JPS5934039B2 - Multi-channel record demodulation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for modulating an angle modulated wave signal when demodulating an angle modulated wave signal reproduced from a multi-channel record in which a direct wave signal and an angle modulated wave signal are multiplexed and recorded. A phase-locked loop (hereinafter abbreviated as PLL), which has a relatively wide locking range in the middle and low frequencies of the signal, demodulates a modulated signal with a large frequency deviation with less abnormal sound (including distortion) and has a relatively wide locking range. A PLL with a narrow lock range demodulates the direct wave signal band to the angle modulated wave signal band so that the influence of interference waves is small, and the demodulated outputs of multiple PLLs are switched and added to generate a single signal. In the switching circuit of the demodulator that obtains the demodulated output, we propose a multi-channel record demodulation method that performs switching addition so that a constant level of demodulated output is always obtained regardless of the operation of the switching circuit, and obtains a demodulated output that eliminates abnormal sounds. It is something to do.

If a PLL is used to demodulate an angle modulated wave signal played from a multi-channel record in which a direct wave signal and an angle modulated wave signal are multiplexed and recorded, interference will occur from the direct wave signal band to the angle modulated wave band. When waves occur or when the frequency deviation of the modulated signal, which has a lot of energy distributed in the middle and low frequencies, is larger than the lock range of the PLL, the PL
L deviates from the locked state and generates a harsh abnormal sound in the reproduced sound.

In order to reduce the above-mentioned abnormal noise, the present applicant has proposed a demodulation method using a plurality of PLLs, an embodiment of which is shown in FIG.

For the sake of simplicity, the previously proposed demodulation method will be described below using an example in which two PLLs are used. That is, the angle-modulated wave signal input from the input terminal 1 is applied to the PLL 2 having a wide lock range and the PLL 4 having a narrow lock range compared to the lock range of the PLL 2.

The demodulated output is provided by a delay circuit 3 and a high frequency correction circuit 5, respectively.
The delay time difference due to the difference in lock range and the high frequency characteristics are corrected and applied to the adder 6, and the demodulated signal of the reproduced angle-modulated wave signal is taken out from the output terminal 7. According to such a configuration, the signal-to-noise ratio is improved by 6 dB compared to demodulation using one of the PLLs. When abnormal noise occurs in both PLLs, since the abnormal noises generated in both PLLs are caused by different causes, the sources can be considered to be completely independent from each other, so the demodulated signal is determined by adding the in-phase signals. Therefore, for the abnormal sound, different signals are added, and if these levels are equal, the level after addition is 2 for the demodulated signal.
Double, as for the abnormal sounds! Therefore, the signal-to-noise ratio is improved by 3 dB compared to when each is used alone. As a practical matter, this level of improvement cannot reduce abnormal noise to the point where it cannot be detected by the ears, and if multiple PLLs are used, the abnormal noise can be improved depending on the number of PLLs, but In practical terms, the number of such devices is naturally limited. The present invention is intended to eliminate the above-mentioned drawbacks, and will be described with reference to one embodiment shown in FIG.

For the sake of simplicity, the following explanation will be based on the case where two PLLs are used. That is, the angle-modulated wave signal input from the input terminal 8 is applied to the two PLLs 9 and 1O.

The PLL 9 has a locking range that is equal to or wider than the maximum deviation frequency range of the modulation signal of the angle-modulated wave signal, and is suitable for modulation signals with a lot of energy distributed in the middle and low frequencies, such as trumpet sounds. On the other hand, demodulation with less distortion is performed, but it is not possible to prevent abnormal sounds caused by interference waves from the direct wave signal band to the angle-modulated wave signal band.
The demodulated output of the PLL 9 is applied to the delay circuit 11, and the PLL
9. Compensate for the delay time difference caused by the difference in the lock range of 1O. PLL1O has a narrower lock range than PLL9, and for example, for modulated signals such as cymbal sounds where a lot of energy is distributed especially in high frequencies, the narrow lock range causes high frequencies and slow tracking. This reduces the apparent distortion and at the same time reduces the generation of abnormal sounds caused by interference waves from the direct wave signal band to the angle modulated wave band. However, when demodulating an angle-modulated wave signal having a large frequency shift, an abnormal sound is generated. The demodulated output of PLLIO is sent to the high frequency correction circuit 12.
is applied to correct the attenuation of the high frequency demodulated signal. The outputs of the delay circuit 11 and the high frequency correction circuit 12 are applied to a switching adder circuit 13, and a demodulated signal of the reproduced angle-modulated wave signal is taken out from an output terminal 14. The switching elements 15 and 16 of the switching circuit 13 are PLLs 9 and 1O.
A synchronous detector, etc. that detects the PLL's loss of lock by detecting the phase error between the oscillation output of the voltage controlled oscillator in the PLL connected to the PLL and the angle-modulated wave to be demodulated, and generates an abnormal sound detection signal. They are each controlled by an abnormal sound detection signal from the abnormal sound detection means. When an abnormal sound caused by interference waves from the direct wave signal band to the angle-modulated wave signal band occurs in the demodulated output of the PLL 9, the switching element 15 is immediately set to 0FF by the abnormal sound detection signal of the PLL 9. That is, the demodulated signal of PLL 9 is cut off. At this time, the PLLIO has a narrow lock range, a small loop gain, and a slow high frequency follow-up performance. Therefore, the interference wave disappears before the output of the voltage controlled oscillator locks to the interference wave. In other words, during the demodulation output of the PLLIO, The probability that abnormal sounds will occur is very low. Therefore, only the demodulated output of PLLIO is taken out from the output terminal 14. At this time, with a combination of a simple switching circuit and an adder circuit, the output level taken out from the output terminal 14 is 6 dB compared to the output level when both demodulated outputs of PLL 9 and IO are used.
Attenuation occurs. This causes a significant change in the separation of the matrixed final reproduced sound when playing a multi-channel record, which is undesirable. Therefore, the present invention uses a switching adder circuit whose output level is always constant regardless of the switching operation. The switching adder circuit 13 will be described in detail later. When an abnormal sound is generated in the demodulated output of the PLLIO due to a modulation signal having a frequency deviation larger than the lock range in which more energy is distributed in the middle and low frequencies, the switching element 16 is activated by the abnormal sound detection signal of the PLLIO. It becomes 0FF immediately. That is, PLLlO
The demodulated signal is obliquely cut. At this time, since the PLL 9 has a lock range that is equal to or wide than the maximum deviation frequency range of the modulation signal of the angle-modulated wave signal, no abnormal sound is generated in its demodulated output. Therefore, only the demodulated output of PLL 9 is taken out from output terminal 14 at the same level as when both demodulated signals of PLL 9 and IO are applied. In FIG. 2, the delay circuit 11 and the high frequency correction circuit 12 are connected to the PL
If the disturbance in the frequency characteristics of the demodulated signal at the output terminal 14 due to the delay time difference between L9 and 1O and the difference in high frequency characteristics is within a permissible value, it may be omitted.

