JPS5934038B2 - Abnormal sound detection method in multi-channel record playback equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a phase modulator having a wide 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. It has at least one locked loop (hereinafter abbreviated as PLL) and one PLL with a relatively narrow lock range, and prevents interference waves generated during demodulation output from the direct wave signal band to the angle modulated wave signal band. The apparent overmodulation phenomenon caused by the abnormal sound (including distortion) and the modulation signal with a frequency deviation larger than the lock range, where much energy is distributed in the middle and low frequencies of the angle-modulated wave signal. A synchronous detector that is connected to a PLL with a wide lock range and generates an output signal according to the phase difference between the input signal and a voltage-controlled oscillator (hereinafter referred to as VCO), and a narrow lock range, are used to detect the abnormal noise that is the cause of the noise. A synchronous detector with a similar configuration connected to a PLL with
This paper proposes a method for detecting abnormal sounds by using each method separately.

As is well known, a PLL is used to demodulate an angle modulated wave signal recorded on a multi-channel record.

This PLL applies the output of a VCO that freely oscillates at the carrier frequency of the input angle-modulated wave signal and the input angle-modulated wave signal to a phase comparator, extracts a signal proportional to the phase difference between them, and then outputs this signal. is added to a low-pass filter, and its output is supplied as a control voltage of the VCO, so that the phase of the output of the VCO is locked to the phase of the angle-modulated wave signal, and the demodulated signal is obtained from the low-pass filter. It will be done. In this case, when the output of the VCO is within the range of 0 to 1800 centered around 900 with respect to the input angle modulated wave signal of the PLL, the PLL is in a locked state and performs a normal demodulation operation. However, due to interference waves jumping from the direct wave signal band to the angle modulated wave signal band, this phase difference is
When the range of 180 waves is exceeded, the PLL becomes out of lock and abnormal noise occurs during demodulation output. So this P
In order to detect the loss of lock of LL, the phase of the signal obtained by shifting the phase of the output of CO that constitutes PLL by 900 and the input angle modulated wave signal is compared by a phase comparator (synchronous detection).
However, it is possible to use this output signal to control the loop gain of the PLL, control the lock range of the PLL, or control a muting circuit or the like to detect and reduce abnormal sounds in the demodulated output. The PLL out-of-lock state that causes abnormal noise is caused by interference waves from the direct wave signal band to the angle-modulated wave signal band, and is caused by interference waves that are larger than the lock range where a lot of energy is distributed in the middle and low frequencies. There are two types: one is due to an apparent overmodulation phenomenon due to the modulation signal of the angle-modulated wave signal having a frequency shift, and the former is likely to occur in PLLs with a wide lock range, and the latter is likely to occur in PLLs with a relatively narrow lock range. . As an example, when the output of a phase comparator for synchronous detection (hereinafter referred to as a synchronous detector) goes out of lock, the DC level of the output increases; on the other hand, when the PLL goes out of lock, the DC level of the output increases. A case will be described in which the level is lowered (hereinafter, unless otherwise specified, a synchronous detector having such a configuration will be described).

The form of this rise and fall of the DC voltage (output waveform of the synchronous detector) differs depending on the lock range of the PLL, as will be described later. Therefore, when demodulating an angle-modulated wave signal with one PLL having a synchronous detector, and with the lock range changing, the output signal of the synchronous detector will change depending on the lock range, so the PLL will go out of lock. could not be detected accurately. The present invention solves the above-mentioned drawbacks and provides an abnormal sound detection method capable of accurately detecting lock loss.The present invention will be described below with reference to the drawings.

FIG. 1 is a diagram for explaining the principle of the present invention, and shows an example of a block system diagram of a PLL having a synchronous detector.
In the figure, 1 is an input terminal to which an angle-modulated wave signal is supplied, 2 is a phase comparator, 3 is a low-pass P wave detector, 4 is a CO, 5 is a synchronous detector, 6 is a demodulation output terminal, and 7 is a synchronization This is a detection signal output terminal.

As shown in the figure, the angle-modulated wave signal supplied to the input terminal 11 is phase-compared with the output signal of CO4 in the phase comparator 2, and the comparison detection output is passed through the low-band P-wave unit 3 as a demodulated output. It is taken out from the demodulation output terminal 6, and
Controls the oscillation phase and frequency of VCO4.

