JPS5923159B2 - A method for removing interference distortion caused in the demodulated signal due to interference of FM wave signals in the recording and playback system of multi-channel disc records. - Google Patents

Description

[Detailed Description of the Invention] Crosstalk between a plurality of transmission paths through which angle modulated wave signals (hereinafter referred to as FM wave signals in this specification) such as FM wave signals and PM wave signals are transmitted. It is well known that when this occurs, interference distortion occurs in the demodulated signal obtained by demodulating each FM wave signal of each transmission path due to interference between the FM wave signals due to the presence of crosstalk. .

Conventionally, demodulation is performed to remove interference distortion that occurs in the demodulated signal due to crosstalk that exists between multiple transmission paths on which FM wave signals are transmitted.) The previous state of the FM wave signal In some cases, a so-called crosstalk canceling circuit is sometimes used to add a canceling signal having the same amplitude and opposite phase to another FM wave signal that is crosstalking to the FM wave signal. However, in this conventional crosstalk cancellation circuit, the FM wave signals being transmitted on each transmission path interfere with the FM wave signals being transmitted on each other's transmission path due to the crosstalk that exists between the transmission paths. It has been extremely difficult to construct a device that can perform a good cancellation operation when the amount of crosstalk or amount of phase shift changes over time.

By the way, for example, in the so-called CD-4 four-channel stereophonic recording and reproducing system, a sum signal of two channel signals constituting a pair of front and rear channels and a difference signal between the two channel signals are used as signal waves (modulated). A signal or a modulated wave) is frequency-multiplexed with an FM wave signal obtained by angle modulating (FM and PM) a carrier wave with an appropriate frequency value to form a set of multiplexed signals, and is configured as described above. Multiple sets of multiplexed signals are recorded as one on a disc record.
In a multi-channel stereophonic recording and playback system using a disc record that records sound into the sound grooves of a book and plays it back, the transmission system of the recording system (recording system) and playback system is Since elements (cutters, pick-ups) whose crosstalk and phase shift amount vary over time are used, interference between FM waves in the recording and playback system of multi-channel disc records causes problems in the demodulated signal. It is extremely difficult to effectively eliminate the interference distortion that occurs even using the conventional crosstalk cancel circuit described above.
Pick-ups used in playback systems are limited by price, and there is a limit to how well they can improve the crosstalk characteristics between the left and right channels. The occurrence of interference distortion was unavoidable.

The present invention improves interference distortion caused in a demodulated signal due to interference between FM wave signals in the recording and playback system of a multi-channel disc record by performing necessary signal processing on the demodulated signal. The present invention provides a method for removing interference distortion, the contents of which will be specifically explained below with reference to the accompanying drawings.

The attached drawing is a block diagram of the interference distortion removal method of the present invention. In this figure, 1 indicates the L channel FM wave signal Cl (
t) input terminal, 2 is the R channel FM wave signal Cr(
t) is an input terminal.

The FM wave signals C1(t) and Cr(t) of the respective channels supplied to the input terminals 1 and 2 are shown in (3) below. FM of other channels as shown in equation (4)
A state where there is no wave signal interference, that is, the following (1
). The original L channel FM wave signal CL(t) and the original R channel FM wave signal shown in equation (2), respectively.
The wave signal CR(t) is in a state where the FM wave signal of the other channel is crosstalking with each other at a crosstalk ratio K. When the L channel FM wave signal No. 5 Cl(t) shown by the above equation (3) is demodulated by the first demodulator 3, the following (5) is output from the first demodulator 3.
The demodulated signal Dl(t) as shown by the equation is output, and the R channel FM wave signal Cr(t) shown by the above equation (4) is demodulated by the second demodulator 4. and,
The second demodulator 4 outputs a demodulated signal Dr(t) as shown by the following equation (6).

{However, θ(t) = f(t) - g(t), which is the same in each formula described below} Demodulation output from the first demodulator 3 and the second demodulator 4, respectively When the signal does not contain interference distortion, the demodulated signal is sent to the first demodulator 3.
Since fτt) for the second demodulator 4 and g/(t) for the second demodulator 4, the first and second demodulators shown in equations (5) and (6) above, respectively It can be seen that the demodulated signals Dl(t) and Dr(t) from No. 3 and No. 4 contain a large amount of distortion components.

Now, in general, when FM wave signals interfere with each other due to crosstalk, the interfered FM wave signals cause phase changes and amplitude fluctuations, and the envelope of the amplitude fluctuations of the FM wave signals that occurs at this time is Env. (t) is expressed by the following equation (7).

By the way, the above-mentioned (5
), (6) and the above ((6), which represents the envelope of amplitude fluctuations that occur in an FM wave signal that has been interfered with by other FM wave signals.
Comparing Equation 7), the denominators of each of Equations (5) and (6) above are E shown in Equation (7) above.
nv(t) squared, and therefore the envelope of the amplitude fluctuation of the FM wave signal and its FM
There is a correlation between the distortion components in the demodulated signal of the FM wave signal, and using this relationship, it is possible to cancel the distortion component in the demodulated signal of the FM wave signal using the envelope of the amplitude fluctuation of the FM wave signal. is possible.

