Table of vectors of identification features of changes in video and audio recordings made during or after recording on digital storage media..
Table of vectors of identification features of changes in video and audio recordings made during or after recording on digital media.
Based on materials from:
Philological Faculty of the Moscow State University named after M.V. Lomonosov
(laboratory of phonetics and speech communication and center of speech technologies),
International conference «Functional styles of sounding speech» 05.09.05 -07.09.05.
Ivanov I.L.
Russia
Introduction:
Rapid development of scientific and technical progress related to the development of a wide range of devices for documenting audio-video information on digital media opens up new research areas for forensic video phonography. These areas often intersect with research in the field of high technologies related to forensic computer-technical research. To understand this problem, statistics on the presentation of research and comparative material for video phonographic research for the period 2004 — early 2005 were summarized.
Table No. 1.
| Source material | Comparative material | |||
|
Magnetic recording |
Digital recording |
Magnetic recording |
Digital recording |
|
| 2004 |
21 |
3 |
17 |
0 |
| from 01 to 04 2005 |
0 |
4 |
4 |
0 |
Thus, an irreversible trend of transition to digital devices for documenting the source material is revealed. The study of comparative identification material presented for the beginning of 2004 led to the unambiguous statement that it was also initially in digital form and then recorded on magnetic tape.
Directions of research:
1. Establish all transformations that occurred with the object of documentation (visual image or sound wave of the original speech) in the reflection of information that was received for research.
2. Having previously examined the presented material and explanations to it from the criminal (civil) case or from the words of the customer of the research, determine the conditions of the original recording, characteristics of the documentation device, the surrounding environment, in the process of documentation. If necessary, send the appropriate requests.
3. In case of providing a documentation device for research – study all tactical and technical data of the device.
4. Decide on the direction of the feature vector that must necessarily accompany this documentation process and also determine the feature vector that must be absent in the material submitted for research.
5. Conduct a trace, audit, instrumental study to identify features and compare with those feature vectors that were initially formed for the research.
6. In the synthesizing section, conduct a full analysis of the identified and missing features.
The source material, initially documented in digital form of presentation of analog information, can be presented for research most often in the following forms:
1. On a laser compact disc, flash memory, magnetic diskette, etc. in the form of an audio-video file.
2. In the form of a video-audio file inside a documentation device (cell phone, digital camera, digital voice recorder, etc.).
3. On magnetic tape with digital recording.
4. On magnetic tape with analog recording (the original digital stream is converted to analog form).
At the beginning of the study, it is extremely important for the expert to understand all the changes that occurred associated with the transformation of the documented object (visual image or sound wave of the original speech) into the reflection of the information that was received for the study. Incorrect understanding of this problem, non-compliance of the workplace with the requirements for this type of research, and sometimes lack of work experience often does not allow you to correctly answer the questions posed. Reflection of the recording channel in the material presented in the study allows you to unambiguously determine the features at the level of visual-auditory-instrumental and abstract research. For this, we will consider a generalized scheme for searching and compiling a table of feature vectors. In parallel, we will form the feature vectors of those present and absent in the properties of the material under study.
Traceological examination
|
Visual level |
Visual-auditory level |
Feature vectors in the recording channel |
|
| Inspection of magnetic tape, magnetic surface of a floppy disk or compact disc | 1. Integrity of the case. 2. The presence of a screw/adhesive connection and its condition. 3. Traces of disassembly of the case. 4. The quality of the watering and the condition of the active surface of the carrier. 5. Traces of scratches and crumbling of the active layer. 6. Deformation of the active layer or its carrier. |
1. Determination of the time compliance with the detected changes of the visual level. | 1. Acceptability/inadmissibility of the presence of changes in the original record associated with the changes detected by the visual level. |
Microphone, first input amplification stages
|
Auditory level |
Instrumental level |
Feature vectors in the recording channel |
|
| Location of the documentation device, acoustic environment | 1. Fixed/movable. 2. Protected/unprotected. (hidden under clothing, in a bag, side pocket, etc.). 3. Acoustic environment near the microphone: room, street, field, forest, car cabin, highway, etc. 4. Presence of wind signs, drop/rise of high frequencies. Characteristic signs of object movement (steps) and associated periodic noises of clothing, etc. 5. Signs of a telephone conversation (cell phone, regular phone). 6. Presence of background noise in the form of melodies/songs, etc. 7. Presence/absence of room echo |
1. Decrease/increase in frequency response. 2. Identification of signs of reflection in the source material of the surrounding electromagnetic environment. 3. Signs of transmission/reception of a cell phone. 4. Limitation of the spectrum of the telephone channel (0.3-3.4 kHz). 5. Presence/absence of harmonic interference that penetrated the recording channel. 6. Presence/absence of pulsed periodic/non-periodic interference that penetrated the recording channel. 7. Measuring background music/song by duration. 8. By echo duration — assessment of the room volume, its reverberation properties |
1. Admissibility of the presence/absence of 50Hz and multiples of it harmonic components. 2. Admissibility/inadmissibility of spectrum limitation in the low and high frequency range. 3. Admissibility/inadmissibility of the presence of periodic/non-periodic impulse interference. 4. Acceptability/inadmissibility of the presence of radio channel clipper noise in the recording channel. Radio channel loss in case of object movement/immobility. 5. Acceptability/inadmissibility of the presence of loss of synchronization, color, video sequence, audio sequence in the video sequence. 6. Acceptability/inadmissibility of changing the duration of background music/song, etc. and, the possibility of comparison with the duration of the original music/song. 7. Acceptability/inadmissibility of the presence of echo and its duration. |
Documentation device and its software
|
Abstract level |
Instrumental level |
Feature vectors in the recording channel |
|
| Information provision formats | 1. Analysis of all formats: sampling frequency, bit rate, compression formats. 2. Memory capacity and the associated maximum possible length of audio and video files. |
1. Visual assessment of the spectral density of the compression format and side effects associated with it. | 1. Acceptability/inadmissibility of presenting information in the format of the original material.
