Electronic devices for intercepting information: digital voice recorders.

Electronic devices for intercepting information: digital voice recorders.

KHOREV Anatoly Anatolyevich,
professor, doctor of technical sciences

Moscow State Institute of Electronic Technology
(Technical University), professor

ELECTRONIC DEVICES FOR INTERCEPTING INFORMATION: DIGITAL VOICE RECORDS

Source: magazine «Special Equipment and Communications»

An overview of modern digital dictaphones is provided as the most accessible and widespread means of acoustic intelligence.

An overview of modern digital dictaphones is provided as the most accessible and widespread means of acoustic intelligence.

Digital voice recorders are used mainly to record confidential conversations held in office premises. They can be used by persons who have at least short-term access to these premises. In addition to employees of the company (enterprise, institution), such persons may include employees of various services that service the technical means and equipment of the company (security and fire alarm systems, air conditioning, communications, computer equipment, etc.), cleaners and even visitors who periodically visit the office premises.

Digital voice recorders are secretly installed in the interiors of premises, usually immediately before a closed event. They can be camouflaged as everyday objects, such as books, writing instruments, cigarette packs, etc. After the event, the voice recorder is removed from the premises.

Currently, foreign and domestic companies produce a huge number of portable digital voice recorders in both standard and miniature designs, which are very easy to hide in almost any room.

Voice recorders are available in plastic and metal cases. The advantage of portable digital voice recorders made in a metal case is that they are practically impossible to detect with voice recorder detectors and suppress with voice recorder suppressors.

Modern portable digital voice recorders are equipped with built-in and/or miniature remote microphones, have automatic recording level adjustment (dynamic range from 60 to 90 dB), voice recording control (VAS), allow recording time, duration of conversation, etc.

The sampling frequency of the speech signal is from 8 to 64 kHz or more. In this case, the frequency range can be from 20 — 200 Hz to 4 — 20 kHz. Voice recorders have built-in memory from 128 MB to 2 GB or more, allowing continuous recording for several days.

Table 1 shows the average recording time in different modes with a memory capacity of 1 GB [7].

Table 1. Average recording time in
different modes (memory capacity of 1 GB)

Note: The recording time with data compression is given in brackets.

The battery life of digital voice recorders depends not only on the memory capacity, but also on the battery capacity. With a larger voice recorder, you can install a battery with a higher capacity and, therefore, provide more continuous recording time.

Typical portable compact digital voice recorders include the Edic-mini series voice recorders, the appearance of some of them is shown in photos 1–5, and the main characteristics are in tables 2–5 [2].

a – Edic-mini A1

b – Edic-mini LCD B8
Photo 1. Digital voice recorders of the Edic series:

Photo 2. Digital voice recorder Edic-mini Tiny A22

Photo 3. Digital voice recorder Edic-mini Tiny B21

a – Edic-mini Tiny 16 B25;

b – Edic-mini Tiny B22

Photo 4. Digital voice recorders Edic-mini Tiny

Photo 5. Digital voice recorder Edic-mini Tiny 16 B26

Voice recorders are available in both plastic and metal cases. They are small in size and weigh from 6 to 28 g. Despite their small size, voice recorders provide continuous high-quality recording for a day or more.

Let us consider the main features of compact portable digital voice recorders using the example of the Edic mini Tiny B22 series voice recorder, the appearance of which is shown in photo 1b [2]. The voice recorder has a metal case and with dimensions of 31-25-6 mm weighs only 13 g. The voice recorder is powered by a standard CR2016 battery with a voltage of 3 V. The maximum continuous recording time (sampling frequency 8 kHz, without compression) from a fully charged battery is about a day. The voice recorder has a built-in clock and calendar, password access protection, a voice activation system, a timer for starting recording at a specified time, a digital signature of the recording made, and other features. The built-in microphone provides high-quality recording at a distance of up to 7–9 m.

Table 2. Main characteristics of the Edic-mini series digital voice recorders

Table 3. Main characteristics of the Edic-mini series digital voice recorders

Table 4. Main characteristics of the Edic-mini series digital voice recorders

Table 5. Technical characteristics of the Edic-mini Tiny series voice recorders

The recorder has the ability to perform linear and/or ring recording. With linear recording, the number and duration of messages are limited only by the amount of free memory. The maximum recording duration (sampling frequency: 8 kHz, without compression) is from 4 to 240 hours, depending on the model. When using different compression algorithms (logarithmic, ADPCM 4- and 2-bit), the recording time can be increased by 1.25 — 5 times. The ring recording method allows you not to stop recording when the recorder runs out of free memory; the recorder simply starts replacing old data with new data.

To protect information in the recorder, it is possible to set a password that prohibits another user from accessing the recorder's contents and settings. Each recording made by the recorder has a time and date stamp of the start of the recording, and is provided with a digital signature that allows you to determine which recorder was used to make the recording and whether the recorded file was modified. The recorder has an automatic recording mode by timer: daily (the start and end times of the recording are set) and one-time (the date «start time» and the date «end time» of the recording are set).