Further, when two or more PLLs are used, a similar circuit configuration can be made, and depending on the number of PLLs, it is possible to respond to abnormal sounds more precisely. In addition, 17 in the figure is the switching element 15.
, 16 outputs.

FIG. 3 shows an embodiment using transistors of the switching adder circuit 13 used in the present invention.

The following explanation uses two transistors for simplicity.
Do this for signals. That is, input terminal 18,1
The input signal applied to the transistor 9 is switched and added by the transistors 20 and 21, and then taken out from the output terminal 22.

The switching operation is performed by applying control voltages from the detection circuits to the bases of the transistors 20 and 21 according to respective signals. Transistor 20 below
, 21 are both 0N, and the fact that the level at the output terminal 22 when either one is 0FF will be quantitatively explained. The input voltages applied to the input terminals 18 and 19 are Eil and ei2, the signal source impedances are Rgl and Rg2, the resistance values between the emitters and collectors of the transistors 20 and 21 are Rl and R2, and the resistor 23
Let the resistance value of R9 be R9.

The values of Rl and R2 change depending on 0N and 0FF. If the output voltage at the output terminal 22 is EO, then.

Here, the signals applied to input terminals 18 and 19 are
Since it is a corrected version of the LL demodulated signal, it can be considered that they are almost the same.

From equations (1) and (2).

If both transistors 20 and 21 are 0N, transistors with the same characteristics can be used.

From equations (3) and (4).

Here, if R-+o and R3>JG.

Transistor 20 is 0N and transistor 21 is 0N.
In the case of an FF, Equation (3) holds, and this is because R1→0, R2→1, and from Equations (7) and (8).

Here, if R3>Rg.

The same applies when the transistor 20 is OFF and the transistor 21 is ON.

Therefore, the output level when both transistors 23 and 24 are 0N and the output level when one of transistors 20 and 21 is 0FF is that R3 is sufficiently larger than Rg, that is, the previous stage of the transistor is low. If the output impedance of the next stage is high input impedance, they are equal.

In Fig. 3, the switching elements are transistors, FE
Any type of element may be used as long as the switching operation is performed by a control signal such as T. Further, even when there are two or more input signals or a plurality of input signals, a similar circuit configuration can be made, and the output level will always be constant. The present invention uses a PLL having a wide lock range and a PLL having a relatively narrow lock range when demodulating an angle modulated wave signal reproduced from a multi-channel record in which a direct wave signal and an angle modulated wave signal are multiplexed and recorded. Since multiple units are used and their demodulated outputs are added by switching to obtain a demodulated signal of the angle-modulated wave signal at a constant level regardless of the switching operation, there is a lot of energy in the middle and low frequencies of the angle-modulated signal. Eliminates abnormal sounds that occur during demodulation output due to apparent overmodulation phenomena caused by distributed modulation signals and interference from the direct wave signal band to the angle-modulated wave signal band without changing the demodulation signal level. Therefore, when a multi-channel record is played by a player using the present invention, separation between channels in the playback sound field is maintained in a good state.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the multi-channel demodulation method previously proposed by the applicant, FIG. 2 is a block diagram of an embodiment of the demodulation method according to the present invention, and FIG. 3 is a block diagram of an embodiment of the demodulation method according to the present invention. FIG. 2 is a diagram illustrating a switching adder circuit that can be used for 8, 18, 19... Input terminal, 9...
PLL having a wide lock range, 10... PLLlll having a narrow lock range... Delay circuit, 12... High frequency correction circuit, 13...
・Switching adder circuit, 14, 22... Output terminal, 15, 16... Switching element, 17
... Addition circuit, 20, 21 ... Transistor, 23 ... Resistor.

Claims (1)

[Claims] 1. When demodulating the angle-modulated wave signal played from a multi-channel record in which a direct wave signal and an angle-modulated wave signal are multiplexed and recorded, a phase-locked loop with a relatively wide lock range characteristic is used. These phase locked loops each have at least one phase locked loop with narrow locking range characteristics.
The angle modulated wave signal to be demodulated is added to the loop to perform demodulation, and a plurality of demodulated outputs are obtained from these phase-locked loops. These plurality of switching elements are turned on and off in response to the abnormal sound, so that the impedance when turned off becomes substantially infinite,
A multi-channel record demodulation method characterized in that a demodulated signal of the angle-modulated wave signal with abnormal sounds removed and always at a constant level is obtained by adding these plurality of demodulated outputs.