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  1. 1. Module XXII – Audio File Forensics
  2. 2. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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.
  3. 3. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited News: Audio Forensics Experts Reveal (Some) Secrets Source: http://www.wired.com/
  4. 4. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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:
  5. 5. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited Module Flow Audio Forensics Methodologies Fast Fourier Transform Tools Sound Recordings as Evidence in Court Proceedings Audio Forensic Process Why Audio Forensics?
  6. 6. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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
  7. 7. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited Why Audio Forensics? Audio Tape Verification and Authentication Monitoring suspicious criminal targets Audio Tape Enhancement Voiceprint Analysis Tracking missed information Monitoring employees
  8. 8. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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.
  9. 9. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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:
  10. 10. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited FFT Analysis: Screenshot 1
  11. 11. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited FFT Analysis: Screenshot 2 Discontinuities on A’s background B’s Background
  12. 12. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited FFT Analysis: Screenshot 3
  13. 13. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited Methodologies of Audio Forensics Voice identification Audibility analysis Audio enhancement Authenticity analysis Sound identification Event sequence analysis Dialogue decoding Remnant signal analysis
  14. 14. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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
  15. 15. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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
  16. 16. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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
  17. 17. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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:
  18. 18. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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
  19. 19. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited Audio Enhancement: Screenshots
  20. 20. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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:
  21. 21. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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
  22. 22. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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
  23. 23. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited Dialogue Decoding Dialogue decoding is the extraction of the message from the recording It is based upon voice patterns in a spectrograph
  24. 24. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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.
  25. 25. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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
  26. 26. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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:
  27. 27. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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
  28. 28. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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
  29. 29. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited Audio Forensics Process: 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
  30. 30. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited Audio Forensics Process: 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
  31. 31. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited Audio Forensics Process: 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
  32. 32. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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
  33. 33. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited Audio File Formats http://www.fileinfo.net/
  34. 34. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited Audio File Formats (cont’d)
  35. 35. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited Audio File Formats (cont’d)
  36. 36. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited Audio File Formats (cont’d)
  37. 37. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited Audio File Formats (cont’d)
  38. 38. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited Audio File Formats (cont’d)
  39. 39. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited Audio File Formats (cont’d)
  40. 40. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited Audio File Formats (cont’d)
  41. 41. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited Audio File Formats (cont’d)
  42. 42. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited Audio File Formats (cont’d)
  43. 43. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited Audio Forensics Process: 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
  44. 44. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited Audio Forensics Process: 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
  45. 45. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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
  46. 46. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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
  47. 47. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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
  48. 48. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited Tools
  49. 49. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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
  50. 50. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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
  51. 51. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited DCLive Forensics (cont’d) • 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
  52. 52. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited DCLive Forensics (cont’d) • 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
  53. 53. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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
  54. 54. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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
  55. 55. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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
  56. 56. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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
  57. 57. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited CEDAR for Windows (cont’d) 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
  58. 58. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited CEDAR for Windows (cont’d) 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
  59. 59. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited CEDAR for Windows (cont’d) EQ and dynamics provide dynamic processing and equalization with multiple processes per channel Spectral Analyzer analyzes the spectrum of the audio signal
  60. 60. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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
  61. 61. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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
  62. 62. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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
  63. 63. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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
  64. 64. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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
  65. 65. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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
  66. 66. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited 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
  67. 67. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited
  68. 68. EC-Council Copyright © by EC-Council All Rights Reserved. Reproduction is Strictly Prohibited

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