On the other hand, a part of the angle modulated wave signal from the input terminal 1 is also supplied to the synchronous detector 5, where the output signal of CO4 is
The signal is synchronously detected with the 00 phase shifted signal, and the synchronously detected output signal is taken out from the output terminal 7. The error voltage taken out from the output terminal 7 is the phase difference φ between the phase φ1 of the input signal applied to the input terminal 1 and the phase φ2 of the output of CO4.
This is caused by φ1−θ, and when the frequencies of the two signals match, the phase difference φ is 90° due to the principle of the phase comparator 2, and the error voltage at this time is 0. On the other hand, the output of the synchronous detector 5 is generated by the phase ψ1 of the input signal and the phase φ6-ψ of a signal obtained by shifting the output of CO4 by 90 degrees, and the phase difference G=ψ1-φ2 of ±90. φ here? The symbol above depends on the loop gain of the PLL. In other words, above 2
When the frequencies of the signals match, the phase difference is 00 (or 180), and at this time, the DC component of the signal corresponding to the synchronization with the input signal is 0. When there is a cause in the input signal that causes abnormal noise during demodulation output, that is,
The phase difference ψ changes greatly with respect to 900, and the phase comparator 2
When a more linear error voltage is no longer generated, the phase difference also changes greatly with respect to 00 (or 180, etc.), and a signal with a voltage larger than that of the synchronous detector 5 is generated.

An abnormal carrier is generated due to interference waves from the direct wave signal band to the angle modulated wave signal band, and this abnormal carrier is used as a PLL signal.
When applied as an input to a PLL, abnormal noise may occur in the demodulated output of a PLL having a wide lock range.

A wide rotary range means a large loop gain and a fast transient response. Therefore, the ability to follow the frequency of the modulated signal becomes faster, and the response to abnormal carriers also becomes faster. This means that the phase difference between the output and input of VCO4 is 9.
00 is large. In other words, this means that the percentage of time in which the phase difference between the input and the output of the VCO shifted by 90 is 00 (or 1800) is large. Therefore, the pulse density of the output signal according to the synchronization with respect to the input of the synchronous detector 5 is small, and the DC component is also small. An example of the waveform is shown in FIG. 2a. FIG. 2a is a diagram showing an example of the signal waveform of the synchronous detector 5 when an abnormal sound occurs during output of the demodulated signal due to an interference signal from the direct wave signal band to the modulated wave signal band. , 1 is a case where an abnormal sound occurs in a PLL with a wide lock range, and 2 is a case where a PL with a narrow lock range for the same signal is generated.
It belongs to L.

On the other hand, abnormal noise occurs in the demodulated output of the PLL, which has a lock range narrower than the frequency deviation of the modulated signal in which much energy is distributed in the middle and low frequencies.

A narrow lock range means a small loop gain and slow transient response. Therefore, the ability to follow the frequency of the modulation signal becomes slow, and the response to apparent overmodulation phenomena also becomes slow. This sets the input and VCO output to 90
The phase difference with the one with 0 phase shift is 0 output (or 18
00) is small.
Therefore, the pulse density of the output signal of the synchronous detector is large, and the DC component is large. An example of this waveform is shown in FIG. 2b. Second
Figure b shows what happens when abnormal noise occurs in the demodulated output due to an apparent overmodulation phenomenon caused by the frequency deviation of the modulation signal, which has a lot of energy distributed especially in the mid-low frequency range, which is larger than the lock range of the PLL. 2 is a diagram showing an example of a signal waveform of the synchronous detector 5, in which P2 has a narrow lock range.
This is a case where an abnormal sound occurs in the LL, and 1 is for a PLL having a wide lock range for the same input signal.

However, when interference waves from the direct wave signal band to the angle-modulated wave signal band are applied to a PLL having a narrow lock range, the output of the CO will lock to the interference wave due to the slow high frequency tracking of this PLL. The interfering waves disappear before this occurs, and abnormal sounds are almost never generated in the demodulated signal.

As mentioned above, although the abnormal sounds are the same in terms of phenomenon, the causes of their occurrence are different, and the signals detected by each synchronous detector are also different.

Therefore, abnormal sounds cannot be detected in a true sense without using a PLL having a plurality of synchronous detectors.

FIG. 3 shows an embodiment of an abnormal sound detection method according to the present invention and a multi-channel record demodulation method using the same.

