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Digital Audio Forensics Fundamentals
Cover
Half Title
Series Information
Title Page
Copyright Page
Contents
Acknowledgements
Abbreviations
Chapter 1 Introduction
Scope
Foundations
Sub-disciplines overview
Research
Capture
Authentication
Enhancement
Acoustic analysis
Voice analysis
Summary
References
Chapter 2 The history of audio forensics
Technological developments
The analogue years
The digital years
Audio forensics’ beginnings
Notable cases
Summary
References
Chapter 3 Forensic principles
Introduction
End users
Admissibility
Best practices
Standard operating procedures
Bias mitigation
Confirmation bias
Base-rate fallacy
Prosecutor’s fallacy
Texas sharpshooter’s fallacy
Optimism bias
Contextual bias
Allegiance bias/adversarial allegiance
Peer review
The forensic laboratory set-up
Environment
Equipment
Workstation
Software
Audio equipment
Other devices
Other equipment
Library
Documentation
Summary
References
Chapter 4 The human auditory system
Introduction
Overview of the human auditory system
Magnitude perception
Threshold of audibility
Frequency perception
Equal loudness contours
Critical bands
Masking
Simultaneous masking
Binaural masking
Informational masking
Non-simultaneous masking
Spatial perception
Auditory fatigue
Summary
References
Chapter 5 Key audio principles
Introduction
Forensic audio versus studio audio
Capture environment
Studio audio
Forensic audio
Equipment
Studio audio
Forensic audio
Microphones
Studio audio
Forensic audio
Operators
Studio audio
Forensic audio
Specifications
Studio audio
Forensic audio
Devices
Studio audio
Forensic audio
End user
Studio audio
Forensic audio
Capture
Sample frequency
Quantisation
Channel configuration
Bit rate calculation
Interpolation
Extrapolation
Analysis methods
Time domain
Power
Decibels
Amplitude
Normalisation
Frequency domain
Fast Fourier Transform
Input samples
DFT points/FFT length
Zero padding
Power spectral density (PSD)
LTAS
Ordered
Summary
References
Chapter 6 Audio encoding
Introduction
Filename
Filename extension
File structure
Container
Audio data
Uncompressed audio
PCM
Delta modulation
ADPCM
WAVE
AIFF
Compressed audio
Perceptual encoding
MP3
Bit rate
Sample rate
Channel modes
Construction
ID3 tag
Encoding process
Quantisation and scaling
Huffman encoding
Side information
Bit-stream formatting CRC word generation
MPEG-2 (AAC)
MPEG-4 (AAC)
Windows Media Audio (WMA)
Vorbis
AC-3
DSS
AMR
Perceptual encoding artefacts
Bandwidth reduction
Pre-echoes
Double-speak
Birdies
Speech reverberation
Loss of stereo image
Phase shift
Holes and clusters
Summary
References
Chapter 7 Preparatory analysis
Introduction
Exhibit imaging
Physical
Digital
Instruction
Summary
References
Chapter 8 Audio acoustics
Introduction
Overview of sub-disciplines
Timing information
Number of acoustic events
Identification of type of sound
Identification of the source of the sound
Location of the sound source
The acoustics of a gunshot
Muzzle blast
Shockwave
Reflections
Analysis methods
Pre-processing
Critical listening
Waveform analysis
Envelope analysis
FFT analysis
Cross-correlation
Summary
References
Chapter 9 Speech forensics
Introduction
History
Variables
Analysis methods
Auditory
Acoustic phonetic approach
Spectrographic
Automatic
Reporting methods
Binary decision
Classical probability scale
Likelihood ratios
UK position statement
Summary
References
Chapter 10 Audio enhancement
Introduction
Quality versus intelligibility
Measurement methods
Preparatory analysis
Background noise
Clicks
Transient noise
Continuous tones
Competing speakers
Broadband noise
Reverberation
Speaker levels
Distortion
Overall signal magnitude
Documentation
Enhancement suitability
Manipulation versus enhancement
Quality issues and solutions
Clipping
Cause
Effect
Solution
Clicks
Cause
Effect
Solution
Ambient noise
Cause
Effect
Solution
Broadband noise
Cause
Effects
Solution
Background music
Causes
Effects
Solution
Hum
Cause
Effect
Solution
Reverberation
Cause
Effect
Solution
Amplitude
Cause
Effect
Solution
Order of operations
Step 1: Fix distortions
Step 2: Stereo source separation
Step 3: Remove static redundant data
Step 4: Gain correction stage one
Step 5: Remove dynamic redundant data
Step 6: Remove noise
Step 7: De-reverberation
Step 8: Gain correction stage two
Step 9: Normalisation
Step 10: Time-stretching
Step 11: File output
Step 12: A/B comparison
Step 13: Peer review
Enhancement reporting
Exhibit quality
Enhancement process
Generated exhibits
Transcriptions
Summary
References
Chapter 11 Audio authentication
Introduction
Study of manipulations
Trimming/cropping
Deletion
Splicing
Speech synthesis
Preparation
Initial assessment
Proprietary recordings and video
Exemplar recordings
Cases where a recording is purported to be from a specific recorder
A case where there is no information in relation to the recording device
Database
Analysis
Critical listening
Preliminary overview
Record events
Background sounds
Foreground information
Critical listening documentation
Considerations for video
Critical listening breaks
Filename
Theory
Application
Filename extension
Theory
Application
File location
Theory
Application
File structure
Theory
Application
File metadata
Theory
Application
File specifications
Theory
Application
Amplitude statistics
Theory
Application
ENF criterion
Theory
Application
MDCT coefficients
Theory
Application
Butt splice detection
Theory
Application
Spectrogram
Theory
Application
Power spectral density
Theory
Application
Long-term average spectrum (LTAS)
Theory
Application
Long-term average sorted spectrum
Theory
Application
Compression level analysis
Theory
Application
DC bias
Theory
Application
Zero padding
Theory
Application
Phase
Theory
Application
Quantisation level
Theory
Application
Codec analysis
Theory
Application
Analysis of Results Summary
Drawing conclusions
Conclusion reporting
Summary
References
Chapter 12 Forensic reporting
Introduction
Purpose
Structure
Cover page
Contents
Introduction
Examiner summary
Summary of those involved
Information regarding instruction
Points of instruction
Purpose of the report
Conflicts of interest
Scope
Facts
Assumptions
Limitations
Preparatory analysis
Methodology
Statement of methodology
Results
Analysis and results
Discussion
Opinion
Statement
Appendix
Glossary
Tools
Conclusion reporting scale
Exhibits reviewed
Exhibits generated
Bibliography
Examiner qualifications and experience
Summary
References
Chapter 13 Research
Introduction
The scientific method
Observation
Literature review
Hypothesis
Experiment
Results
Discussion
Reporting
Summary
References
Glossary
Index
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