Examination of phonograms for the presence/absence of signs of editing as a task of expert diagnostics.
Examination of phonograms for the presence/absence of signs of editing as a task of expert diagnostics
The examination of phonograms for the presence/absence of signs of editing or changes made during or after recording is one of the main diagnostic tasks of forensic phonography.
Let us recall that according to [1], such studies as determining the actual state of an object, including the presence or absence of deviations from a certain norm or previously recorded state of the object; determining the causes and conditions of changes in the properties (state) of an object; determining the presence of a trace; determining the possibility of judging the mechanism and circumstances of an event based on its results; establishing a causal relationship between actions and the ensuing consequences, etc. are diagnostic.
Experience in expert practice shows that in fact any investigator's ruling or court ruling on the appointment of a forensic examination of sound recordings raises the issue of editing the presented phonogram.
Since the concept of editing includes intent (the determination of the presence of which, we note, is not within the competence of the forensic expert), the expert has the right to answer only the question about the presence/absence of signs of editing or changes made during or after recording on the soundtrack.
Let us stipulate that in reality, the integrity of a soundtrack may be violated for a number of reasons and often may not have any intention. For example, during another listening to a sound recording, the operator-user may inadvertently turn on the tape recorder to record instead of turning on the playback mode, which always leaves new traces on the original soundtrack.
Discussing various aspects of sound recording editing, let us recall that editing in cinema is understood as “a creative and at the same time technical process in the creation of a film … interpretation of the filmed footage by selecting, combining individual pieces of the image, or so-called editing frames” [2].
The difference between editing in film, television and radio broadcasting and editing in forensic examination of sound recordings is, first of all, that if in the first case editing acts as a completely legal artistic technique, then in the case of using a sound recording as material evidence in criminal or civil proceedings, editing is a means of falsifying the said sound recording.
At the current stage of development of the type of examination we are considering, the task of detecting signs of editing is becoming the most problematic. This situation is associated with the rapid spread of digital formats for recording audio information and the rapid development of computer technologies, in particular modern multimedia tools.
What should be understood by editing in forensic examination of sound recordings?
According to [3], editing should be understood as “the combination of two or more parts of one or more previously recorded phonograms by re-recording, during which changes can be made to the recorded information, and the order of fragments can change.”
When classifying the methods of editing, at present, it is appropriate, in our opinion, to talk about mechanical, electronic analog and electronic digital editing methods.
Mechanical editing of a soundtrack is the connection of individual parts of a soundtrack in the required order by gluing or splicing them.
Electronic analog editing is editing in which editing transitions are formed using analog sound recording equipment.
Electronic digital editing is editing carried out using computer methods through specialized software sound editors using the techniques and means of automated editing.
The concept of selective recording of sound recordings should be especially discussed.
From a technical point of view, selective recording is one of the types of electronic analog or digital (depending on the recording method) editing. The peculiarity of such editing is that the specified editing is carried out during the recording process, and not after it. In fact, the basis of the selective recording technology is a set of successive continuations of the recording of audio information received from the original source.
From the point of view of forensic theory, the examination of a soundtrack for the presence/absence of signs of editing or changes made during or after recording is a complex diagnostic study, which in general should consist of three parts: traceological; auditory-linguistic; instrumental.
Thus, the property of editing of a soundtrack as a document is reflected in diagnostic signs of editing of various groups. The essence of expert examination of a soundtrack for the presence of signs of editing consists in identifying the specified signs of each group, as well as in determining the causes of various violations of the continuity of the recording or other ways of introducing changes into the soundtrack. Based on the identified signs, the expert not only determines the presence of signs of editing on the soundtrack (if any), but also identifies the way in which this editing was carried out.
