The Art and Science of Removing and Restoring Audio From Video

5570870656_81ed95b87c_oAs an audio forensic expert I often receive video evidence that has an audio track that is difficult to understand. Even though the video presents clues and truth about the events as they occurred in the video the audio track also provides an opportunity of clues and events as they occurred to help process the litigation. As both an audio and video forensic expert I am often asked to clarify or enhance the audio from a video. The process of removing the audio track for enhancement and clarification is crucial to the success of presenting the enhanced or clarified audio evidence in court.

First of all, most people look for audio enhancement when they come to me as an audio forensic expert, and I often start our conversation out by explaining to them it’s better to use the word ‘clarify’, because judges and courts don’t understand the semantics and the difference between the words ‘enhanced’ and ‘clarified’. Clarified has less harmful meaning than enhanced. If I’m in court and I tell a judge that I’ve enhanced this audio one of the first things the judge thinks is that something has been done to it to take it or change it from its original state, and that’s not the case. But, most people are educated and search for audio enhancement when they’re looking for an expert to help solve their problem or clarify their evidence.

Removing the audio track to be processed requires the video forensic process of loading the evidence into a software program like Premiere Pro or Final Cut Pro then exporting the audio track in full quality from that video to create a sub-file, which is an audio only file. That file is then imported into Adobe Audition or Sound Forge depending on the nature of the clarification that is necessary. I find Adobe Audition to have more powerful tools to help the clarification process. I use tools in Audition in order to remove unwanted noise and increase the wanted sounds which could be speech, gun noises and other extraneous noises to the environment which could be crucial to the understanding of the events as they occurred. The tools that I use, that I apply to the audio export file, are used in accordance with accepted standards in the scientific community so that if this case were to go court I could explain, by my work product and my notes, what filters or tools were applied to this digital audio file in order to clarify the sounds to be better heard, or the speech to be better understood. Once I’m satisfied with the clarification process and I believe the file has been enhanced as much as possible the exact file, in it’s restored process – which is more clarified and enhanced – is re-imported to the video software program and reconnected to the original video evidence. At that point it is synched with the audio file that was originally part of that video evidence and exported to create the clarified version of that evidence. If there’s any video work that needs to be a part of that process, such as sharpening of the image, zooming in of the video image, that is also done before exporting the new clarified evidence to be used in the litigation. The processes are accepted in the scientific community and an important part of the forensic expert’s job. Keeping track of the steps along the way – including chain of custody of the evidence – is crucial and part of the audio forensic clarification/restoration process.

photo credit: J·K·L (87/365) via photopin (license)



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