In the figure, components indicated by blocks 5 to 9 are components configured to cancel interference distortion in the demodulated signal based on the above considerations, and 5 is a first analog multiplier. , whose X input terminal is given the demodulated signal Dl(t) from the first demodulator 3, and 6 is a second analog multiplier, whose X input terminal is given the demodulated signal Dl(t) from the first demodulator 3. A demodulated signal Dr(t) from the demodulator 4 is given.

The Y input terminals of the first and second analog multipliers 5 and 6 receive an envelope signal Env(t) generated by an envelope signal generation circuit S made up of blocks 7 to 9, which will be described later. given, the output signal Dl(t)・Env(t) from the first analog multiplier 5
is supplied to the first arithmetic unit 12 and the second arithmetic unit 14,
Furthermore, the output signal Dr(t
)·ErIv(t) is supplied to the first arithmetic unit 12 and the third arithmetic unit 15.

The envelope signal generation circuit S detects the envelope Env(t) of the amplitude fluctuation of the input signal using a square characteristic when an FM wave signal that has been interfered with by an FM wave signal of another channel is given as an input signal. It has a function of outputting it as an envelope signal Env(t), and in the illustrated example, it is assumed that the R channel FM wave signal Cr(a) is given as an input signal. However, as an input signal L
An FM wave signal Cl(t) of the channel may be provided. In the envelope signal generation circuit S, 7 is an automatic gain control circuit (hereinafter referred to as AGC circuit 7), and this A
The GC circuit 7 performs an automatic gain control operation on the FM wave signal applied as an input so as not to cause amplitude fluctuations in the output signal from the AGC circuit 7 at a frequency lower than the lower limit frequency of the audible frequency band. , whereby, for example,
Even if pickups with different output sensitivities are used to reproduce signals from disc records,
In order to effectively remove interference distortion, it is possible to prevent changes in the signal level of the demodulated signal sent to the output terminal (the significance of the existence of this AGC circuit 7 will be explained later). described again). The output signal from the AGC circuit 7 described above is
The analog multiplier 8 outputs a signal obtained by squaring the output signal of the AGC circuit 7.

The output signal of the analog multiplier 8 is applied to a reduction filter 9, where the carrier component is removed, so that the output signal from the envelope signal generation circuit S is the amplitude fluctuation of the FM wave signal given as the input signal. The signal content {Env(t)}2 whose envelope Env(t) is squared
An envelope signal Env(t) as expressed by the following equation (8) is obtained. Env. (t)={En
v(t)}2=1+K2+2Kc0sθ(t)...
・・・・・・・・・・・・(8) Therefore, this (8)
The envelope signal Env(t) as shown in the equation is applied to each Y input terminal. The respective output signals Dl(
t)・Env(t), [Dr(t)・Env(t
) are respectively expressed by the following equation (9), aω.

The output signals of the first and second analog multipliers 5 and 6 described above are added in the first arithmetic unit 12, so that
The signal expressed by the following aυ equation is applied to the Y input terminal of the third multiplier 11, and the output signal of the first analog multiplier 5 is output to the second arithmetic unit 14. The output signal of the second multiplier 6 is added to the minuend input terminal as a minuend signal, and furthermore, the output signal of the second multiplier 6 is applied to the minuend input terminal of the third arithmetic unit 15 as a minuend signal.

{Here, the crosstalk ratio K is smaller than 1, and the crosstalk ratio K in a normal pick-up cartridge is smaller than 0.1, so the second term in the above aυ formula can be omitted. , Therefore, the above equation aυ can be expressed as the following equation (ΠA)} The X input terminal of the third multiplier 11 receives the envelope signal generated by the envelope signal generating circuit s described above. Env(t)
The signal obtained through the coupling capacitor 10, that is, the AC component of the envelope signal Env(t) 2Kc0sθ(t
) is supplied to it, and its Y input terminal is supplied with the output signal of the first arithmetic unit 12, that is, the signal shown by the above equation (IIA), as described above. Therefore, on the output side of the third multiplier 11, a signal as shown in the following equation is output.

The output signal from the third multiplier 11 as shown in the above equation A2) is adjusted to a signal level ι1 -! by the resistive attenuator 13 so that the signal level becomes ι1 -! -V2) When the adjustment is performed, a distortion component canceling control signal Ec(t) as shown in the following test a is obtained.