Without dwelling in detail on the traceological part of the magnetic tape examination in this article, we will only note that not only the magnetic tape (including the geometry of the magnetic tracks on it) should be examined, but also the case of the compact cassette (microcassette, video cassette) in which the tape is placed. The latter is necessary to establish the presence of signs of opening the cassette, if such has taken place. We will explain that cases of opening cassettes are often encountered in expert practice. It should be noted that, generally speaking, the goals of an expert examination provide only for establishing the fact of opening the cassette case, but do not imply finding out the reasons for such an action. The examination of the body of a cassette received for examination acquires special significance in the context of the analysis of a phonogram for the purpose of substitution of the phono-document or its complete falsification, for example, using digital computer editing, which we will discuss below.
If the traceological part of the examination allows us to identify signs of mechanical and electronic analog editing, then the following auditive-linguistic part of the examination can provide significant assistance in detecting signs of not only mechanical and analog, but also electronic digital editing of sound recordings.
The auditory-linguistic part of the study of a soundtrack for the presence/absence of signs of editing can be carried out using both analog and digital sound recording devices, as well as using sound editors included in the specialized software of modern personal computers, which are included in the expert's workstation.
The signs of editing of the auditory-linguistic group may include[1]:
– the presence and location of pulse signals characteristic of transient processes of «on/off» of an analog tape recorder in «recording» mode;
– coherence of the semantic content of conversations recorded on the soundtrack;
– naturalness of the flow of speech acts
(Let us clarify that unnatural, physiologically unjustified sounding of some lines may occur when, as a result of editing, part of the sounding word, phrase or statement is “cut off”. In this case, the remaining part may sound physiologically unjustified. Such a phenomenon may be accompanied by the absence of signs of editing of the instrumental group. In this case, the role of auditive-linguistic analysis increases);
– functional load, adequacy of placement and duration of existing pauses;
– logical and syntactic inconsistencies in the displayed information (in conversations as a whole and in individual phrases);
– changes in the nature of noises in pauses and changes in the nature of background noises during speech acts (acoustic background), stability of background noises;
– adequacy of the intonation structure of speech acts;
– validity/unvalidity of changes in the acoustic depth of sounding remarks.
(It should be noted that changes in the acoustic depth of a sound source can be assessed by both perceptual and instrumental methods);
— inconsistency or lack of limitation in the topic of conversation.
Analyzing the list of features of the auditive-linguistic group, we note that when changing the soundtrack using digital editing methods, the list, or field of possible features, is reduced compared to mechanical or analog editing methods (for example, in the case of digital editing, there are no pulse signals on the soundtrack for turning the recording mode on/off, which are perceived as “clicks” when listening to the soundtrack). But even in this case, most of the features of the auditive-linguistic group remain common to all editing methods.
The importance of the features of the auditive-linguistic group in the technology of expert research is explained by the fact that the essence of the full or partial substitution of a sound document is the change of the original sound information recorded on the carrier. These changes may relate not only to speech or verbal information, but also to the conditions of obtaining the sound record. In what ways can the original sound record be changed?
The main methods of partial change of a sound recording acting as a sound document are erasure, addition, cutting out fragments of the sound recording and editing [3].
Thus, sound recording editing acts as a tool that allows achieving the desired (for the author of the editing) change in the original content of the phonogram. Such a change can be achieved either by any of the above methods or by a combination of them.
In all cases, however, the auditive-linguistic component of the comprehensive study of sound recordings allows identifying places or phenomena that are “suspicious” from the point of view of possible editing and outlining ways to study these facts during the instrumental part of the examination.
It should be taken into account, however, that professionally performed editing is sometimes not detected by ear. In this case, instrumental methods of studying sound recordings come to the rescue [4].
Moving on to the consideration of the instrumental part of the complex diagnostic study of phonograms for the presence/absence of signs of editing, we will explain that the use of modern sound editors in the analysis process allows us to establish a visual connection between the signs of editing of the auditory-linguistic and instrumental groups.
The use of hardware and software for editing and examining sound recordings requires placing the sound recording in the computer's memory, i.e. converting it into a digital recording form.
