BLOG

Knowing Your Digital Audio Recorder

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

November 11th, 2014

AuthenticationOne of our day to day activities as audio forensic experts is authenticating digital audio evidence. 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. 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.

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

Importance of 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.

In the last 30 days, of all the audio authentication cases I was assigned, I found two had been edited. Both of the recordings were downloaded to a computer, edited, then played back and re-recorded through desktop computer speakers using a digital audio recorder. Most of the time, if an audio recording is edited after downloading to a computer and before authoring a CD, the editing can be detected in the digital recordings meta data. During the forensic authentication process, the software that created the edits will be detected in the HEX information of that edited recording.

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 a 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.

Process of Examining and Authenticating Audio Evidence: Critical Listening

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 ambience, 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.

Critical listening must be the first step to become familiar with the audio evidence. If an edit is discovered during the critical listening phase, they are usually in the form of abrupt changes. Detecting these changes is not easy and comes with experience.

It’s important for the forensic expert to put themselves 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 quality headphones and speakers will have the flattest 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

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

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 a quick, 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 show 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 done digitally, there is additional information that can be analyzed when performing an audio authentication. Digital audio recordings contain metadata which reveals information about how the recording was made and the type of equipment that created the recording. 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 . The exemplar is made on the same kind of audio recorder and, if possible, the same 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.

Hopefully this post helped inform you about the authentication of digital audio recordings. If you have any questions, email us at primeauforensics@gmail.com, or give us a call at 800-647-4291.

New Audio Recording on Michael Brown Shooting: Real or Fake?

August 26th, 2014
I was contacted today by two media outlets regarding an audio recording that was released last night to CNN. The recording is alledged to be a video chat with the gunshots that killed Michael Brown in the background.

I began my forensic investigation by researching the weapon Officer Wilson used to kill Michael Brown. The weapon is a Sig Sauer P229. Next I found a video on YouTube of the Sig Sauer P229 being fired. When conducting forensic comparison, I conclude the weapon in the recording matches the Sig Sauer P229. However, there are other much bigger issues.

Why did this person wait so long to release this recording? You would think he would go to authorities immediately! Next, why did we receive only a portion of an obviously longer recording? Then there is the fact that it sounds like he is reading instead of conversing with his girlfriend like he said he was? Plus, don’t you think he would stop when he hears gunshots? I know I would. Why does he continue to read right through the shots fired?

Seems like a fake recording to me. Something to get attention the day after Michael Brown was laid to rest. Don’t you think the timing is odd for this recording to be released?

Listen for yourself and let me know what you think. Let’s use #MichaelBrownAudio for discussing on Twitter.

 

Audio clip: Adobe Flash Player (version 9 or above) is required to play this audio clip. Download the latest version here. You also need to have JavaScript enabled in your browser.

The Structured Approach to Objective Audio Enhancement

July 9th, 2014

audio_waveformThe audio enhancement processes that I have learned are some of the accomplishments of which I am most proud as a forensic expert. Audio enhancement is both an art and a science; and as an audio forensic expert with 30 years of experience, I can tell you with confidence that no two assignments are the same. This knowledge has helped me develop a structured approach to objective audio enhancement.

In the following post I would like to help you better understand proper audio enhancement techniques through an objective and structured approach. On average, I enhance between 200 and 300 audio recordings per year. For each assignment, I use the knowledge and skills I have gained from past experiences to effectively enhance the recording. I believe I have developed a strong understanding and talent for audio enhancement.

When I first receive an audio recording from a client, I begin my enhancement process by listening through the recording several times. Critical listening is key for identifying different sections 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.

Most audio editing software allows you to add a marker to the timeline based on your cursor’s current location. During playback, using a hotkey relative to the software, I can add markers while listening through the recording in order to identify the in and out of each section. This can ensure that I do not use a processor that may hinder other portions of the audio. Once the sections have been established, I can apply different plugins to each section as needed. 

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 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.  

Many of our clients at Primeau Forensics will say that they attempted to enhance their audio recording on their own and were unsuccessful. I explain that the audio enhancement process requires experience as well as a structured, scientific approach in order to produce effective results. Audio editing software is only a tool used in the enhancement process and owning a program does not give you the experience and skills necessary to enhance audio recordings like a professional.  

The structured approach to objective audio enhancement comes from experience. It is based on years of ‘hands on’ work with audio enhancement as well as observing sound recordings and the critical issues that interfere with the desired sounds. Please contact Primeau Forensics for your free consultation.  

