Most 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; 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.