After placing the sound recording being examined in the computer's memory, an expert armed with a tool with sufficient computing resources for the sound editor and possessing special knowledge in the field of forensic phonography is able to detect traces (signs) of editing.
The following may be attributed to the signs of editing of an instrumental group that may be present on a soundtrack even in the case of using digital electronic editing methods:
– the spectral composition of speech signals and pauses within dialogues;
– the dynamics of the energy level of speech signals;
– the spectral and temporal characteristics of background noises;
(We remind you that in cases where the sections of a soundtrack that are joined during editing have different signal levels, the “fade” function, available in some software editors [5], can be used to hide the traces of editing. In the case of using the “fade” function to hide the editing location, the expert should measure the spectra in the pause sections before and after the supposed editing location, and also evaluate the average speech power in adjacent phrases to the right and left of the joint point);
– spectral-auditory features of the acoustic depth of the spoken lines;
– low-level, parasitic signals of sources and devices accompanying both the primary recording and the procedures associated with possible editing of the soundtrack
(The technology for detecting this feature is that any recording channel leaves its traces in the form of a set of continuous frequencies, sometimes very weak in level, not visually displayed. This does not mean, however, that the specified frequencies cannot be “seen” with the help of some modern sound editors. For example, a break in the phase of a network interference signal (while maintaining the amplitude value) indicates that a fragment of the studied phonogram has been cut out, i.e., that it has been edited [6].
It is interesting to note that, based on the given list of features of the instrumental group, the most effective (from the point of view of detecting traces of editing) are such parameters of the signal recorded on the phonogram that are not perceived by ear at all. These primarily include low-frequency and high-frequency components of the harmonic type: traces of the background of the power supply in the low-frequency region and traces of high-frequency bias of the recorded signal [7]. The latter parameter, however, can be detected far from always, but only on high-quality magnetic tapes and when using a high-class tape recorder.
When analyzing audio information in search of traces of possible editing, it should be taken into account that the signal recorded on the soundtrack additionally reflects not only traces of the equipment used to record and (or) transmit the sound, but also traces of the room in which the recording was made. Special spectral methods implemented in the above-mentioned specialized sound editors are used to isolate and study these traces. By visualizing special features that are essentially carriers of the information required by the expert, specialists with special knowledge in the field of forensic examination of sound recordings can obtain convincing evidence of the presence (or absence) of signs of editing or changes made during or after the recording process on the soundtrack under study.
List of recommended literature
1. Korukhov Yu. G. Trace diagnostics. — M:, VNII SE, 1983. — 76 p.
2. The Great Soviet Encyclopedia. Volume 16. — M: Publishing house «Soviet Encyclopedia»., 1974. — 615 p.
3. GOST 13699-91 Recording and reproduction of information. Terms and definitions. M:, 1991.
4. Kaganov A.Sh. Research of phonograms for editing — problems and solutions. Kharkov: Research Institute of SE named after Bokarius 2004. (in press).
5. R. Yu. Petelin et al. Cool Edit Pro 2 Secrets of craftsmanship. — St. Petersburg: Arlit., 2002. — 432 p.
6. Ivanov I.L., Popova A.R. Issues of expert practice of forensic examination of sound recordings – 14 p.
7. Zhenilo V.R. Computer phonoscopy. M.: Academy of the Ministry of Internal Affairs of Russia, 1995. – 207 p.
[1] Soviet Encyclopedic Dictionary. – M., 1979. – p. 863.
[2] It seems more accurate to talk about the vocal folds rather than the vocal cords, since anatomically the vocal cord is just a thin membrane running along the edge of the vocal fold.
[3] The relative range of change in the fundamental tone frequency D is taken to be the value equal to the ratio of the maximum value of FOR (the average value of FOR plus twice the standard deviation) to the minimum (the average value of FOR minus twice the standard deviation).
[4] The relative deviation is understood as the modulus of the difference between the average FOR of the original and comparative recordings, divided by the value of the average FOR of the comparative recording.