RU2302074C2 - Frequency correction method and automatic device for realization of the method - Google Patents

Abstract

FIELD: technical cybernetics and radio engineering, possible use for building devices for automatic correction of frequency distortions occurring in, for example, sound amplification channels.

SUBSTANCE: method includes comparing spectrum of original signal to spectrum of resulting signal, generated after distorting channel. Comparison results are used for influencing the original signal for changing ratios of its spectrum components. One of variants of the method is to determine normalized spectrums. Two spectrum analyzers, controllable frequency corrector, comparison block and control block are main component parts of the device.

EFFECT: automatic correction of amplitude-frequency distortions introduced by real distorting channel, without usage of special test signal.

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Description

The invention relates to technical cybernetics and radio engineering and can be used in the construction of devices for automatic correction of frequency distortions arising, for example, in sound amplification paths.

Currently, frequency correction is understood to mean compensation of signal distortions arising due to unequal amplification of various parts of the spectrum of this signal. Frequency distortion occurs when a signal passes through circuits whose transmission coefficient depends on the frequency in the frequency range occupied by the useful signal. To eliminate distortion, additional corrective circuits are introduced, the amplitude-frequency characteristic (AFC) of which is selected so that the introduced distortions are compensated, if possible, by additional amplification or attenuation. A rather effective way of frequency correction is an approach based on determining the spectrum of a test signal after it passes distorting frequency-dependent circuits. It is assumed that the spectrum of the test signal is a priori known and does not change. The deviation of the shape of the spectrum of the resulting signal from the horizontal line is judged on the introduced distortions and make appropriate compensating changes in the spectrum of the original signal. The method is implemented in a device consisting of a test signal generator, a controlled multiband amplitude-frequency corrector (hereinafter referred to as the frequency corrector) and a spectrum analyzer (the same as a spectrum analyzer) with a display [Yamaha EQ-550. Natural sound stereo graphic equalizer. Owner's manual, 1999, p. 9]. Since the mentioned device is designed to work with audio signals, the correction is carried out on a test signal that is close in white to noise in the range of audible frequencies in its spectral properties (pink noise is also often used). The test signal reproduced by the speakers at the listening point of the audio programs is received by a measuring microphone and sent to a spectrum analyzer to visually assess the degree of deviation of the spectrum shape of the recorded signal from a straight line. Correction is made manually or automatically by amplifying or attenuating individual frequency components with the help of a controlled frequency corrector that performs the functions of a timbral block, and is controlled by the results of the display of the spectrum analyzer. The disadvantage of this method, adopted for the prototype, and therefore the structure itself, is the need to use a special test signal, which does not allow for frequency correction quickly and automatically on the working signal without allocating time for a special test mode.

The technical result achieved using the present invention consists in the automatic correction of amplitude-frequency distortions without the use of a special test signal.

The technical result is achieved by the fact that in the frequency correction method (option 1), which provides for determining the spectrum of the resulting signal subjected to frequency distortion, according to the invention, the spectrum of the original signal is determined, the spectra of the initial and resulting signals are compared, the comparison results are used to influence the original signal to change the ratios between its spectral components.

The method according to the first embodiment may have features consisting in the fact that:

- the spectra of the source and the resulting signals are compared with each other by calculating the difference of the spectral components corresponding to n points of the spectrum (n is an integer, a finite number);

- the spectra of the source and the resulting signals are compared with each other by calculating the ratio of the spectral components corresponding to n points of the spectrum (n is an integer, a finite number);

- the spectra of the source and resulting signals are spectra of the average rectified values;

- the spectra of the source and resulting signals are energy spectra;

- The spectra of the source and resulting signals are spectra obtained by the discrete Fourier transform method.

The technical result is achieved by the fact that in the frequency correction method (option 2), according to the invention, the normalized spectrum of the original signal is determined, the normalized spectrum of the resulting signal subjected to frequency distortions is determined, the normalized spectra of the initial and resulting signals are compared, the comparison results are used to influence the original signal for changes in the relations between its spectral components.

The method according to the second embodiment may have features consisting in the fact that:

- the normalized spectra of the initial and resulting signals are compared with each other by calculating the difference of the spectral components corresponding to n points of the spectrum (n is an integer, a finite number);

- the normalized spectra of the initial and resulting signals are compared with each other by calculating the ratio of the spectral components corresponding to n points of the spectrum (n is an integer, a finite number);

- the normalized spectra of the initial and resulting signals are spectra of the media of non-rectified values;

- the normalized spectra of the source and resulting signals are energy spectra;

- the normalized spectra of the source and resulting signals are spectra obtained by the discrete Fourier transform method.