1-800-647-4281

primeauforensics@gmail.com

An Accurate and Affordable Approach to Audio Enhancement

June 10th, 2014

oscilloscopeThe audio enhancement process is the number one forensic activity at Primeau Forensics. Audio enhancement, or sound enhancement, questions and assignments come into our offices daily from around the world. Audio enhancement helps people better understand words that were recorded but not clearly heard.

Last November I was asked by Jeff Morley to combine two versions of the Air Force One recordings from the day John F Kennedy was assassinated. Once my team and I had the recordings combined, the next step was to work on the enhancement process. 

As an audio forensic expert, audio enhancement is one of my favorite forensic activities. This is likely because when I started my career as an audio engineer, one of my first assignments was with the FBI. The experience was extremely rewarding because the two Detroit agents that came in to our recording studio, Ambience Recordings, were very appreciative and complimentary. I took an audio recording and used tools to reduce the unwanted background noise and enhanced the speaking portion of the recording. 

Audio enhancement is both an art and a science. It is an art because as forensic experts, we have tools like noise reduction, equalizers and compressors we use to create with similar to an artist who has paint, brushes and a canvas. We use these tools and artistically repair sound from sounding poor to enhanced and clear to better understand the speaking portion of the recording. 

Audio enhancement is a science because the tools have to be scientifically calculated and applied in specific orders depending on the experimentation with the order of application and the results from each application. I find myself using ‘control Z’ quite often during sound enhancement processes. 

Clients from around the world, including police departments and private individuals,  use digital pocket recorders to document and preserve a confession or other event in order to refer back to that event at a later date. The problem is that some of the time their recording does not go as planned. Background noise interferes more than planned because recorders pick up unwanted sound. Digital audio recorders do not record in the same manner that our ears perceive sound. When the digital pocket recorder is taken back to have the recording downloaded to a computer, the unwanted background sound is much more obvious then when the recording was created.

This is where our services as an audio forensic expert are sought out. After 30 years, we have become quite good and pretty quick at enhancing audio. Our speed and accuracy saves our clients money because many forensic experts take long periods of time applying various tools by trial and error. We, on the other hand, have the ability to recognize a noise situation and determine the order of processing necessary for audio restoration in a short period of time. 

In fact, we have started a service that accommodates our clients financially. Clients often have much higher than normal audio enhancement expectations. They hope the impossible can be made possible. Even the best forensic experts at Primeau Forensics cannot restore all sound to our client’s expectations.

This is why we have implemented a preliminary investigation process. This process allows us to send a sample of the restored recording to our clients to show them what is and is not possible. That way we can learn for a lesser rate if we can meet their expectations for audio enhancement. I am proud to say that in many cases we meet and even exceed their expectations. 

Techniques for Testifying Telephonically

May 9th, 2014

I recently testified telephonically for the United States Army. During my testimony I realized that there are several ingredients to a testimony by telephone. The following blog post will outline what I consider very important tips when testifying via telephone.

First, like all testimony, do your homework. Read all documents supplied repeatedly and nearly memorize them. Like testifying live, the lawyers, prosecutors and judges want to know what you are looking at while testifying. That is not to say looking at notes is bad, but instead to stress the importance of connecting your communication with the notes that are involved in the case. Remember, when on the phone, you are using only 20% of your communication tools. Body language and facial expressions are not being used during telephone testimony.

This segues nicely into the next tip; use voice tone and inflection to your advantage. For example, when we smile it lights up our face as well as our voice (if we are speaking). When testifying telephonically keep in mind the smile factor. Pay close emphasis to your voice tone and inflection when you are speaking since the majority of your other communication tools are not present. When making a strong point, use pausing and voice inflection to help the court feel your message since they cannot see you delivering your message.

Third, like when providing a testimony in person, it is crucial to rehearse with your lawyer and client. By rehearsing I mean practice a direct line of questioning as well as anticipate cross examination questions. Some of the lawyers I have worked with in the past insist on skipping this very important step. At Primeau Forensics, we take every step to make sure we are available for both our clients and lawyers during our time working together. Before the testimony we take extra care to organize, practice and rehearse; that way when it comes time to testify, there will be little to no mistakes, stutters or hesitations.

Remember, when testifying telephonically, the first rule is to always tell the truth. Keep in mind the words you are saying and the way you are saying them. Remember, the judge and jury are listening and evaluating you by your words because they cannot see your face or body language.

Malaysia Flight 370 Air Traffic Communication is Edited Latest News

May 1st, 2014

Listen to the Edited Audio HERE:

Audio clip: Adobe Flash Player (version 9 or above) is required to play this audio clip. Download the latest version here. You also need to have JavaScript enabled in your browser.