2. Acceptability/inadmissibility of the presented compression algorithm |
| Documentation device software | 1. Possibility of editing: deletion, modification, overlay, etc. by means of the documentation device or its software 2. The ability to record external information into the device. 3. The ability to transmit or receive it from another source other than its own software |
1. Testing the capabilities of the abstract level. 2. Researching the internal format of information presentation and the format of downloaded digital information. 3. Researching the binary information of the structure of an audio/video file. 4. Search for stable signs related to programmer errors or the peculiarity of the structure of binary presentation in the form of files. |
1. Acceptability/inadmissibility of changing the source material. 2. Acceptability/inadmissibility of deviations from the standard binary structure of internal information in the file. |
| Control record. | 1. Study of the frequency response, harmonic/non-harmonic interference entering the recording channel regardless of the acoustic channel. 3. Evaluation of changes in interference over time (frequency drift, quartz stabilization of harmonics) 2. Evaluation of the immunity of input circuits from electromagnetic interference. 3. Identification of traces of aliasing in the operation of the ADC of the documentation device. 4. Measurement of the dynamic range. 5. Evaluation of nonlinear distortions. 6. Study of the frequency response of the recording channel. 7. Evaluation of detonation signs. |
1. Acceptability/inadmissibility of the correspondence of the features of the instrumental group on the control recording and the research material. 2. Acceptability/inadmissibility of the presence of harmonic and non-harmonic interference, recording channel overload in the source material. 3. Identification of mandatory features that must be present in the source recording. |
Visual-auditory-instrumental study
|
Visual-auditory level |
Instrumental level |
Feature vectors in the recording channel |
|
| Study of the behavior of the amplitude, frequency, phase of the harmonic components identified in the original recording | Auditory comparison of changes in the acoustic environment with the instrumental level. | 1. Identification of signs of phase breaks, changes in frequency, and the level of the harmonics under study. 2. Study of secondary phase and amplitude-frequency modulation. 3. Checking the continuity of the recording in case of changes in the audit level of the study. 4. Checking the durations of background music/songs and other known or calculated durations of the background environment. 5. Determining the exact nodes of the time duration based on the background environment. |
1. Acceptability/inadmissibility of changes in the amplitude, frequency, phase break of harmonic components present in the original recording. 2. Study of the identified feature vectors that are necessarily present/not permissibly present in the original recording. 3. Permissibility/inadmissibility of deviations from fixed-duration time nodes. |
| Study of video and audio sequence. | 1. Correspondence of video sequence to audio sequence. 2. Detection of interframe and intraframe editing. 3. Detection of video sequence artifacts. |
1. Storyboard of video recording. Definition of continuous scenes. 2. Restoring the editing table of transitions in the production of a video recording. 3. Restoring continuous scenes of video and audio. |
1. Acceptability/inadmissibility of changing synchronization, color, audio within scenes and between scenes. 2. Acceptability/inadmissibility of correspondence/non-correspondence of the video sequence to the audio sequence. |
Borderline computer-technical research
|
Instrumental level |
Feature vectors in the original record |
|
| Study of the internal binary structure of the record under study and its comparison with the declared documentation device or with the software supplied with the documentation device. | 1. Study of the header format, internal structure of data placement, service information. 2. Correlation of the identified features to the recording device, or its model, or to the software supplied with the recording device. |
1. Acceptability/inadmissibility of deviations from the declared internal format of information presentation to the format of the original recording. |
Synthesizing part
Based on the study of the generated conformity/non-conformity vectors, determine:
1. Acceptability of their presence/absence in the original recording.
2. Determine whether the material submitted for examination is the original or a complete copy of the original.
3. What changes did the original signal undergo.
4. Admissibility/inadmissibility of the identified changes.
5. Justify: did the identified changes occur during the recording process or after?
Literature
1. Kaganov A.Sh. Modern methods, hardware and software used in forensic examination of sound recordings. Moscow 2003.
2. Kaganov A.Sh. Forensic examination of sound recordings. Moscow 2005
3. J. Barnes Electronic design: methods of combating interference Mir 1990
4. Shinakov Yu.S. Kolodyazhny Yu.M. Fundamentals of radio engineering Moscow 1993
5. Losev A.K. Theory of linear electric circuits Moscow 1987
6. Sibert U.M. Signal circuits of the system part 1.part 2. Moscow 1998
7. Danilov A.V. Matkhanov P.N. Filippov E.S. Theory of Nonlinear Electric Circuits Leningrad 1999.
8. Kintzel Tim. Programmer's Guide to Working with Sound Moscow 2000.
9. Kaganov A.Sh. On Mathematical Models of Expert Identification and Diagnostics //Expert Technology. Issue 125: Study of Video and Sound Recordings. — M., VNIISE under the Ministry of Justice of the USSR, 1995.
10. Mailis N.P. Technology of Expert Research //Modern Methods, Hardware and Software Used in Forensic Examination of Sound Recordings. Methodological Manual for Experts/edited by A.Sh. Kaganov — M.: RFC SE under the Ministry of Justice of Russia, 2003.