The distortion component cancellation control signal Ec(t
) is given as a subtraction signal to the second and third arithmetic units 14 and 15, respectively, and one of the second
The arithmetic unit 14 performs the calculation of {Equation (9)}-{A, Equation}, and outputs {Flt)+ to the output terminal 16.
K2gτt)} An output signal shown as {A
, formula} is performed, and the output terminal IT becomes {
g'(t)+K2r(t)} An output signal is sent out. As mentioned above, the output signals sent to each output terminal 16 and IT individually are {fτt)+
K2glt)}, {Glt)+K2fτt,
The signal does not contain any interference distortion, and by applying the interference distortion removal method of the present invention, the first demodulator 3 and the second demodulator 4
It can be seen that the interference distortion is successfully removed from the demodulated signal, that is, the signal containing the interference distortion as shown in equations (5) and (6).

Note that K in the output signal sent to the output terminal 16
The signal component 2g'(t) and the signal component K2f'(t) in the output signal sent to the output terminal IT are the original output signal g'' of the other channel, respectively.
(t), fτt), which is not originally an interference distortion, and as mentioned above, the magnitude of the other channel signal component appearing in the output signal is generally a crosstalk signal component with a value smaller than 1. This is a value obtained by multiplying the original output signal of the other channel by a value K2, which is the value of the talk ratio K squared, and is usually a small value that can be ignored. Next, a supplementary explanation will be given regarding the AGC circuit 7 used in the envelope signal generation circuit S described above. As mentioned above, the output sensitivity of pickup cartridges used to reproduce signals from disc records often differs from cartridge to cartridge. When reproducing signals from the FM wave signal, the signal level of the FM wave signal will differ depending on the output sensitivity of each cartridge, and naturally the magnitude of the amplitude fluctuation of the FM wave signal will also vary depending on the output sensitivity of the FM wave signal. The result will be different depending on the difference in the signal level. So, A
When the signal level of the FM wave signal changes as described above when the GC circuit 7 is not used, the signal level of the FM wave signal changes based on the detected value of the square characteristic of the envelope of the amplitude fluctuation of the FM wave signal performed by the envelope signal generation circuit S. The envelope signal generated by the demodulated signal changes greatly, which not only makes it difficult to remove interference distortion in the demodulated signal, but also causes the signal level of the output signals obtained at the output terminals 16 and 17 to fluctuate widely. This will cause inconvenience.

For example, when the output sensitivity of a pickup cartridge used for signal reproduction from a disc record is G, the L channel FM wave signal C1(t) is expressed by the following (self) equation, and D1( t)・E. ．． ,,(
t)-E,. (t)=G2[f'(t)+K2g'(t
)+K (as shown, therefore, the output signal from the second arithmetic circuit 14 is 1-G2){f'(t)+
g′(t)}COsθ(t)] ・・・・・・・・・・・・
...An, there is no problem in terms of price, and therefore, the method of the present invention can be successfully applied to consumer equipment without any problem in terms of price. For example,
When the system of the present invention is applied to a CD-4 system playback device, even if the pickup cartridge used for signal playback from a disc record has somewhat poor separation characteristics, interference in the demodulated signal will occur. It has the advantage that it can be removed well and demodulation can always be performed with high fidelity.

[Brief explanation of drawings]

The accompanying drawings are block diagrams of one embodiment of the method of the present invention. 1, 2... Input terminal, 3, 4... Demodulator, 5, 6, 8, 11... Analog multiplier, 7
...AGC circuit, 9...Low pass filter,
10... Coupling capacitor, 12, 14, 15.
... Arithmetic unit, 13 ... Resistance attenuator, 16
, 17... Output terminal.

Claims (1)

[Claims] 1 A first demodulated signal Dl( having interference distortion obtained by demodulating an L-channel FM wave signal Cl(t) containing a crosstalk component of an R-channel FM wave signal by a first FM demodulator)
t) to the X input terminal of the first analog multiplier, and an R channel FM wave signal Cr(t) containing a crosstalk component of the L channel FM wave signal by a second FM demodulator. The second demodulated signal Dr(
t) to the X input terminal of the second analog multiplier;
An envelope signal e_n in which the envelope of the FM wave signal of one of the channels is detected with a square characteristic.
Means for obtaining _v(t) and said envelope signal e_
means for applying n_v(t) to the respective Y input terminals of the first and second analog multipliers, and means for applying the alternating current portion of the envelope signal e_n_v(t) to the X input terminal of the third analog multiplier; means for providing, and the above-mentioned first and second
means for applying a signal obtained by adding the output signals from the multipliers by the first arithmetic unit to the Y input terminal of the third analog multiplier; a control signal e_c(t) for canceling distortion components by adjusting the output signal of means for applying the output signal of the first analog multiplier as a minuend signal to the arithmetic unit; and means for applying the output signal of the second analog multiplier as the minuend signal to the third arithmetic unit; Due to the interference between FM signals in the recording and playback system of a multi-channel disc record, in which the desired demodulated signals from which interference distortion has been removed are obtained at the output sides of the second and third arithmetic units, respectively. A method for removing interference distortion that occurs in demodulated signals.