The Malaysian government finally released a recording today with their report of the conversation between Malaysian Flight 370 and Air Traffic Control. I had the opportunity to listen to the recording and have several concerns from an audio forensic perspective:

First, the very beginning of the recording is of high quality and the background ambiance and noise floor are very low. This is the quality we should expect with the technology that is available today. Then, at approximately 00:01:14 in the recording, the tone changes. At first listen it sounds as if a digital recorder is being held up to a speaker to create this portion of the recording. An edit occurs at this time, transitioning the higher quality to the lower quality recording. In addition, the background noise floor increases, while the tonality and quality of the voice communication decreases. I believe that the portion of the recording from 00:02:06 to 00:02:15 was created with a digital hand held recorder because noise in the room where the recording takes place can be heard, such as a drawer closing and papers being shuffled. There are also long gaps or silence in the communication where the room ambiance and background noise continue to be heard. Then at approximately 00:06:17 the conversation is clipped by an edit. Shortly thereafter the quality of the recording goes back to the same high quality as in the very beginning.

As an audio forensic expert I feel that with the technology and tools available today; why wouldn’t the Malaysian government have released a high quality version of this entire recording?

Also, why would they only release parts of the recording and not the complete recording? Surely the conversation must have been longer than seven minutes before Flight 370 went missing.

(800) 647-4281

 

Audio Enhancement – A Forensic Approach

April 25th, 2014

audio enhancementThere are two ways to look at audio enhancement, from a recreation standpoint and a business/legal standpoint. Most people searching for audio enhancement are looking for a solution to better hear a poorly recorded audio conversation. The audio recording may or may not be a very important piece of audio evidence.

The term “audio enhancement” can be used for a couple of different situations. First, with regard to ‘enhancing’ the quality of the listening experience – let’s call this ‘passive’ audio enhancement, since the goal is simply to enjoy a recording in the best possible environment. I am an audiophile; I love great sound when I listen to music. In that regard, audio enhancement is the activity of choosing the right equipment, careful placement of the speakers, careful placement of the furniture and taking your time gently balancing the equalization and stereo imaging.

Audio enhancement also helps a sound projection situation in sounding the best it possibly can. These situations can include a church service, professional speaker seminar, live concert, symphony or even a drive in theater. Yes, I believe drive in theaters will make a comeback.

In this situation, audio enhancement involves choosing the right speakers, then identifying the perfect placement for them with regard to sound source and audio ratio to audience. Live sound audio enhancement also involves activity as outlined in the previous example, like balancing the equalization and stereo imagery.

Audio enhancement for forensic applications, also known as forensic audio enhancement, also has similar activity as outlined in the previous samples – we’ll call this ‘active’ audio enhancement, since we are actively manipulating the quality of the recording itself in order to clarify what is being said. This activity requires a much more sanitary environment. An audio forensic lab is acoustically tuned and well stocked with the finest hardware and mind boggling software. This software is used in a specific order that is defined by each individual enhancement situation or court case.  With regard to audio enhancement for forensic applications, it is the skill of the audio forensic expert that makes or breaks audio enhancement success.

After 30 years of enhancing audio forensically, we are often asked by clients why our success rate is so high. I tell them that we began their enhancement process by analyzing the various reasons why their audio recording was so poor. Was it because background noise was louder than the desired conversation? In this case our goal is to clarify a recorded conversation. The audio forensic expert then determines whether to remove background noise first or boost the overall volume. With some cases the audio expert may apply other filters first like equalization, compression or re-sampling in order to better hear the words spoken.

There are free software programs available that do a pretty good job enhancing recorded conversations. Primeau Forensics recommends an audio software program called ‘Audacity.’  Audacity has equalization, format conversion and some similar processes and filters that other professional software programs have that we use at Primeau Forensics, like Adobe Audition. This is one approach if funds are low.

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.

We have experienced situations where the playback systems in court, as well as the reverberant acoustics, make it difficult to hear the enhanced audio recording. When the enhanced audio recorded evidence is accompanied with a certified forensic transcript, the judge and jury can read along with the transcript. It allows the court to better hear the enhanced recording.

Audio Enhancement – A Do It Yourself Forensic Approach

April 15th, 2014

audio_enhancementThere is an easy to follow ten step approach to audio enhancement that can be accomplished with free software (also known as freeware). Like many people I am the first in line to save money. I would like to begin by sharing two free software programs that anyone with audio enhancement needs can download. The first free software download I recommend for audio enhancement and audio editing is WaveSurfer. The second is a Soundforge product called Audacity.

Please note that I have chosen the links for free downloads from CNet.com, my favorite and most trusted site for downloading software with no spam or computer violations.

