JPS5952598B2 - 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. In the middle and low frequencies of the signal, a phase-locked loop (hereinafter abbreviated as RLL) with a relatively wide lock range demodulates a modulated wave with a large frequency shift with little distortion.
In addition, at the high frequency of the modulated signal, the PLL with a relatively narrow lock range demodulates the signal so that the influence of interference waves from the direct wave signal band to the angle-modulated wave signal band is small.
It is an object of the present invention to provide a multi-channel record demodulation method that reduces distortion occurring in the demodulated output by adding the demodulated outputs of the LL, and also obtains a demodulated signal with an improved signal-to-noise ratio.

FIG. 1 shows a block system diagram of an example of a PLL.

Generally, when reproducing a multi-channel record, one PLL is used to demodulate the angle modulated wave signal. That is, in FIG. 1, the reproduced angle-modulated wave signal inputted from the input terminal 1 is supplied to the phase comparator 2, where a voltage-controlled oscillator (hereinafter referred to as VCO) whose center frequency is the carrier frequency of the angle-modulated wave signal is supplied. After being phase-compared with the signal from (omitted) 5 and made into an error voltage according to their phase difference, it is supplied to the loop filter 3, where its high frequency components are attenuated. The signal taken out from the loop filter 3 is amplified by the DC amplifier 4 and then supplied to the VCO 5 as a control voltage to control its output oscillation frequency, while being taken out from the output terminal 6 as a demodulated signal of the angle modulated wave signal. It will be done.

In this way, the PLL can be regarded as a type of filter, and has the characteristic of passing signals in a certain frequency range.

This is the capture range or lock range characteristic, and its passband (lock range) is determined according to the level of the input angle-modulated wave, and the range can also be varied artificially. Therefore, the frequency characteristics of the demodulated signal are determined by the lock range of the PLL. By the way, when playing a multi-channel record, an abnormal drop in the carrier of the reproduced angle modulated wave signal,
Alternatively, abnormal noise may occur in the reproduced sound of the multi-channel record due to overmodulation caused by interference waves close to the carrier due to harmonics of the direct wave signal.

Therefore, in order to reduce and eliminate the above noise, conventional PLL
By making the lock range approximately equal to the maximum deviation frequency of the modulation signal, or narrower than it when an abnormal phenomenon occurs, abnormal lock is prevented, and at the same time, the high frequency (around 8 KHz) of the demodulation signal is attenuated to reduce the apparent noise. lowering the level.

As is well known, the capture range or lock range of this PLL is determined by the loop gain of the PLL, and the main factors of this loop gain are the gain of the DC amplifier 4, the amount of passage through the loop filter 3, and the conversion gains of the phase comparator 2 and VCO 5. to do. As a method of varying the lock range by increasing or decreasing the loop gain of this PLL, the main method is to increase or decrease the loop gain of the PLL. A method is usually used to obtain a desired lock range by changing the characteristics of the router and controlling its output signal. The second shows a specific circuit of an example of a conventional loop filter.

In the figure, 7 is on the output side of the phase comparator 2. This input terminal is connected to an output terminal 8 which is connected to the input side of the DC amplifier 4 via a resistor R1. A connection point between the resistor R1 and the output terminal 8 is grounded via a series circuit consisting of a capacitor C1 and a variable resistor R2. As a result, the loop filter is formed from a low-pass filter, and by varying the variable resistor R2, a desired frequency characteristic as shown in FIG. 3 can be obtained. That is, the frequency characteristics of the lagged filter shown in FIG. 2, which is conventionally used as the loop filter 3, are as shown in FIG.
The frequency f1 is determined by the capacitance value of R1 and the resistance value of resistor R1.
and frequency F2 determined by the capacitance value of capacitor C1 and the resistance value of variable resistor R2.

It is attenuated at DB/0ct, and has flat characteristics at frequencies below f1 and above F2. The lock range characteristic of the PLL at this time is as shown by the solid line in FIG. Here, Fc in FIG. 4 indicates the carrier frequency of the input angle-modulated wave signal. Furthermore, when the resistance value of the variable resistor R2 is made small, the frequency characteristic of the loop filter 3 becomes as shown by the broken line in FIG. The characteristics are varied as shown by the broken line in FIG.

