The 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.
The 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.
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.
There 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.
There 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.
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.
Back at the end of October, I was contacted by Nicole Bogart from the Global News in Toronto who asked that I conduct a voice identification between known samples of Mayor Rob Ford and a male caller to a radio show named Ian. They believed that the caller who was defending the mayor was not a person named Ian but rather Rob Ford himself.
In the video below, I explain my process and play samples of the audio’s that were used to compare and arrive at my conclusion.
To read the full Globe story, click HERE: http://globalnews.ca/news/950387/forensic-audio-experts-mixed-on-whether-ian-from-etobicoke-caller-was-rob-ford/
At the end of this blog post is a fully restored digital audio file available for listening and downloading of the government conversation that occurred at the time of the assassination of President John F. Kennedy. The Announcer at the beginning of the recording is the poorest quality of the entire 2:01:59.
This is a combination merged from two copies that were in existence. The first copy was released by the government and referred to as the ‘LBJ tapes’ in the early 1970’s. Another longer copy surfaced in a Philadelphia private auction in 2011. This longer copy was found in the belongings of the late General Clifton. Thanks to Bill Kelly, a veteran JFK researcher, Primeau Forensics has combined the contents of both recordings and fully restored them.
In this enhanced recording, you will hear conversations from Air Force One over the Pacific Ocean as they abort a trip to Japan and turn around, mid-air, to return to the mainland after learning about the assassination of the President of the United States. These recorded conversations between Ground Command, the White House and Air Force One include code names such as ‘Duplex,’ ‘Digest,’ ‘Volunteer,’ ‘Liberty,’ ‘Witness,’ ‘Crown,’ ‘Baker,’ ‘Watchman,’ and ‘Tiger.’
During the call they make arrangements to transport John F. Kennedy’s body, his widow, President Johnson and the other 40 people safely back to Washington DC. The carefully coordinated and strategically executed planning is heard in this recording. Decisions about media coordination on the ground at the White House, the post-mortem autopsy to be performed by law and President Johnson’s conversation with JFK’s mother, Rose Kennedy can also be heard.
It may take a while to get your ears acclimated to this early, mobile technology. Primeau Forensics has carefully removed unnecessary radio static and squeals to accommodate better listening. It is recommended that you use a combination of speakers and headphones to best listen to these recordings.