Advances in Audio Restoration

Advances in Audio Restoration

Don Maue, Joseph C. Kush
Copyright: © 2015 |Pages: 16
DOI: 10.4018/978-1-4666-5888-2.ch598
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The need for audio forensics is deeply related to the need to find the meaning in sound. Without meaning, there is no need for audio forensics. Audio restoration has been defined as a post-production task that edits and processes audio (Godsill & Rayner, 1998). The purpose of the editing and processing can vary. Audio restoration, or ‘cleaning up the audio’ is performed in countless ways using a variety of tools (Godsill, Rayner, & Cappe, 1996).

Audio forensics does not imply the preparation of sound for legal proceedings. While that may be one of the many purposes of audio forensics, the term is actually much broader and more inclusive. Audio forensics have been used in a number of high profile, public examples including the Watergate tapes, the Zapruder recording of the Kennedy assassination, homeland security (Owen, 2003), terrorism (Dickey, 2007), and in listening to black box recordings associated with airline malfunctions. However audio engineers and even non-professionals are increasingly using the technology in many endeavors including for example, the remastering of audio recordings, creating podcasts and even cleaning up the sound of a personal, home movie (Farid, 2009). These advances have occurred so rapidly that the field of forensic comparison sciences is currently undergoing a paradigm shift (Morrison, 2009) much like is occurring with DNA comparisons. In an attempt to standardize these listening experiences the International Telecommunications Union created a standard for audio quality assessment: PEAQ. Additionally, a 12 Step Methodology for Audiotape Authenticity (Owen, 2003) and Methodology Procedures for Audio Authenticity, are available through the Audio Engineering Society; an outline of steps to identify edits, alterations, and duplication in the audio portion of recordings. Relatedly, the Scientific Working Group on Digital Evidence (2012) is creating standards for the forensic examination of audio recordings that may serve to improve standards across the whole field of forensic audio examination.

Key Terms in this Chapter

Denoise: Denoise utilizes a two-step process to remove noise from an audio program.

Decibel: A unit of measurement for relationships of voltage levels, intensity, or power.

Click Removal: The term refers to localized bursts of impulsive noise present in an audio signal.

Dither: The introduction of a small amount of analog noise, prior to the analog to digital conversion, designed to smooth out square waves associated with low level signals.

24-Bit Audio: 24 bit audio files will contain more resolution and range of dynamics compared to the other files (e.g., 8 or 16 bit).

Digital Audio Workstation: DAW software aggregates multiple disparate recordings and blends them into a consumable format.

Audio Restoration: A generalized term for the process of removing imperfections (such as hiss, crackle, noise, and buzz) from sound recordings.

Audio Forensics: Audio Forensics is a new science that utilizes technology to separate important semantic content from unwanted sounds in a digital audio file.

Dynamic Range: The maximum dynamic range of a recording is the number of bits multiplied times 6.11.

Word Length: Word Length is also known as bit depth, determines the dynamic range of a digital audio file. Word Length also influences the fidelity of audio when processed.

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