The technical result is also achieved by the fact that in an automatic device that implements the method according to the first embodiment, containing a spectrum analyzer of the resulting (output) signal and a controlled frequency corrector, the input and output of which serve as the input and output of the device, according to the invention, an initial signal spectrum analyzer is introduced, a unit the comparison unit and the control unit, the comparison unit is used to compare the spectra of the source and the resulting signals obtained using spectrum analyzers, the control unit serves to directly control the frequency corrector according to the results of comparing the spectra of the initial and resulting signals.

The technical result is also achieved by the fact that in the automatic device that implements the method according to the second embodiment, containing a controlled frequency corrector, the input and output of which serve as the input and output of the device, according to the invention, an analyzer of the normalized spectrum of the initial signal and an analyzer of the normalized spectrum of the resulting (output) signal are introduced , the comparison unit and the control unit, the comparison unit is used to compare the normalized spectra of the source and resulting signals obtained with power spectrum analyzer, the control unit serves to directly control the frequency corrector based on the comparison of normalized spectra the input and output signals.

In automatic devices, the signal at the input of the spectrum analyzer of the resulting signal can be supplied directly from the output of the electronic part of the distorting path or, if the acoustic path is distorting, from a measuring microphone installed in the region of acoustic wave reception.

In automatic devices, the controllable frequency corrector can be an electronically controlled multi-band graphic equalizer.

In automatic devices, you can apply a comparison block containing a subtraction block, an adder, an address counter, an address decoder, a group of registers and an OR element, the first input of the subtraction block is the information input of the control block, the reference input of which is the second input of the subtraction block, the output of which is connected to the first the adder input, the second input of which is the offset code input, the adder output is connected to the combined information inputs of the group registers, the clock inputs of the group registers are connected to Resp outputs of the decoder, whose input is connected to the discharge outlet of the counter whose carry output is connected to the first input of the OR gate, the second input of which is the reset input (initial setting) of the comparator, a clock input of the counter is a clock terminal of the comparator, the output of which are the output of register group.

The invention is illustrated by graphic material.

Figure 1 shows a functional diagram of an automatic device for correcting frequency distortion with a connected distorting path; figure 2 shows graphs illustrating a method of frequency correction; figure 3 shows a functional diagram of one of their possible options for the joint implementation of the comparison unit and the control unit.

The functional diagram of figure 1 contains a device for correcting frequency distortion, including a frequency corrector 1, spectrum analyzers 2 and 3, a comparison unit 4 and a control unit 5. In addition, figure 1 shows the distorting path 6. The input of the device is the input of the frequency corrector 1, N control inputs of which make up a single N-channel input and are connected to the corresponding outputs (single control output) of the control unit 5, the information input of which is connected to the output block 4 comparison, to the first and second information inputs of which the outputs of the spectrum analyzers 2 and 3 are connected, respectively, the information input of the spectrum analyzer 2 is connected to the input of the device, and to the information input of the spectrum analysis Ator 3, the output of the distorting path 6 is connected, the input of which is connected to the output of the frequency corrector 1.

Figure 2 contains a graph of Y ₁ (ω) normalized values of the spectrum of the original signal supplied to the input of the frequency corrector 1 received at the output of block 2; graph Y ₂ (ω) of the normalized values of the spectrum of the resulting signal after path 6 obtained at the output of block 3, ω is the circular frequency.

The functional diagram of FIG. 3 comprises a comparison unit 4 and a control unit 5. In turn, the comparison unit 4 contains a subtraction unit 7, an adder 8, an address counter 9, an address decoder 10, a group of 11 registers 11-1 ÷ 11-N and an OR element 12. The first input of the subtraction unit 7 is the first information input Y ₁ (nΔω) of the unit 4, intended for connection with the output of the spectrum analyzer 2, the second input of the subtraction unit 7 is the second information input Y ₂ (nΔω) of the unit 4 and is intended for connection with the output of the spectrum analyzer 3, the output of the subtraction block 7 is connected to the first input of the adder 8, the second input of which is the input of the offset code Y ₀ , the output of the adder 8 is connected to the combined information inputs of the DI registers of group 11, the outputs of which make up the N-channel output of block 4 comparison and connected to the corresponding N inputs (single information input) of the control unit 5, the clock inputs C of the registers of group 11 are connected to the corresponding N outputs of the decoder 10, the input of which is connected to the discharge output Q of the counter 9, the transfer output P of which is connected to the first input of the element 12 OR, the second input of which is the input RST of zeroing (initial setting) of the comparison unit 4, whose sync input CLK is the clock input of the counter 9. The control unit 5 is a line 13 of converters 13-1 ÷ 13-N of a digital code corrector control signals 1.

