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Module XXII – Audio File Forensics

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News: UCD to Lead Way in
Audio, Video Forensics
Source: http://www.rockymountainnews.com/
By Bill Scanlon,
February 5, 2008 at 4:45 p.m.
Denver may become a mecca for police nationwide who need to solve crimes by carefully analyzing audio and video
evidence.
A professor at the University of Colorado at Denver has won $710,000 in Federal Earmark Grants to establish a new
National Center for Audio/Video Forensics.
Housed in UCD's Department of Music and Entertainment Industry Studies, the center would establish a "cutting-edge
forensics center" to spur new knowledge and methods in the field of audio and video forensics, Professor Richard Sanders
said.
Undergraduates, graduates and professionals could learn the latest techniques in, say, tracking phone use by prisoners, or
discovering when someone is impersonating another's voice to move cash out of a bank account.
Voice biometrics would work in combination with fingerprints, DNA and facial recognition to identify suspects.
The grant will give real-world research opportunities to students in recording arts, statistics, computer science and the
health sciences programs, Sanders said.
It also will give local police, attorneys, investigators and homeland security officers access to state-of-the-art forensics
technology, he said.
Sanders' work in audio forensics was tapped by investigators working the JonBenet Ramsey case, the Kobe Bryant case, the
Columbine High School shootings and the Oklahoma City bombing trial.
The grants were awarded by the U.S. Department of Justice. Additional support came from the university, the international
Audio Engineering Society, the American College of Forensic Examiners, the American Board of Recorded Evidence and the
National Law Enforcement Technology Center.

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News: Audio Forensics Experts
Reveal (Some) Secrets
Source: http://www.wired.com/

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Module Objective
• Audio Forensics
• Why Audio Forensics?
• Fast Fourier Transform (FFT)
• Methodologies
• Audio Forensic Process
• Sound Recordings as Evidence in Court Proceedings
• Tools
This module will familiarize you with:

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Module Flow
Audio Forensics
Methodologies Fast Fourier Transform
Tools
Sound Recordings as
Evidence in Court Proceedings
Audio Forensic Process
Why Audio Forensics?

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Audio Forensics
Audio Forensics is the appellation for the engineering discipline involving the analysis,
evaluation, and presentation of acoustic evidence in a judicial inquiry normally leading
towards a presentation in court
The application of audio science and technology aids to investigate and establish facts in
criminal or civil courts of law

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Why Audio Forensics?
Audio Tape Verification and Authentication
Monitoring suspicious criminal targets
Audio Tape Enhancement
Voiceprint Analysis
Tracking missed information
Monitoring employees

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Use of Voice as a Tool
Investigators use audio for solving the case which needs listenability and
intelligibility of the audio
Scenario: Person X gave a call to police and informed about a
murder. Cops rushed to the place where the incident took place
but there they could not find any clue. The only thing they had was
a call recorded. Now the recorded voice is analyzed to resolve the
case.

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Fast Fourier Transform (FFT)
Fast fourier transform is an algorithm used to analyze the
authenticity of the audio
It breaks the audio signal into time-frequency spectrum
It checks for discontinuities in the audio spectrum
• Audio signal: The normal spectrum in time-frequency form
• FFT analysis graph: The graph that shows details of discontinuities in the
audio signal spectrum
It generates two graphs:

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FFT Analysis: Screenshot 1

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Discontinuities on A’s background
B’s Background

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Methodologies of Audio Forensics
Voice identification
Audibility analysis
Audio enhancement
Authenticity analysis
Sound identification
Event sequence analysis
Dialogue decoding
Remnant signal analysis

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Voice Identification
Voice identification is comparison of known suspicious voice to the recorded voice
It compares elements of voice such as bandwidth, fundamental frequency, resonance, pitch
striations, vowel formal trajectory, prosody, pattern of breath, and special speech style of the
speaker
Voice phonetics of each individual differs from the other
Phonetic components of the recorded voice are analyzed and compared with the suspect to
identify the voice
Digital or analog spectrograph is used for voice identification

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Voice Identification (cont’d)
• Check whether the recording consists of sufficient amount of
voice for analyzing
• Look at the quality of the voice
• Check if the conversation volume is high when compared to the
background noise
Pre-identification considerations:
Check

