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Archive for the ‘Forensic Audio Enhancement’ Category

Forensic Audio Enhancement -Equalization

Wednesday, July 1st, 2015

Forensic Audio Enhancement -EqualizationForensic audio enhancement is a scientific process. Remove the unwanted sound and increase the wanted sound. In many cases, based on our 34 years of experience, the wanted sound is most always dialogue.

The Use of Equalizers for Forensic Audio Enhancement

An equalizer is one of the most important filters or tools for audio enhancement. This is true for an audio engineer as well as an Audio Forensic Expert. There are many different types of equalizers with different capabilities. The core functions are always the same. Users may increase or decrease sound levels and frequencies. Frequencies that should be considered when performing forensic enhancement are 20 Hz to 20 kHz. All frequencies that fall into that range  are called ‘frequency bands.’ Each frequency band is typically marked by its center frequency, while the width of the band will vary between different equalizers. Some equalizers even allow the frequency band and the width to be adjusted.

These tools are crucial when performing a forensic audio enhancement. Noise and other unwanted extraneous frequency content is usually the biggest issue with audio recordings. Equalizers and filters offer the ability to remove narrow ranges of unwanted frequencies so that these unwanted noises can, for the most part, be removed from the recording. This focused process leaves all wanted frequencies like dialogue untouched.

Adobe Audition

One of the software programs we use at Primeau Forensics is Adobe Audition. It comes with the Adobe Creative Cloud Suite. Our favorite filter in Audition is the Multi-band Compressor. A compressor is another type of filter that helps enhance an audio recording to expose wanted sounds and remove unwanted sound. Another company, iZotope, has added some of their filters to Adobe Audition. Their noise reduction filter is also an excellent tool for removing unwanted sound.

Critical Listening Skills

Critical listening skills develop over time and are also referred to as ear training. Each of us has a different perception of sound. In other words, our hearing is unique to each individual. What we hear from a set of speakers or headphones is unique to us as individuals. In order to develop your critical listening muscle, you must experiment and observe. Remember, science is observation.

When using an equalizer, it’s important to be careful to boost or increase frequencies and amplitude (volume) gradually. It is also important to reduce or cut different frequency ranges selectively. This is because some of the time, removing a certain noise that appears to be at a certain frequency may seem to help. However, there could also be a lot of important wanted or voice content in that same frequency range. Making the proper adjustments with an equalizer requires both experience with the equipment, critical listening skills, and a lot of trial and error.

When we process an audio recording for forensic enhancement, we note the types of filtering and associated outcomes in our work notes. Work notes include the various filters applied to a recording, the differences in sound quality and intelligibility. The settings are then noted. Experience, the more time spent and the more audio enhancements that are successfully completed. We are extremely familiar with frequency ranges and improving the quality of audio recordings.

Now listen in with Audio and Video Forensic Expert Ed Primeau as he discusses the use of equalizers in forensic audio enhancements.

Audio Enhancement – Noise Reduction

Friday, April 3rd, 2015

Audio Enhancement - Noise ReductionMost recordings that I come across as an Audio Forensic Expert require audio enhancement. This is because they are made in poor conditions and have an abundance of noise. Though there are many ways to reduce the noise floor in a recording, there is no guaranteed method. The noise floor can be defined as a sum of all of the unwanted signals in a sound source. This will include any background noise in an environment such as cars driving by, televisions or radios, or even other people besides the desired person speaking.

When reducing the noise is the best option, there are two common ways to do so in most audio editing software: noise reduction processing and filtering or equalization. Both processes have benefits and side effects when used to remove noise from a recording.

The most important thing to remember when removing noise from a recording is that the goal is to enhance or clarify the desired signal. Every audio recording is different, and as an Audio Forensic Expert it is my job to analyze and process each recording as needed. It takes training and experience to recognize what a recording needs in order to enhance or clarify it effectively.

Now listen in with Audio and Video Forensic Expert Ed Primeau as he discusses the use of noise reduction in forensic audio enhancements.

photo credit: Neve Compressors via photopin (license)

15: A Step-by-Step Approach to Forensic Audio Enhancement

Monday, January 19th, 2015

15: A Step-by-Step Approach to Forensic Audio EnhancementOne of the most common jobs for an Audio Forensic Expert is enhancing a digital audio recording for intelligibility and clarification.  Audio evidence is often recorded in less than optimal situations with poor quality equipment. This evidence can be vital to a case and when the content of the recording cannot be heard, the evidence can become useless.  This is why the audio enhancement process is one of the most important jobs as an Audio Forensic Expert.

There is no one way to enhance an audio recording because every recording is different and will have its own issues that make the enhancement process necessary. At the same time, it is important for the Forensic Expert to be aware of the processes available so they are prepared to handle any enhancement case that comes their way.

Critical Listening

To begin the enhancement process, the Forensic Expert should use critical listening.  Before adding any processing to the audio, they should listen through the recording multiple times and make notes on the issues they hear with the recording.  Noting different sections of the audio and marking these points can be extremely helpful when fixing different problems in the recording.

Diagnostic Tools

Some audio software includes processors that help fix clipping or clicking issues in the recording.  Using this process first will help clean up the audio as much as possible before delving into more advanced techniques.  Noise reduction is also a very helpful process for removing any background noise such that is consistent throughout the recording.

Dynamics Processing

Many recordings I receive have an overall low level to begin with and simply need an increase in gain. Compressors as well as gain plugins can help raise the overall level of the recording. Compression will also help balance all of the signals in the recording.

Equalization

Equalization is another extremely helpful tool for audio enhancement.  This will allow the Forensic Expert to remove unwanted frequencies and frequency ranges by varying amounts, as well as boost desired frequencies. When using an equalizer, the Forensic Expert should experiment using their knowledge of frequencies and what they see in the recording.

Now listen in with Audio and Video Forensic Expert Ed Primeau as he discusses the structured approach to forensic audio enhancements.

 

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I received credentials from two technicians, then a third person ended up doing all the work and kept in touch with me by e-mail. I never saw any proof that the work was done and they told me they found nothing. They could not tell me what was making the noise or the lights. A waste of $750.00.read more
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Excellent work. Primeau took a low light camera recording of vandalism at my home and converted the video to images that we used to identity the vandals. Additionally, Primeau was able to identify characteristics of the vandals car that were used for a positive identification. Services were efficient, timely, and professionalread more
Todd Conte
15:18 27 Aug 18
Ed and his team are great! I took in footage of my boyfriends dog being stolen and they were so willing to take every step possible to enhance the video to retrieve the information we needed. The resolution on our camera/video wasn't great (our fault, not theirs) and they were unable to get the information we needed BUT they guided me in the next steps to take. Thank you guys!!read more
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