PROTECTING SPEECH INFORMATION USING ACTIVE SOUND CANCELING SYSTEMS

Abstract

Usually, to eliminate the leakage of information through
the acoustic channel, either sound insulation or generators
of correlated acoustic noise are used. In the first case
(passive method) requires a significant amount of time to
carry out sound insulation work. In the second case the presence of noise generators creates discomfort during negotiations. The radiation itself is an unmasking sign, which makes it easier for attackers to determine the time and place of negotiations. The disadvantages of both of the above methods can be reduced by using active noise reduction systems (Active Noise Control, Active Noise Cancellation, ANC, Active Noise Reduction, ANR). Such active noise reduction systems are
based on the process of wave interference. Despite the
fact that the method itself allows you to effectively suppress ambient sounds, real devices do not always cope
with this task, especially with acoustic vibrations with a
frequency of more than a thousand Hertz. The fact is that
it takes some time for the microcontroller to register the
sound and calculate the opposite wave. Because of this,
the sound it produces is no longer completely opposite to
the incoming sound, but lags behind it in phase. This
disadvantage can be reduced if the signal to be suppressed
is applied to the input of such a device via an electrical or
electromagnetic channel. Due to the fact that the electrical signal spreads faster than sound, the device starts to
process the signal even before it comes in the form of an
acoustic wave. The noise reduction of such systems works
for sounds with a frequency of up to 4 kHz, which is
quite acceptable for the spectrum of speech information.
Thus, at the boundaries of the controlled area, it is possible to reduce the level of acoustic waves from the sources
of confidential information to a safe value. Such systems
can be successfully used in secure rooms, where the circulation of acoustic (speech) information is generally prohibited.