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Audibility Analysis
Audibility Analysis is the
reconstruction of an
acoustic event to determine
whether the event is
audible for a person of
average hearing ability
It checks whether the audio
signal is audible or
obscured by the noise or
masking signals
Make use of the
aural/spectrograph,
acoustical measurements,
and acoustical simulation
to analyze the audibility of
speech, siren, alarm, etc. at
a particular place or time

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Audio Enhancement
Audio enhancement is the technique of improving the quality of the audio in terms of
listenability and intelligibility
Listenability enhancement involves applying equalization, compression, amplitude
increment, and limiting techniques to make an audio signal intelligible
Intelligibility enhancement is breaking the audio in small sections, processing them
independently, and thus assembling them
• Spectrographic analysis
• Complex de-convolution filtering
• Wideband and multiband compression
• Amplitude increase and limiting
Intelligibility enhancement procedure involves:

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Audio Enhancement (cont’d)
• Clicks caused due to the discontinuity in recording
• Hiss caused due to the cassette tape
• Engine noise caused due to car cameras
• Background noise recorded while recording a call
• Hum, buzz, and pop noises caused due to power sources
• Ruffling sounds caused while recording the audio through hidden
recorders
The type of noises that are removed or minimized
through enhancement technique:
The sound that makes desired audio unintelligible is termed as noise

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Audio Enhancement: Screenshots

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Authenticity Analysis
Authenticity analysis determines whether the audio origin is same as
what the acoustic event is representing
• Aural analysis
• Magnetic tape development
• Physical inspection
• Frequency
• Manufactured date
• Amplitude and formant analysis
It involves suspicious recording to verify the
authenticity by means of:

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Sound Identification
Sound identification involves comparison of sound under investigation to a known sound
It is critical in determining whether a barely audible sound is a voice or an acoustic illusion
caused by the recording device or an extraneous sound source
Sound identification techniques generally require original recording device for comparison of
sound
Use spectrograph for the comparison of sound

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Event Sequence Analysis
Event sequence analysis is the analysis of the sequence of acoustic events in the
recording that determines components such as time, frequency, and amplitude
It verifies authenticity of the recording
It reveals absolute duplication of events

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Dialogue Decoding
Dialogue decoding is the extraction of the message from the recording
It is based upon voice patterns in a spectrograph

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Remnant Signal Analysis
Remnant signal analysis is analyzing the segment of audio that seems to be
irrelevant for investigation
The segment of audio/recording can be the disturbance caused due to the
surroundings, machine rhythms, reverberation, etc.

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Integrity Verification of the
Audio
Integrity verification of the audio is necessary to qualify
or disqualify the tape for further proceedings
Tape editing technology is editing the audio recording for
gaining audibility
Electronic tape editing can be noticed with acoustic
irregularities in the audio through devices that can detect
editing
Few alterations to digitized recording are difficult to be
traced, if they are copied on other tape

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Integrity Verification of the
Audio (cont’d)
• Total loss of the audio signal
• Change in the speaker’s frequency response during
different telephone conversations
• Spikes that provide audible sounds of short duration
(attributable to normal stop, start, and pause functions
of the recorder)
• Traditional tape technique involves suspecting the
modifications made by checking and noting:
• Unexplained transients
• Equipment sounds
• Extraneous voices
• Inconsistencies with provided written information
Suspicious acoustic events:

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Audio Forensics Process
Spectrographic analysis
Preparation of spectrograms
Conversion of analog audio to digital audio
Preliminary examination
Preparation of copies
Preparation of exemplars
Evidence handling

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Audio Forensics Process:
Evidence Handling
Gather all the tapes that are recorded and considered as
evidence
It is essential to identify, maintain physical integrity, and
to ensure the audio as evidence for forensic purpose
Critically listen to the original tape
Do physical inspection of the tape
Check if the tape is tampered
Document all the actions that are taken to protect the
evidence

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Preparation of Exemplars
It involves comparison of original spectrum to unknown voice
samples
Here, suspect’s voice is recorded, where dialogue in the original
recording is repeated
Exemplars are prepared by investigators
Check the performance of the recorder used for original recording
Conditions of recording and speech delivery must be duplicated for
easy analysis
Analyze the exemplar to compare voice in audio file with the voice of
the suspicious person
It offers voice identification

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Preparation of Copies
Preserve original recording for court proceedings
Create copies of recording so that the original tape is not
corrupted
For voice identification, look for direct copies of the recording
It enhances the original recording thus removing noise for better
audibility
Playback of evidential audio depends upon track determination,
azimuth alignment, speed accuracy, and reproducer of the
recording