Similarly, when the resistance value of the variable resistor R2 is further reduced, the frequency characteristics of the loop filter 3 and the lock range characteristics of the PLL become as shown by the dashed lines in FIGS. 3 and 4, respectively. Normally, the frequency F2 shown in Fig. 3 is selected to be about 10Hz, and the output of the loop filter 3 increases or decreases uniformly at all frequencies, and as a result, the lock range has frequency characteristics. It can be said that it is not.

In other words, even if an angle-modulated wave signal whose carrier is modulated with a modulation signal of high frequency (around 8KHz) enters the PLL, the carrier wave (carrier) is modulated with a modulation signal of mid-low frequency (around 2KHz or less). Even if the angle-modulated wave signals modulated by the angle-modulated wave signals enter the PLL, these angle-modulated wave signals are always uniformly controlled.

Therefore, when playing a multi-channel record, an angle-modulated wave signal whose carrier is modulated with a modulation signal such as a cymbal sound in which a lot of energy is distributed particularly in high frequencies (around 8 KHz) enters the PLL. In this case, in order to prevent abnormal noise, the variable resistor R2 is varied so that its maximum deviation frequency is narrower than the lock range that is approximately equal to the deviation frequency of the modulated signal, thereby changing the angle-modulated wave signal from the direct wave signal band. The transient response of the PLL also decreases to the abnormal angle modulated wave that is formed separately from the original angle modulated wave signal caused by interference waves entering the band, so the abnormality to the above abnormal angle modulated wave is reduced. At the same time that lock is prevented, even if lock occurs, PLL
Due to the high-frequency attenuation characteristic of the demodulated signal due to the decrease in the loop gain, the apparent noise level is reduced and abnormal sounds are no longer perceptible to the auditory sense.

However, if the modulation signal has a lot of energy distributed especially in the middle and low frequencies (around 2KHz or less), such as a trumpet sound, and the deviation frequency of this modulation signal exceeds the rock range, the rota range An apparent overmodulation phenomenon occurs due to the narrowness of the angle, and abnormal noise as shown in FIG. 5B occurs in the demodulated signal of the PLL even though the angle-modulated wave is normal.

This abnormal noise is different from the case of the above-mentioned high frequency modulation signal shown in FIG. 5A, and can be audibly perceived as an extremely harsh sound. In other words, since the conventional PLL described above uniformly narrows the lock range, abnormal noise can be audibly ignored in the case of high-frequency modulation signals, but in the case of mid-low frequency modulation signals, the angle-modulated wave signal is normal. Despite this, there was a drawback that the lock was lost and a bead sound was generated between the output signal of the VCO 5 and the input signal of the PLL, which was audibly perceptible. On the other hand, if the lock range is widened, the PL
L continues to steadily hold the locked state.

In other words, the transient response becomes quick and slips (jumping one modulated wave signal and locking onto the next signal) do not occur, so even a slight abnormality in the angle modulated wave signal will cause abnormal noise. I can hear it. Therefore, the PLL in this case
does not cause a loss of lock due to the narrow lock range near the medium and low frequencies mentioned above, but conversely, when the modulation signal of the input angle modulated wave signal has a large energy distribution in the high frequency range, responds to even the slightest abnormality, interference waves jump from the direct wave signal band to the angle-modulated wave band, and the frequency characteristics of the demodulated signal do not have high-frequency attenuation characteristics, so abnormal noise The disadvantage was that the sound became aurally perceptible. The present invention eliminates the above-mentioned drawbacks, and one embodiment thereof will be described with reference to 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 9 is applied to the two PLLs 1O and 11, respectively.

PLLIO has a lock 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 where energy is particularly distributed in the middle and low frequencies, such as trumpet sounds. However, the occurrence of distortion caused by interference waves jumping from the direct wave signal band to the angle-modulated wave band cannot be prevented.