Download WaveSurfer or Audacity and open your digital audio recording to be enhanced and analyzed. At first glance these digital audio enhancement software programs will be overwhelming. Begin your exploration by importing the audio recording (file) you wish to enhance. In WaveSurfer, choose ‘file’ and then ‘open.’ In Audacity, use file import or file open. In this post we will not get into the differences between these two options; that will be for a later blog post. Subscribe to this blog and I will keep you updated with future information.

In the transform menu of WaveSurfer, you have options of the type of audio processing you would like to accomplish to better hear your audio recording. Three applications worth discussing here are ‘Amplify’, ‘Normalize’ and ‘Remove DC’. Feel free to check out the other application but remember, always save your original file in a safe location. Change the title of your work test using another file name. That way you will not override or erase the original ‘unfiltered’ version of your digital audio recording.

In the ‘Effect’ menu of Audacity, once your audio recording has been imported, look through your menu options. It is the ‘Transform’ menu that has a lot of audio filtering tools which are used for audio enhancement. Amplify, noise reduction, equalize and compressor are a few filters to begin studying as you learn the art and science of audio enhancement.

I recommend spending small amounts of time working on enhancing your audio recording so you avoid frustration. Since you saved your original recording, you can always go back and start over if you do not like the results of your enhancement processes. Remember, the ‘control Z’ application in Windows is great for going back one step when you do not like the results.

When you spend small amounts of time learning what each application’s purpose is, you should use your eyes and ears when deciding if your filter application was a success. Part of this learning process is developing your eye and ear coordination. Learning audio enhancement does not happen overnight so keep your expectations realistic. If you can raise the volume on a poorly recorded audio, then consider that an accomplishment; if you can reduce some of the background noise after the volume is increased consider that an accomplishment too!

In Audacity, the order of applying your filtering can make the difference in a better enhancement. Try raising your volume first. This is also called ‘raising the gain.’ Remember, when raising the gain you are raising the words spoken as well as the background noise. Be moderate when applying your audio filtering until you get the hang of it.

Next, try the noise reduction filter in Audacity. Be careful not to remove too much of the background noise because frequencies from the spoken word portion of your recording will be reduced during the noise reduction process.
Equalization could be a whole blog post by itself. In the equalization filter, with your audio recording open, apply some equalization by raising and lowering each vertical slider as you pay careful attention to the sound change that occurred. For now, get use to the various options in the equalizer filtering. One point worth making is you can improve sound by removing some of the equalization frequencies as well as adding equalization frequencies.

If you get to a point where the audio enhancement process is too frustrating or you have a question for one of our audio forensic experts, give our office a call at 800-647-4281. We will be glad to help.

Generation Loss in Analogue and Digital Recordings and Audio Forensics

January 2nd, 2014

It has become very easy to download and share music with friends. As an audio forensic expert, I am often asked why music loses quality when transferred from one person to another. In the following post I will share some explanations about generation loss, file format conversion and the relevance to audio forensics enhancement and authentication.

Back when I used to make 8-track and cassette copies of my record albums to listen to in my car or share with friends, the 8-track and cassette copies were considered first generation copies and sounded pretty good. When a copy was made from the first generation copy to create a second generation copy, it did not sound as good. This is because of ‘generation loss’. Although this is true for analogue recordings, it also is true for digital recordings.

Format conversion is a contributing factor to generation loss in 8-track to cassette analogue copies as well as CD to CD transferring. When a digital copy of a compact disc is created, the operator must pay careful attention to the copying process. It is very easy to change the format of the digital audio file without knowledge which will cause generation loss.

If the original CD which is a .WAV file is copied using any number of CD to CD copy software programs, it is very easy to change the format on the copy without noticing. Most people are pleased when they are successful that the copy plays rather than checking to make sure all the original characteristic in the original recordings are consistent in the copy.

For example, when copying a CD it is very easy to convert a .WAV file to an MP3 without knowing. Since most CD players and computers today will accommodate both file formats (.WAV and MP3), the average person can easily overlook this format conversion losing quality and causing generation loss.

MP3 is a lossy format which means that during the copying process some of the data is lost in an attempt to ‘compress’ the file making it smaller for internet use and storage reasons. This loss of data reduces the quality of the original audio recording.

From a forensic perspective, when a file is converted from.WAV to MP3, the meta data is stripped and altered making it very difficult for the audio forensic expert to authenticate the recording for litigation.

If you have an audio recording that requires expert authentication, make sure to send the original recording as it was presented to the expert and make and keep a copy for yourself. If you do not properly make the copy, worst case you will experience some generation loss and meta data alteration. The expert who is experienced in forensic investigation will have the best version of the recording to enhance and authenticate.

download-cv



Our demo video is coming soon!