The voice recorder is equipped with a voice activation system (VAS — voice activation system), which reduces memory consumption (thus increasing the actual recording time) and energy consumption from the power source. When using this system, memory is saved during pauses, but time intervals are saved. When loading records into a PC, the duration of pauses can be restored (as silence) or skipped depending on the settings made. The voice recorder is controlled by one button (start/stop recording) or a switch, depending on the model. The voice recorder's operating modes are indicated by an LED. Using the cable included in the delivery set, the voice recorder is connected to the USB port of the computer. The built-in USB interface provides an information exchange rate with a PC of up to 5.5 Mbaud.

The included software, running under Windows 2000/XP operating systems, allows you to save recorded messages as standard audio files, program various recorder parameters, and use the recorder as a flash drive to store and transfer files ranging from 128 to 2048 MB depending on the model. The Edic-mini series also includes recorders with a relatively long continuous recording time. For example, for the Edic-mini Tiny 16 B26 recorder, this time is 360 hours.

Along with conventional digital voice recorders, special professional voice recorders can be used for covert recording. Such voice recorders are made in a shielded case, have small dimensions and weight. They allow recording in both mono and stereo modes. The recording can be encrypted using various algorithms. The settings of the operating modes of such voice recorders are made using a personal computer. As a rule, there are only a few LED indicators and an on/off switch on the body of the voice recorders. Such recorders include, for example, the DSR CoE M, DSR CoE S and VIC 280 R recorders (photo 6) [4, 7].

a – DSR CoE M (miniature — 10×51.1×18.7 mm) and DSR CoE S (standard − 12×51.4×30 mm);

 б –VIC 280 R

Photo 6. Miniature digital voice recorders with a memory capacity of 1 GB:
 

The VIC 280 R digital voice recorder has a memory capacity of 128 MB to 1 GB. The built-in Li-Ion battery (180 mAh) provides continuous recording at a speed of 20 to 80 kbps for 7 hours. The dynamic range of the audio signal is 60 dB [4].

The DSR CoE S digital voice recorder has dimensions of 12-51.4-30 mm; memory capacity of 1 GB; frequency range — from 20 Hz to 12 kHz; signal sampling frequency from 6 to 24 kHz; recording mode – mono/stereo; recording time in mono mode – from 6 to 48 hours. The voice recorder is powered by an AAA battery. Operating time from an AAA battery is at least 20 hours [7].

Professional digital voice recorders are also available in camouflage design. Most often, such voice recorders are built into a pen, wristwatch, keychain, lighter, etc. (photo 7 – 9) [2, 3, 5, 6].

and − USB-REC (continuous recording time – up to 8 h,
data reset via USB port,
power supply – 3.7 V battery,
 memory — from 128 MB to 4 GB);

б − KEY-R (continuous recording time — 9 h,
information reset via USB port,
power supply — 3.7 V battery, memory — 128 MB;
conversation interception range — up to 5 m)

Photo 7. Digital camouflage voice recorders:
 

a)

b)

c)
Photo 8. Digital voice recorders REG PEN 1 (a), REG PEN 2 (b) and MP3 Voice Recorder Pen (c),
 built into pens (continuous recording time up to 8 h,
 information reset via USB port; power supply – 3.7 V battery; memory 1 – 2 GB)

Photo 9. Digital voice recorder REG ORL, built into a wristwatch
(continuous recording time up to 8 h,
information reset via USB port,
power supply – 3.7 V battery,
> memory 1 – 2 GB)

As a rule, such voice recorders have built-in batteries, providing a maximum continuous recording time of up to 8 — 9 hours. Information is reset via a USB port. In this case, it takes an average of 1 minute to reset an hour of recording.

Literature

1. Khorev A.A. Technical information protection: a textbook for university students/in 3 volumes, v. 1. Technical channels of information leakage.  M.: Scientific and Production Center «Analytics», 2008.  436 p.

2. Professional miniature digital voice recorders Edic-mini and modules [Electronic resource]. – Access mode: http://telesys.ru./products/recorders/index.php.

3. Audio Surveillance [Electronic resource]. – Access mode: http://brickhousesecurity/covert-audio-surveillance.html.

4. Digital Microrecorders: product range. – Italy, Torino, B.E.A. S.r.l., 2007. – Р. 55 – 58.

5. Ricevitori e Mini Registratori Audio [Electronic resource]. – Access mode: http://selavio/prodotti/ricevitori-audio.

6. Security and surveillance products. [Electronic resource]. – Access mode: http://endoacustica/index_en.htm.

7. Surveillance Product presentation [Electronic resource]. – Electronic text, graphic. (662.7 MB). – Denmark, Spectronic, 2007. – 1 electronic optical disc (CD-ROM).