The demodulated output of PLL1O is applied to delay circuit 12. The delay circuit 12 compensates for the difference in delay time caused by the difference in lock range between the demodulated outputs of the PLLs 10 and 11. PLLll has a narrow rotary range compared to PLLlO, and for example, it attenuates the high-frequency demodulated signal for modulated signals where a lot of energy is distributed particularly in the high-frequency range, such as cymbal sounds, and reduces the apparent noise level. At the same time, the generation of distortion caused by interference from the direct wave signal band to the angle modulated wave signal band is reduced. However, when demodulating a modulated wave signal having a frequency deviation larger than the lock range in which much energy is distributed in the middle and low frequencies, distortion as shown in FIG. 5B occurs. The demodulated output of PLLll is applied to the high frequency correction circuit 13. The high frequency correction circuit 13 corrects the narrow lock range of PLLll and the attenuation of the high frequency demodulated signal. delay circuit 12,
The output of the high frequency correction circuit 13 is applied to an adder circuit 14, and a demodulated signal of the reproduced angle-modulated wave signal is taken out from an output terminal 15. When interference waves jump from the direct wave signal band to the modulated wave band, no distortion occurs in the demodulated output of PLL11, but distortion (noise) occurs in the demodulated output of PLL10. The demodulated signals by PLLlO and ll are corrected to be equal by the delay circuit 12 and the high frequency correction circuit 13, and if this is set as Vs and the noise component generated in the demodulated output of PLLlO is set as Qvnl2, then PLLlO and ll are corrected to be equal.
The demodulated output by O is Vs+Sy/2, and output terminal 1
5, ``'' becomes 2Vs+VVnl2, and the signal-to-noise ratio is improved by 6 dB compared to when PLLlO is used alone.

If the deviation frequency of the modulation signal, which has a lot of energy distributed in the middle and low frequencies, exceeds the lock range of the PLL10, no distortion will occur in the demodulated output of the PLL10, but the PLL1
Distortion (noise) occurs in the demodulated output of l.

If the noise component is s/2, output terminal 1
5, the result is 2VS+Q2, and the signal-to-noise ratio is improved by 6 dB compared to when PLLll is used alone. Furthermore, a case where the above two noises occur simultaneously will be described.

Demodulated output by PLL]0 goes to s+2 Demodulated output by PLL11 goes to Vs+! It is Vn22.

On the other hand, since the noise components are generated by different causes, they can be considered to have completely independent sources, but when their magnitudes are almost the same, that is, 2=! 2=VW2, the output terminal 15 becomes .

Therefore, the signal-to-noise ratio is improved by 3 dB compared to when PLLlO and PLLl are used alone. In FIG. 6, the delay circuit [2] and the high frequency correction circuit 13 can be omitted when the disturbance in the frequency characteristics due to the delay time difference between the PLLs [0 and 11] and the difference in the high frequency characteristics is within a permissible value.

Furthermore, when two or more PLLs are used, a similar circuit configuration can be achieved, and the noise can be further improved depending on the number of PLLs.

As described above, the present invention uses a PLL having a wide lock range and 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 the demodulated signal of the angle-modulated wave signal is obtained by using at least one PLL of each type and adding their demodulated outputs, a lot of energy is distributed in the middle and low frequencies of the angle-modulated wave signal. It is possible to reduce the level of distortion and noise occurring in the demodulated output due to the apparent overmodulation phenomenon caused by the modulated signal and the interference from the direct wave signal band to the angle modulated wave signal band.

It also has the advantage that the degree of reduction can be selected depending on the number of PLLs used.

[Brief explanation of the drawing]

Figure 1 is a block system diagram of an example of a PLL, and Figure 2 is a block diagram of an example of a PLL.
FIG. 3 is a diagram showing the frequency characteristics of FIG. 2, FIG. 4 is a diagram showing the lock range characteristics of an example of PLL, and FIG. A,
B is a demodulated signal waveform diagram of the high range and mid-low range of the conventional PLL,
FIG. 6 is a block diagram of an embodiment using two PLLs according to the present invention. 9... Angle modulated wave signal manual terminal, 10...
...PLL with wide lock range, 12...
... Delay circuit, 11 ... PLL having a narrow lock range, 13 ... High frequency correction circuit, 1
4...Addition circuit, 15...Output terminal.

Claims (1)

[Claims] 1. 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 signal having a relatively wide lock range characteristic is used. At least one locked loop and at least one phase-locked loop with relatively narrow lock range characteristics are provided, and these phase-locked loops are
The angle modulated wave signal to be demodulated is added to the loop to perform demodulation, and the demodulated outputs of these phase-locked loops are added to obtain a demodulated signal of the angle modulated wave signal with reduced distortion. Features a multi-channel record demodulation method. 2. In the multi-channel record demodulation method described in claim 1, the demodulated output of a phase-locked loop with relatively narrow lock range characteristics is supplied to the adder circuit via the frequency correction circuit, and The demodulated output of the phase-locked loop with lock range characteristics is supplied to the adder circuit via the delay circuit, and the frequency characteristics and delay times of each demodulated output are matched and then added to obtain a demodulated signal with flat frequency characteristics. A multi-channel record demodulation method characterized by: