CS255801B1 - Wiring to remove unwanted signals from the communication channel - Google Patents

Abstract

The solution is in the field of electronics, respectively. Communication Technology. The aim of the connection is to remove unwanted signals - - noise during speech acquisition in noisy spaces by a microphone, which is achieved by connecting two microphones to the preamplifiers whose outputs are connected to the input of the differential amplifier, where the input of the synchronization block is output to one of the preamplifiers. connected to the second preamp input. The wiring is particularly suitable for speech in noisy spaces.

Description

BACKGROUND OF THE INVENTION The invention relates to a circuit for removing unwanted signals from a communication channel when sensing a desired signal by an acoustic-electric transducer-microphone in a noisy environment.

So far, this problem has been solved using microphones or amplifiers with a high lower cutoff frequency. With this method, the noise is only imperfectly eliminated and the bandwidth of the transmitted frequency band is reduced.

Gradient microphones with directional characteristics are used either with or without a common membrane. These microphones require exact match of physical properties of both sensing systems and consequently exact and demanding production of these systems. In addition, the signals are not fully read, especially for higher frequencies.

In addition, so-called throat microphones are used to capture the vocal cords directly. This method is only applicable to speech capture. Furthermore, hygiene problems arise in operations with high dust and temperature, or when different persons are to work alternately with the device.

Using throat microphones is often inconvenient.

The present solution consists in that the acoustic signal is sensed by two microphones 1 and 3. The output signals from the microphones are amplified in the preamplifiers 2 ^and A ^and subtracted from each other in the differential amplifier J5. The microphone I is synchronized by the output signal from the sync block 6, the input of which is connected to the output of the preamplifier 4. One of the microphones is located in close proximity to the acoustic signal source to be transmitted by the communication channel. signal - noise. The second microphone is placed near the first so as to pick up as little as possible of the unwanted signal.

Compared to previously used methods of removing unwanted signals from the communication channel, using the method described above, the unwanted signals are removed more completely without limiting the bandwidth. There are no specific requirements for microphone system conformity and manufacturing accuracy. The device is cheap and simple, easy to apply. There are no hygienic problems.

The drawing shows an example of a specific circuit for speech acquisition in noisy environments. The two microphones i and 3 preferably of the same type are located in a plane at a distance of 5 to 10 cm from each other, for example on a rod attached to the headphones. The microphone axes are parallel. The signals from both microphones are amplified in preamplifiers 2 and with Aj (j w | and Aj (jtu) transmission, where

And is the transmission j - imaginary unit t - angular frequency.

The transmission sensitivity A ^ (jtU) and A. (jdi) can be used to compensate for different microphone sensitivity.

Both signals are subtracted from each other in differential amplifier 5 with transmission A. (jui)

A ₃ (JM) = ^{Uv Y} .tupní. (T) ^at the input differential (t) where u is the voltage t - time at whose output is no longer present an unwanted signal.

The phase difference of the signals from the two microphones caused by the different attenuation of the oscillating microphone systems, i.e. not by exactly the same embodiment of the two microphones, is eliminated by engaging a synchronization block whose input is connected to the preamplifier output 6 and the output to the microphone output. The synchronization member may have. such as transmission

A. (jcu) = k. -A ₂ (jud) where k is a constant determining the degree of synchronization. The microphone 1 is thus forced to vibrate in phase with the microphone 2. If microphones with pencil or octal characteristics are used, that is, microphones sensitive only to the signal coming in the microphone axis, then all acoustic signals incident on both microphones are subtracted. Using microphones with, for example, spherical characteristics would not compensate for signals coming in a direction perpendicular to the microphone axis due to the distance of both microphones and the limited speed of sound propagation and the resulting time delay of the electrical signals from one and the other microphone.

If we place the microphone 1 in front of the mouth of the speaker, the microphone 2, due to its location and characteristics, does not pick up the acoustic signal that we want to transmit and thus does not subtract this signal.

This principle can be used, in particular, to record speech in noisy environments such as factory halls, where the noise level often exceeds the level of useful signals. It can also be used, for example, to prevent unwanted acoustic feedback and to sense non-acoustic signals in environments where undesirable types and frequencies of interference occur.

Claims (1)

A circuit for removing unwanted signals from a communication channel when recording speech in a noisy environment by microphones characterized in that the output of the first microphone (1) is connected via a first preamplifier (2) to the first input of a differential amplifier (5) a second preamplifier (4) connected by its input to the output of the second microphone (3), the output of the second preamplifier (4) being connected to the input of the sync block (6), which is output to the output of the first microphone (1).