JPS6028440B2 - Distortion detection method in multi-channel record playback device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a distortion detection method in a multi-channel record playback device, and relates to a method for detecting distortion in a multi-channel record playback device. A distortion detection method that can easily and accurately identify distortion (abnormal sounds) that may occur in a demodulated signal from musical sounds by detecting a predetermined frequency component of the envelope after being conveyed during demodulation of a wave signal. The purpose is to provide.

A multi-channel audio signal is converted into a direct wave signal and an angle-modulated wave signal, and these two signals are multiplexed and recorded in a single groove. When demodulating a wave signal, distortion (abnormal sound) that adversely affects musical tones may occur in the demodulated signal.

The causes of this distortion (abnormal sound) include dust attached to the record, scratches, stylus skipping, interference waves jumping from the direct wave signal band to the angle modulated wave signal band, or carriers generated due to these. - Possible cases include a drop or a case where the frequency shift of the modulated signal is larger than the predetermined frequency band.
In order to detect the above distortion (abnormal sound), a voltage controlled oscillator (VCO) that constitutes a phase-locked loop (PLL) for demodulating the reproduced angle-modulated wave signal has conventionally been used.
) and an input angle-modulated wave signal.

Here, as is well known, in PLL, the output signal of the VCO, which is transmitted at the carrier frequency of the input angle-modulated wave signal, and the input angle-modulated wave signal are respectively applied to a phase comparator, and a signal proportional to the phase difference between them is generated. After taking out the signal, it is added to a low-pass filter, and the output is supplied as a control voltage of the VCO, so that the phase of the output signal of the VCO is locked to the phase of the angle-modulated wave signal, and the The demodulated signal is extracted from the castle filter. In this case, the output of the VCO is P
When the input angle modulated wave signal of the LL is within the range of 0 to 1800 centered around 90o, the PLL is in a locked state and performs normal demodulation operation. However, due to the reasons mentioned above, when this phase difference exceeds the range of 0 to 180 degrees, the PLL becomes out of lock, causing distortion (
(abnormal noise) occurs. Conventionally, in order to remove this distortion, a phase comparator compares the phase of a signal obtained by shifting the phase of the output signal of the VCO constituting the upper PLL by 900 degrees and the input angle-modulated wave signal (synchronous detection). The output signal was used to detect the locking of the PLL. According to this method, almost 100% of occurrences of distortion (abnormal sounds) can be detected. However, the output of the above synchronous detector is V
The phase difference between the CO output signal and the input angle modulated wave signal is 0.
Even during normal reproduction within the range of ~180°, a signal corresponding to the phase difference is generated due to its configuration.

Therefore, especially in the case of a trumpet sound or the like in which the modulation signal has a large frequency shift, the output of the synchronous detector becomes extremely large. Therefore, when detecting distortion using a synchronous detector and controlling a circuit that mutes the demodulated signal with the detection signal in order to remove the above distortion, setting the threshold value may prevent muting malfunctions. Another problem was that it was extremely difficult to set a threshold value for minimum necessary and sufficient muting. The present invention eliminates the above-mentioned drawbacks, and embodiments thereof will be described below with reference to the drawings.

Figure 1 shows an example of the frequency spectrum of the envelope of the reproduced signal of the angle-modulated wave band when the demodulated signal of the angle-modulated wave signal reproduced from a multi-channel record is normal. An example of the spectrum of the frequency of the envelope of the reproduced signal of the angle modulated wave signal band when distortion (abnormal sound) occurs in the demodulated signal of the angle modulated wave signal is shown. Here, "the reproduced signal of the angle-modulated wave signal band" refers to a signal that collectively refers to the angle-modulated wave signal reproduced from a multi-channel record and the distortion components that may be mixed therein. , hereinafter referred to as a reproduced angle modulated wave signal. Note that the frequency spectrum of the envelope shown in FIGS. 1 and 2 is an example, and its shape naturally takes various forms depending on the state of the envelope. However, when the demodulated signal is normal, the frequency component around 10 KHz of the envelope of the reproduced angle-modulated wave signal is at a relatively low level, as shown by a in Figure 1. When a sound) is included, the envelope of the reproduced angle-modulated wave signal is at an extremely high level, as shown by a' in Figure 2, and there is a significant level difference between the two (at least higher than that of a pillow). This relationship holds true.

The significant level difference in the frequency components of the envelope of the reproduced angle-modulated wave signal near one Hz is thought to be caused by the following reasons.

In other words, since the series of transmission systems from the record recording system to the playback system is a non-linear transmission system, the signal demodulated through this transmission system undergoes amplitude modulation and generates distortion.
It is known that second-order harmonic distortion is the most common type of distortion. Also, although there are some differences in the energy component of this distortion depending on the characteristics of the pickup cartridge, it tends to increase as the height of the distortion increases. On the other hand, the energy component of a signal recorded on a multi-channel record usually increases to 4. The contact point between these two has a frequency around 10K. Therefore, distortion in the signal reproduced from the record occurs extremely often at frequencies around 20 KHz, which is the second harmonic. Therefore, the carrier wave of the angle modulated wave signal is 20
When amplitude modulation is caused by distortion around KHz, and the carrier frequency is selected to be, for example, 3 Hz, the frequency component of the envelope of the reproduced angle-modulated wave signal is the frequency component around 10K, which is the difference between the two. It occurs extremely frequently. (Furthermore, the frequency component near the 50K ratio, which is the sum component, hardly occurs due to the characteristics of the pickup cartridge.) This phenomenon in which the 10KHz component of the envelope of the reproduced angle-modulated wave signal increases significantly when distortion is mixed in is due to the following: This can be seen in all causes of distortion (abnormal noise) in the demodulated signal.On the other hand, if the demodulated signal is normal, even if the demodulated signal is a signal with a large frequency deviation such as a trumpet sound, This phenomenon is not observed.

The present invention has focused on the above-mentioned phenomenon, and has made it possible to accurately detect distortion (abnormal sounds) and to easily set the threshold value of a protection circuit such as a muting circuit.

FIG. 3 shows a block diagram of an embodiment of the method of the invention.

In the figure, a reproduced angle modulated wave signal from a multi-channel record inputted from an input terminal 1 is amplified to a predetermined value by an amplifier 2 and then supplied to an AM detector 3, where its envelope is detected. Ru. This envelope detection signal is applied to a narrow band filter 4 (for example, a 10 KHz filter), from which only frequency components at the 10 K range and its vicinity are filtered and extracted from the output terminal 5. When an angle-modulated wave signal that provides a normal demodulated signal is input to input terminal 1, its envelope is only slightly amplitude modulated by the nonlinear transmission system, so a minute signal is output to output terminal 5. appears. On the other hand, when a reproduced angle-modulated wave signal that gives a demodulated signal containing distortion (abnormal sound) enters the input terminal 1, the frequency component around 10 KHz in its envelope becomes extremely large for the reason mentioned above. 5, a significantly large signal appears. Since these two signals have a large level difference, they can be easily distinguished, and by using this signal as a control signal to operate a protection circuit such as a muting circuit, distortion (abnormal noise) can be detected in the demodulated signal. It is possible to provide a minimum necessary and sufficient protective response against so-called distortion (abnormal noise), which operates only when it occurs.

Therefore, by using this signal, it is easy to set the threshold value of a protection circuit such as a muting circuit, and by operating the protection circuit with this signal, distortion (abnormality) can be achieved without adversely affecting the musical tone. It is possible to obtain a demodulated output that does not include sound). As described above, the distortion detection method in the multi-channel record playback device according to the present invention is based on the method of detecting distortion in the multi-channel record playback device according to the present invention. a detection circuit that detects an envelope of a reproduced signal of the angle-modulated wave signal band when demodulating the angle-modulated wave signal;
It consists of a filter circuit that waves the difference between the carrier frequency of this angle-modulated wave signal and a frequency near pine Hz, and its nearby frequency components, and the angle-modulated wave signal is controlled by the level of the output signal of this filter circuit. Since the presence or absence of distortion occurring in the demodulated wave signal is detected, distortion that may occur in the demodulated signal due to carrier drop, interference distortion of the direct wave signal with the angle-modulated wave signal, etc. Abnormal sounds) can be easily and completely identified and detected as musical sounds, and since the level difference between normal and abnormal states is large, threshold values for protection circuits such as muting circuits can be easily set, and protection can therefore be easily detected. Malfunction of the circuit can also be prevented, and by controlling the operation of the protection circuit using the frequency component as a control signal, it is possible to obtain a demodulated output that does not include distortion (abnormal sounds) without adversely affecting the musical tone. It has characteristics such as:

[Brief explanation of the drawing]

Figure 1 is a diagram showing an example of the frequency spectrum of the envelope of the reproduced signal of the angle-modulated wave band when the demodulated signal of the angle-modulated wave signal reproduced from the multi-channel record is normal. Distortion (abnormal sound) in the demodulated signal of the angle modulated wave signal played from the record
FIG. 3 is a block system diagram of an embodiment of the method of the present invention. 1... Reproduced angle modulated wave signal input terminal, 3... AM
...Detector, 4...Band filter. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. When demodulating the angle modulated wave signal reproduced from a multichannel record where the multi-channel signal is a direct wave signal and an angle modulated wave signal, and these are multiplexed and recorded, the angle modulated wave signal band is It consists of a detection circuit that detects the envelope of the reproduced signal, and a filter circuit that filters the difference between the carrier frequency of the angle-modulated wave signal and a frequency around 20 KHz and frequency components in the vicinity thereof, and the output signal of the filter circuit 1. A method for detecting distortion in a multi-channel record reproducing apparatus, characterized in that the presence or absence of distortion occurring in a demodulated signal of the angle-modulated wave signal is detected based on the level of the angle-modulated wave signal.