and the sound quality is high enough.


Eavesdropping: Is It Worth The Risk?

Thursday, August 15th, 2013

eavesdroppingYou’re having problems at home.  Your spouse has been acting very suspicious recently. You can’t help but think that your significant other is having an affair, but lack of communication with that person makes it impossible to find out the truth.  In a desperate attempt to find out what’s really going on when you’re not around, you decide to set up audio recorders all throughout your house to use for possible audio evidence against your spouse.

This is a practice we see every so often at Primeau Forensics. We’ve received a handful of cases in which a third party requests an analysis of audio taken from digital surveillance of a private conversation. What these people don’t realize is that these actions are against Michigan’s eavesdropping/surveillance laws (laws vary from state to state). The consequences of eavesdropping on a private conversation are dire, and can lead to not only a considerable fine, but also possible jail-time.  Before we dig deeper into this subject, we must ask the question: What exactly constitutes “eavesdropping?”

The surveillance and eavesdropping statutes are determined at a state level. Some states enforce what’s known as “one party consent.” Basically, as long as one side of the private discourse agrees to surveillance of the conversation, the action is legal.  Here is a guide of which states enforce one party consent and which states enforce two party consent.

According to Michigan State Law, eavesdropping is defined as “to overhear, record, amplify, or transmit any part of a private discourse of others without the permission of all people involved in the discourse.” In other words, the person doing the eavesdropping must have consent from both parties to record the private conversation.  This is what’s known as “two party consent.”

You might be thinking, “But this is my home! I have the right to dictate privacy in my own home!” This is also not true.  Michigan State law defines a “private place” as “a place where one may reasonably expect to be safe from casual or hostile intrusion or surveillance but does not include a place to which the public or substantial group of the public has access.”  This includes an empty home. As long as the location is not somewhere the public can easily get to, it’s considered a private place.  So yes, it is even illegal to eavesdrop in your own home.

In the state of Michigan, eavesdropping is considered a felony.  The potential  consequences of these actions include imprisonment in a state penitentiary for up to 2 years, a fine of up to $2,000, or any combination of both.  Obviously, this does not include the potential fines you’d face if the violated parties request a civil case.

In case the purpose of the blogpost hasn’t become clear by now, the point is that eavesdropping is very illegal, and the consequences are very serious.  Even if you do find some juicy inside secrets, Michigan law also states that “using or divulging any information which you know or reasonably should know was obtained in violation of the wiretapping laws” is strictly prohibited.  So if you suspect something is going on at home, the risks involved with eavesdropping just aren’t worth it.  Healthy communication with your spouse is a much safer option when issues at home arise.

photo credit: Eavesdropping ( Hello Hello anyone there ) via photopin (license)

Can’t Convict on Less Than 20 Words

Wednesday, February 22nd, 2012

less than 20 wordsSince I began my career as an audio forensic expert 28 years ago, I have been retained on two drug trafficking cases where the US prosecutors office was trying to convict based on five words spoken during a confidential informant recording.

I have been on both sides of the fence working for the state as well as for the defense. The scientific community, specifically the American Board of Recorded Evidence, explicitly states that in order for an audio forensic expert to deliver a positive identification, “At least 90% of all comparable words must be very similar aurally and spectrally, producing not less than twenty (20) matching words. The voice samples must not be more than six (6) years apart.

Voice identification is both an art and a science.  It is an art in that the forensic examiner has to conform best practices to each specific, unique case.  Not all voice identification cases are the same. In fact, I have had related situations but every case has still been unique.

I have identified singers, good guys and bad guys. I have testified in cases where my testimony was crucial in the outcome of the case.  One thing remains certain: a government body cannot convict because they believe a specific person said the phrase that their case is built around.

For example, imagine I am with three other friends and after a confidential informant approaches me inquiring about a crime we are plotting, one of us in the group says the “phrase that pays” in order for the CI to complete the sting. Unless that CI’s recording has a 20 or more word “phrase that pays” it’s technically their word against the defendants about who said the convicting phrase.

In other words, the difference between first degree murder and the death penalty vs. a lesser judgment could be that phrase spoken during the recording and the person who spoke that phrase on the CI recording.

An audio forensic expert has the ability to identify that voice by creating an exemplar and comparing at least 20 words, no fewer, spoken by the accused.  I recently had a case where the state was going for a more severe conviction based on five words spoken during a CI recording. However, it is not possible to deliver a positive identification based on so few words.

For more on Voice Identification, check out Ed Primeau’s latest book, “That’s Not My Voice!” available on Amazon.

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