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 10, respectively. PLL9 has a lock range that is equal to or wider than the maximum shift frequency range of the modulation signal of the angle modulated wave signal, and PLL1O has a lock range that is narrower than PLL9. PLL9 performs demodulation with little distortion for modulated signals such as trumpet sounds in which a lot of energy is distributed especially in the middle and low frequencies, but there is no interference from the direct wave signal band to the angle modulated wave signal band. Abnormal noises caused by the splashing of waves may occur. However, this abnormal sound, that is, the out-of-lock state, is caused by the synchronous detector 11 in the PLL 9.
A control circuit 12 including an integrating circuit and a differentiating circuit operates a controlled circuit 13 including a muting circuit, an attenuation circuit, etc., and the demodulated output containing the abnormal sound is controlled. PLLIO reduces abnormal noise caused by interference from the direct wave signal band to the angle modulated wave signal band due to its slow high frequency response.
In particular, abnormal noise is generated by a modulated signal having a frequency deviation larger than the lock range, in which a large amount of energy is distributed in the middle and low frequencies. However, this abnormal sound is PL
It is quickly detected by the synchronous detector 14 in the LlO, and by the control circuit 15, for example, by a cascaded differentiating circuit, etc.
For example, a controlled circuit 16 such as a muting circuit or an attenuation circuit is operated to control the demodulated output containing the abnormal sound. The outputs of the controlled circuits 13 and 16 are applied to an adder circuit 17, and a demodulated signal of the angle-modulated wave signal is taken out from an output terminal 18. For example, a case where a muting circuit is used for the controlled circuits 13 and 16 will be described below.

When no abnormal sound is generated in the demodulated outputs of the PLLs 9 and 10, the demodulated signal of the reproduced angle-modulated wave signal is the sum of the demodulated outputs. When an abnormal sound occurs in the demodulated output of the PLL 9 due to interference waves jumping from the direct wave signal band to the angle-modulated wave signal band, the muting circuit 13 sets the demodulated output of the PLL 9 to 0FF, and the reproduced angle-modulated wave The demodulated signal of the signal becomes the demodulated output of PLLIO. That is, although the output level is reduced by 6 dB, no abnormal sound appears in the demodulated signal. The same is true when an abnormal sound is generated during the demodulated output of the PLLIO due to a frequency shift of the modulation signal, in which a large amount of energy is distributed in the middle and low frequencies wider than the lock range of the PLLIO. In FIG. 3, the disturbance in the frequency characteristics of the demodulated output that is added due to the difference in delay time and the difference in high frequency characteristics between PLLs 9 and 1O is as follows.
When it is not within the tolerance, a delay circuit is connected to the output of PLL9, and the PLL
Add a high frequency correction circuit to the output of IO.

It is also obvious that when two or more PLLs are used, the occurrence of abnormal noise can be dealt with in detail depending on the number of PLLs.

In addition, in FIG. 3, 19 and 20 are phase comparators, 21,
22 is a low-frequency P wave device, and 23 and 24 are COs.

Furthermore, since the operations of PLL 9 and IO are the same as in the case of FIG. 1, the explanation thereof is omitted.

The present invention is a multi-channel system in which direct wave signals and angle-modulated wave signals are multiplexed and recorded. When demodulating an angle-modulated wave signal reproduced from a record, by using at least one PLL with a wide lock range and one PLL with a relatively narrow lock range, each equipped with a synchronous detector, it is possible to It is possible to completely detect abnormal sounds that occur during the demodulated output due to the apparent overmodulation phenomenon due to the modulation signal with a large distribution of energy and interference from the direct wave signal band to the angle modulated wave signal band. By using the output signal, it is possible to obtain a demodulated output that does not contain abnormal sounds.

[Brief explanation of the drawing]

Fig. 1 is a block system diagram of an example of a PLL equipped with a synchronous detector, Fig. 2 is a diagram showing an example of the signal waveform of the synchronous detector when an abnormal sound occurs during demodulation output, and Fig. 3 The figure is a block system diagram of one embodiment of the present invention. 8... Angle modulated wave signal input terminal, 9...
・・PLLllO with wide lock range・・・・
・PLL with narrow lock range, 11, 14...
... Synchronous detector, 13, 16 ... Controlled circuit, 12, 15 ... Control circuit, 17 ...
Adder, 18... Demodulation output terminal, 19, 20...
... Phase comparator, 21, 22 ... Low range P
Wave device, 23, 24...VCO.

Claims (1)

[Claims] 1. When demodulating the angle modulated wave signal reproduced from the multi-channel record where the direct wave signal and the angle modulated wave signal are multiplexed and recorded, a phase locked loop with a relatively wide lock range characteristic; Each of these phase-locked loops has at least one phase-locked loop with a relatively narrow locking range characteristic, and each of these phase-locked loops has a -Equipped with a synchronous detector that generates an output according to the phase difference with the phase of the oscillation output of the voltage controlled oscillator in the loop, and adds the angle modulated wave signal to be demodulated to these phase locked loops. Demodulation is performed, and the presence of abnormal sounds generated in the demodulated signal is detected using the signals obtained from these synchronous detectors, and the abnormal sounds in the demodulated signals are removed using the detection output. Abnormal sound detection method for multi-channel record playback equipment.