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Preliminary Examination
Check the audio files that are to be examined
Determine the integrity and authenticity of the audio
Check whether the recording is original or modified
Determine if the known and unknown voice samples
meet guidelines to allow further examination
Analyze the quality of voice samples by suppressing
the noise or distortion

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Audio Forensics Process: Analog
to Digital Conversion
• Use A-to-D converters such as Successive approximation ADC, Flash ADC,
Dual Slope ADC, etc.
Convert analog audio to digital audio
• Use the tools such as Zune music recovery Software for
recovering/extracting the corrupted audio
Extract the audio, if it is digital and corrupted
• Avoid mismatch of the extension/format of the audio file
Check for compatibility of audio file

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Audio File Formats
http://www.fileinfo.net/

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Audio File Formats (cont’d)

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Preparation of Spectrograms
Use sound spectrograph for preparation of spectrograms
Investigator identifies the speech by formatting and marking the spectrogram
Retention of spectrogram is necessary until the completion of the investigation

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Spectrographic Analysis
It involves pattern and aural comparison of the voice
sample
Perform spectrum and waveform analysis of the audio
signals
Pattern comparison is the comparison of original and
enhanced sample, similar speech sound, and number of
comparable words depending upon the pitch and energy
distribution

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Sound Spectrograph
Spectrograph is the device used for visualizing the graph or spectrum of the audio
Spectrum enables the investigators to detect the addition or enhancement made to the audio
Disguised voice cannot direct the spectrograph in a wrong way
The spectrum of the audio signal is displayed in frequency and amplitude form
Time is on x-axis, with frequency on y-axis and voice energy in the form of gray scale
(spectrum)
Audio signal spectrum

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Sound Recordings As Evidence In Court
Proceedings
• Testimony by defense, plaintiff, or government witnesses of tampering or
other illegal acts
• Problem description should be complete which includes exact location of
recording, type of alteration, scientific test performed, etc.
• The original tape must be provided as duplicate tape cannot be authenticated
and are not accepted for examination
• Tape recorders and related components used to produce the recording must
be provided
• Written records of any damage or maintenance done to the recorders,
accessories, and other submitted equipment
Audio evidence in courts should be accompanied with:
Witness

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Audio File Manipulation
• Deletion
• Deleting the unwanted portion of the audio by splicing or using a recorder
• Obscuration
• Involving distortion to the recording thus leaving the audio unintelligible
• It is used for masking the audio
• Transformation
• Altering the portions of audio for changing the meaning of the conversation
• Synthesis
• Generation of additional text such as background sound or conversation to original
recording is termed as synthesis
Alterations or tampering in a recording can be through:
These can be suspected with gaps, fades, transients, and equipment sounds of
the altered recording

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Tools

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DCLive Forensics
• DSS filter
• It recovers speech from recordings that contain loud music or
other coherent noise
• Adaptive filter
• It is used in audio applications where the ambient noise
environment is constantly changing
• AFDF Forensics Filter
• It automatically adjusts itself to varying noise environments with
no noise sample being taken
It consists of:
DCLive Forensics tool analyzes, enhances, and improves difficult recordings using a
system with a sound card

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DCLive Forensics (cont’d)
• It allows the mathematicians, scientists, and engineers to create their own transfer
function using a polynomial expression
Polynomial Filter
• In forensic audio applications, it is used for removing in-band and out-of-band
extraneous noises
Spectral Filter
• It provides a method for displaying audio as a waveform in time, frequency, and
intensity form on the graph
Spectrogram
• It is used to repair signals, which were either clipped by digital or analog mechanisms
DeClipper

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• It is designed to be used in real time intelligence gathering and Forensics surveillance
situations
• It allows to go back and listen to something that you may have heard during real time
operation of the software
Flashback Recording
• It automatically logs an unedited raw version of the recording along with the enhanced
version with a backup
Dual Stream Recording
• It allows the recorder to start and stop itself based on the presence or lack of presence of
an audio input signal
VOX Record Activation

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• Each recording event will be marked with the exact time and date of the individual
recording
Auto Date and Time Stamp
• It automatically starts a new file every time the 2 gig limit is reached and never misses a
beat
Unlimited Recording Time
• These are FIR (Finite Impulse Response) filters that exhibit a high degree of out-of-
band attenuation
Brick Wall Filter

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Features of DCLive Forensics
Higher resolution spectral filter offering a 32,000
band EQ
Improved time domain adaptive filter
All popular formats of audio are supported
Tune library organizes the investigator’s collection
Impulse filter enhancements

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Zoom H2 Portable Digital Recorder
• It has built-in USB 2.0 interface
• It has On-board chromatic guitar/bass tuner
• Time stamp and track marker functions in Broadcast WAV
Format (BWF)
• It has 512MB SD memory card
• Accommodates up to 4GB SD memory cards
• Auto Gain Control (AGC) for pristine recordings
• Low-cut filter eliminates wind noise
Features:
Zoom H2 portable digital recorder provides brilliant stereo recording in an ultra-
portable device

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CEDAR for Windows
CEDAR for Windows is a radical departure in audio restoration systems
It offers both multi-channel and simultaneous multiple-process
restoration capabilities
It can be used in applications of Windows such as audio preparation for
DVD and surround formats as well as for stereo mastering

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CEDAR for Windows (cont’d)
Declick is an invaluable process
that removes scratches and clicks
encountered in audio files
Console is the tool for audio
restoration process that controls
up to 16 channels

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Dehiss2 includes an algorithm that offers
broadband noise reduction with neither
spectral analysis nor offline processing
Decrackle is the effective process of
removing crackle, buzz, surface noise, and
distortion from the audio

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Phase corrector improves mono
compatibility and stereo imaging, extends
high frequencies, and tightens bass
response of the audio signal
NR-3 v2 is a powerful and flexible noise
reduction system for speech and music
developed for the audio and video industries

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EQ and dynamics provide dynamic
processing and equalization with multiple
processes per channel
Spectral Analyzer analyzes the spectrum
of the audio signal

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Audio File Forensic Tools: DCVST
& Advanced Audio Corrector
Advanced Audio Corrector removes
phase distortions in high-quality audio
files before coding it to MP3 format
DCVST is a plug in based on the (AFDF)
Automatic Forensic Adaptive Filter that is
found in the Continuous Noise Filter DC
LIVE/Forensics

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Audio File Forensic Tools:
Acoustica & Smaart
Acoustica is an ideal solution for audio
editing and mastering which records, edits
and processes audio on the system
Smaart is a software designed for real-
time sound system measurement,
optimization and control software for
Microsoft Windows and Mac operating
system

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Audio File Forensic Tools:
DNS1500 & DNS2000
DNS1500 Dialogue noise suppression
suppresses noise content from recordings or
live surveillance and curbs excessive
reverberation
DNS2000 Dialogue noise suppressor
removes background noise from recordings
and live transmissions

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Audio File Forensic Tools: DNS
3000
DNS 3000 is an automated dialogue noise suppression with scenes, memories,
moving faders, and pro-tools integration
• On-board scenes with a simple and intuitive recall
system
• Automation to LTC time code
• Moving faders and sample rates up to 96kHz
• Ensures that there is no loss of lip-sync
• Eliminates all manner of noises from recordings and
live transmissions
Features

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Audio File Forensic Tools: M-Audio
MicroTrack 2496 & CARDINAL
M-Audio MicroTrack 2496 is a rugged
high-fidelity mobile 2-channel digital
recorder that records WAV and MP3 files to
CompactFlash or microdrives
CARDINAL is the next generation forensic
audio processor

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Audio File Forensic Tools: JBR 4 Channel
Microcassette Playback/Transcriber Unit
& JBR Universal DVD/CD Player/Transcriber
• It is designed to safely and accurately play all known ¼ track stereo and ½-track
monaural micro-cassette recordings
JBR 4 Channel Microcassette Playback/Transcriber
Unit
• It is designed and optimized for playing and transcribing all CDs and DVDs
• It enhances the efficiency and accuracy of the transcriber
JBR Universal DVD/CD Player/Transcriber

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Summary
Audio Forensics is the appellation for the engineering discipline involving the analysis, evaluation, and
presentation of acoustic evidence in a judicial inquiry normally leading towards a presentation in court
Voice comparison standards involve evidence handling, preparation of exemplars, copies, and
spectrograms, preliminary examination, and spectrographic analysis
Integrity verification of the audio is necessary to qualify or disqualify the tape for further proceedings
Sound recordings are presented as evidence in court proceedings
Audio forensics involves various methodologies that are enhanced for gaining audibility and intelligibility
of the audio
DCLive Forensics is the audio forensics tool that analyzes, enhances, and improves difficult recordings
using a system with a sound card

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