Forensic Audio Enhancement, Voice Enhancement

What is Forensic Audio Enhancement?

Forensic audio enhancement is the scientific process of clarifying audio recordings using non destructive techniques to preserve speech intelligibility so that the trier of fact can make determinations about the events within the recording. Above all, the goal of forensic audio enhancement is to better hear dialogue by removing unwanted noise. This scientific process is also known as speech enhancement and voice enhancement.

Forensic Audio Enhancement Process

We apply enhancement techniques to remove sounds like static, furnace and air conditioning fans, hums and other distracting sounds. For this reason, these distracting noises are also known as “unwanted sounds”.

Then, once we remove the  unwanted sounds, we can apply audio enhancement processes. These enhancement processes will increase the “wanted sound” like speech. In Fact, the enhancement processes will increase voice quality and dialogue intelligibility through signal processing. Our forensic audio experts apply enhancement services using state of the art equipment to increase the intelligibility of your audio recordings used as evidence in court. 

In addition, the same is true for for the audio quality of a video clip. We also perform forensic audio enhancement on video recordings like police dash cameras, body cameras, Ring CCTV devices to improve speech. That is why we have additional information for your review here how to enhance audio in a video file. 

Types of Recordings for Audio Enhancement

So you better understand, we perform audio enhancement on a variety of audio recordings. These including but not limited to:

  • Recordings made on smart phones
  • Deposition video
  • Digital handheld recorder
  • Digital pocket recorder
  • Cassette tape
  • Micro & mini cassette tape
  • Law enforcement dash cam
  • 911 dispatch
  • Courtroom recording
  • Confidential informant
  • Wire tap
  • Voice mails

Forensic Audio Enhancement Methodology

Critical Listening

file 300x225 - Forensic Audio Enhancement, Voice EnhancementFirst, we listen to the recording critically. Critical listening is a skill that is developed over time through training of the ears. It is key for identifying sections of the recording that require audio enhancement.

The critical listening criteria are characteristics in the audio recording which include recording levels, frequency ranges, or signal to noise ratios. We perform critical listening with both professional grade monitors (speakers) as well as noise cancelling headphones to ensure the most accurate listening experience.

Equalization (EQ)

sound board 1416985 200x300 - Forensic Audio Enhancement, Voice EnhancementAfter that, Equalization can be applied.  Equalization is a filtering process that can reduce unwanted frequencies or increase wanted frequencies. The EQ process will filter distracting noises first to ensure the highest success of the enhancement.

The EQ process is most commonly done first to ensure that these irrelevant frequencies to not interfere with other processes.  Specifically, equalizers are used to filter out hums, buzzes, a/c compressor noise or other unwanted tones that are banded noise.

Noise Reduction & De-Reverb

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Third, we must remove all types of interference’s or noises. Noise Reduction improves the signal to noise ratio by reducing distracting sounds from a recording. These distracting sounds hinder the speech recognition ability of the listener. Noise removal is the most effective processing technique for voice enhancement.

The noise reduction process uses a noise profile to systematically reduce unwanted frequencies without affecting the dialogue or human voice signals. We also have tools that reduce reverberation or echo cancellation.

Compression/Gain Adjustment

Fourth we need to improve the dynamic range of an audio recording. Compression raises, lowers and balances the volume levels of a given section. Gates and further compression can also help remove unwanted sound or boost desired sound. If there is excessive background noise, a gate can be helpful before most of the other processors, especially compression.

Forensic Transcription

Finally, the forensic transcript may become essential for verification of dialogue spoken or events that occur in the recording.  The forensic transcript combined with the speech enhancement or voice enhancement makes an exhibit more relevant to an investigation.

Enhanced Audio Courtroom Use

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Often times when a lay person processes an audio recording, these changes can effect in a negative effect. The authenticity of the events change, and inaccurate representation of the events makes the recording inadmissible in court. This is often times based on an inaccurate perceptual quality change.

A qualified forensic expert must follow the best practices established by the scientific community. This includes performing the audio enhancement services accurately, documenting the procedures used and presenting the findings to the Trier of Fact. In conclusion, in order to identify dialogue with accuracy, a successful audio enhance or speech enhancement investigation is essential.

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