Many real distortion devices are active and amplify the input signal. And often during operation, the gain changes. For these reasons, to correctly compare the spectra, they should be normalized. By normalized spectra we mean the relative values Y ₁ (ω) and Y ₂ (ω) calculated in the spectrum analyzers 2 and 3, expressed by the formulas

,

,

where S ₁ (ω) and S ₂ (ω) are the spectra of the initial and resulting signals, respectively;

ω ₀ is a fixed average frequency within the operating frequency band (in sound technology, ω _{0 is} usually chosen to correspond to a frequency of 1 kHz).

The principle of operation of the automatic device shown in figure 1, is to compare the normalized spectrum Y ₁ (ω) of the original signal with the normalized spectrum Y ₂ (ω) of the resulting signal received at the output of the distorting path 6, and then in the compensating change in the frequency response of the circuits before the distorting path, so that the result of the comparison of the spectra satisfies some selected condition, for example, the minimum deviation of functions (the difference of the spectral components). To change the frequency response, use the frequency corrector 1, controlled by the comparison signals received at the output of block 4. The compensating change in the frequency response leads to a change in the ratios between the spectral components of the signal supplied to the input of the distorting path 6. Moreover, depending on the nature of the introduced distortions, leading to deformation of the spectrum of the signal, in the frequency corrector 1, both amplification and attenuation of individual spectral components can occur. In the example of FIG. 2, two amplification regions of the original signal and an attenuation region are shown.

The considered device (Fig. 1) implements the method according to the second embodiment (claim 7 of the claims). A device that implements the method according to the first embodiment differs from the one indicated only in that the analyzers 2 and 3 of the spectra are not standardized. If we are talking about a distorting path in which the signal is not amplified or attenuated, then there is no need to normalize the spectra. The same is done if the gain of the distorting path is known and constant. In this case, the output (resulting) signal is scaled taking into account the known value of the gain.

The distorting tract can have a different nature: to be purely electronic, mechanical or combined. The latter case in the practice of sound amplification is quite common, since a considerable part of the distortions is made by the propagation medium of sound waves and the electromechanical converters themselves. In such situations, to correct distortion at the input of the spectrum analyzer 3, the signal is fed through a measuring microphone installed at the point of reception of sound waves, similar to what is done in the well-known audio path tuning schemes.

Comparison block 4, as its name implies, has the functions of comparing spectra and generating signals that carry information about the results of the comparison. In special cases, a comparison can be made by calculating the difference between the values of Y ₁ (ω) and Y ₂ (ω) or their ratio. As for the control unit 5, its task is to convert the output signals of the comparison unit 4 directly into the control signals of the frequency corrector 1. The number of bands n of the frequency corrector 1, the adjustment range and the operating frequency band are selected based on specific tasks and quality requirements for automatic device. If we assume that corrector 1 is a purely analog device and control in each frequency band is carried out by voltage, the value of which determines the gain of the corrector in this band, then to connect the frequency corrector 1 with a digital comparison unit (which may be block 4), you only need a ruler digital-to-analog converters (DACs). This option is shown in figure 3, where as the converters 13-1 ÷ 13-N applied low-speed DACs.

The structure of the comparison unit 4 in FIG. 3 is proposed under the assumption that the spectrum analyzers 2, 3 are digital devices, the outputs of which have a sequence of samples — normalized values of the harmonics amplitudes Y ₁ (nΔω) and Y ₂ (nΔω), calculated, for example, by the discrete Fourier transforms provided that n = 1, 2, ... N (N is the total number of harmonics), and Δω is the step of arrangement of the samples along the frequency axis.

We assume that the samples Y ₁ (nΔω) and Y ₂ (nΔω) appear simultaneously in two channels and are accompanied by CLK clock pulses and, in addition, the change of samples in each channel also occurs with a clock frequency CLK. In the subtraction block 7, the difference Y ₁ (nΔω) -Y ₂ (nΔω) is calculated, after which the constant Y _{0 is} added to the adder 8 and then N obtained values

ΔY (nΔω) = Y ₁ (nΔω) -Y ₂ (nΔω) + Y ₀

are distributed across the N registers of group 11. The binary codes of N values ΔY (nΔω) entered in the registers 11-1 ÷ 11-N are the corrective control codes of the frequency corrector 1 and are sent to the DACs 13-1 ÷ 13-N.

