SU1499525A1 - Compensator for multiplicative distortion of signals for systems with acoustic feedback - Google Patents

Abstract

The invention relates to radio engineering. The purpose of the invention is to improve the accuracy of compensation. The compensator contains an amplifier 1 with a variable coefficient. amplification, amplitude detector 2, low pass filters 3 and 4, adders 5 and 6, divider 7 signals, reference source 8 and frequency shift block 9. The goal is achieved by introducing a filter 4 and an adder 6, with which the multiplicative interference due to the circulation in the loop of the acoustic feedback of frequency-shifted signals is fully compensated. 1 il.

Description

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The invention relates to radio engineering and communication, and can be used in sound amplification devices in the presence of acoustic feedback between a microphone and a loudspeaker.

The aim of the invention is to improve the accuracy of compensation.

The drawing shows the structural electrical circuit of the multiplicative signal distortion compensator for systems with acoustic feedback.

The compensator contains a variable gain amplifier 1, an amplitude detector 2, first 3 and second 4 low pass filters, first 5 and second 6 adders, divider 7 signals, reference source 8 and frequency offset unit 9.

The multiplier signal distortion compensator for systems with acoustic feedback works as follows.

Let the compensator work in a circuit amplifying the signal of the form

U (t) (t) cosw (t),

where v (t) is the sound signal envelope

w (t) is the instantaneous frequency of the audio signal.

If the signal U (t) is speech, then the envelope y (t) characterizes the pitch of the speech signal. The fundamental tone Wj is defined as the instantaneous frequency of the time envelope of the signal and lies in the range 70-330 Hz. As a result of frequency conversion in block 9, the signal at the output of the sound amplifying system takes the form

U, (t) K (t)) 4t) + t “, (t), where Wi is the magnitude of the frequency shift.

After the time required for the sound from the loudspeaker to the microphone to pass through the acoustic feedback circuit, a signal is set at the input of the amplification system, equal to the sum of the input signal and the signal input to the feedback circuit:

U, (t) Kpco, (t - -0),

where K is the gain of the sound amplifying system without acoustic feedback;

f is the coefficient characterizing the attenuation of the signal during its propagation from the loudspeaker to the microphone; i is the delay time of the signal during its propagation from the loudspeaker to the microphone. For minor delays (which is almost always the case), we can assume that v (t) v (t - L), while

u, (t) + Kf / co, (t - -d)

 y (t) M (t) (t) + + (Vi (t) -t- V (t) 1,

(one)

5 20

25

thirty

 .,.

45

50

where M (t) is the coefficient characterizing the multiplicative distortions caused by the circulation in the loop of the acoustic feedback of frequency-shifted signals;

((t) are phase distortions associated with the circulations in the loop of the acoustic feedback of frequency shifted signals. If v (t) is represented as

(t) ha + VJ (t),

where m is the average envelope

speech signal J J is the deviation of the envelope of the speech signal impressed in the amplitude detector 2 from the average value, the instantaneous frequency of which is equal to the frequency w of the fundamental tone, then the output of the first filter 3 decreases the signal the cutoff frequency of the first filter 3 satisfies the relation σ, cp1 Wj, and at the output of the second filter 4, a signal equal to S, j (t) mM (t), since its cutoff frequency satisfies the relation uJcp - f the first 5 and second 6 adders signals are respectively

S / t) + s / m h / s;

S (t) + (f M (t) + T, and the signal at divider 7 is determined by

)

S (t) + cf

d + u

rnMCty with

(2)

where tf is the signal level at the source output 8 (/) and “/“ S (t)).

For an eG satisfying the given relations, equality (2) takes the form

(MSEU

So after multiplying. signal (1) to signal (3) at the output of amplifier 1 have

y (t) M (t) X (t) (t) +

+ u), (t) + v (t) -j. (t) (t) +

+ tOi (t) +4 (t) 3,

those. the multiplicative interference M (t) is completely compensated. Moreover, even if the signal at the output of the second filter 4 is zero (m 0), then the problem of dividing by zero does not arise.

Claims (1)

Invention Formula A multiplicative signal imperfections compensator for acoustic feedback systems, containing a variable gain amplifier, a reference voltage source and a series-connected amplitude detector, the first Q low pass filter, first adder and signal divider, characterized in that, in order to improve the accuracy of compensation, serially connected 15 second low pass filter and second adder, the output of which is connected to the second input of the signal divider, the output of which is connected to the control input of the variable amplifier 20 by the gain, the output of which is connected to the input of the amplitude detector, the output of which is connected to the input of the second low-pass filter, and the second inputs of the first and second adders are combined and connected to the output of the reference voltage source.