One 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.
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.
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 it is consistent throughout the recording.
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 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.