The node consisting of the address counter 9 and the decoder 10 is controlled by writing the ΔY (nΔω) codes in registers 11 and the counter recounting module 11 selects one more than the number of samples N. This allows you to use the zeroed state of the counter as the initial and prohibit writing data to registers 11 With the advent of the first CLK clock pulse, counter 9 sets the unit code at the output Q and thus activates the output of decoder 10 with serial number “1” (the numbering of outputs of decoder 10 starts from zero; zero output is not used uetsya). Since this process proceeds stepwise, the positive voltage drop at the output "1" of the decoder 10, transmitted to the dynamic clock input of register 11-1, allows recording information about the first sample ΔY (Δω) in register 11-1. Then, with the arrival of the second clock, the counter goes into the next state corresponding to the number "2", and the process proceeds in a similar way. After the last count is written to register 11-N, counter 9 will be reset to zero, and the cycle of the first data recording will end there. All subsequent cycles are similar to the first and serve to update information in the registers 11. The RST input is intended for the initial reset of the comparison block. The offset code Y _{0 is} required to set the required constant offset voltage that controls the frequency corrector 1. Its value is selected based on the range of changes of ΔY (nΔω), the range of required adjustments and the control circuit parameters of corrector 1. The value of the code Y ₀ should be such that when Y ₁ (nΔω) -Y ₂ (nΔω) = 0, the bias voltage supplied to each of the control inputs of the corrector 1 would correspond to the transmission mode of the signal without changing its amplitude.

The application of the proposed methods and devices will make it possible to exclude not only a separate stage of preliminary testing of the working path, but also to obtain such an important new property of the correcting links as continuous tracking of distortions and their compensation within the capabilities of a particular equipment. The task of constantly monitoring distortions is relevant for changing parameters of the working path. We also add that automatic correction does not exclude manual, subjective, user-entered correction. Perhaps a combination of approaches. In addition, in automatic mode, you can enter corrective actions not continuously, but as necessary, for example, at certain time intervals, and by adjusting the depth of correction.

Regarding the features of the implementation of the methods, we note that the devices shown in the present description are not the only ones possible. To determine the spectra, you can use just one spectrum analyzer with storing the results. This is possible if the original signal is a stationary random process or periodic deterministic. Of course, in these cases, the duration of the signal analysis should be selected sufficient to obtain a low-independent or time-independent estimate.

Claims (11)

1. The method of frequency correction, characterized in that they determine the normalized spectrum of the original signal, determine the normalized spectrum of the resulting signal subjected to frequency distortion, compare the normalized spectra of the original and the resulting signals, the comparison results are used to influence the original signal to change the ratios between its spectral components. 2. The method according to claim 1, characterized in that the normalized spectra of the source and resulting signals are compared by calculating the difference of the spectral components corresponding to n points of the spectrum, where n is an integer, a finite number. 3. The method according to claim 1, characterized in that the normalized spectra of the source and resulting signals are compared with each other by calculating the ratio of the spectral components corresponding to n points of the spectrum, where n is an integer, a finite number. 4. The method according to claim 1, characterized in that the normalized spectra of the source and resulting signals are spectra of average values. 5. The method according to claim 1, characterized in that the normalized spectra of the source and resulting signals are energy spectra. 6. The method according to claim 1, characterized in that the normalized spectra of the source and resulting signals are spectra obtained by the method of discrete Fourier transform. 7. The automatic device that implements the method according to claim 1, containing a controlled frequency corrector, the input and output of which respectively serve as the input and output of the device, characterized in that the analyzer of the normalized spectrum of the source signal, the analyzer of the normalized spectrum of the resulting signal, a comparison unit and the control unit, the comparison unit is used to compare the normalized spectra of the source and the resulting signals obtained using spectrum analyzers, the control unit serves to directly control of the frequency corrector by comparing the normalized spectra of the source and resulting signals. 8. The automatic device according to claim 7, characterized in that the signal at the input of the spectrum analyzer of the resulting signal is fed directly from the output of the electronic part of the distorting path. 9. The automatic device according to claim 7, characterized in that the signal at the input of the spectrum analyzer of the resulting signal with a distorting acoustic path is supplied from a measuring microphone installed in the receiving area of the acoustic waves. 10. The automatic device according to claim 7, characterized in that the controlled frequency corrector is a multiband graphic equalizer with electronic control. 11. The comparison unit for use in the automatic device according to claim 7, comprising a subtraction unit, an adder, an address counter, an address decoder, a group of registers and an OR element, the first input of the subtraction unit is an information input of the control unit, the reference input of which is the second input of the subtraction unit whose output is connected to the first input of the adder, the second input of which is the input of the offset code, the output of the adder is connected to the combined information inputs of the group registers, the clock inputs of the group registers are connected s to the corresponding outputs of the decoder, whose input is connected to the discharge outlet counter carry output coupled to a first input of the OR gate, the second input of which is the reset input of the comparator, a clock input of the counter is a clock terminal of the comparator, the output of which are the output of register group.

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