JPH0481175A - Ghost noise elimination system for television signal - Google Patents

Abstract

PURPOSE:To reduce the effect of ghost noise to both a video signal and an audio signal by passing a detection signal in a video intermediate frequency through a ghost noise elimination circuit before being separated into the video signal and the audio signal in the ghost noise elimination method using a GCR signal. CONSTITUTION:A filter coefficient is set in a direction that ghost of a GCR signal resident in an output signal of a transversal filter 65 is lost. The correction is implemented repetitively every time a GCR waveform fetch memory 66 reads the GCR signal. As a result, filter coefficients C1-Cn of each multiplier are set every time the differential ghost of the GCR signal is finally canceled out and ghost noise is eliminated from a digital detection signal outputted from an adder circuit 72. Then the above detection signal is fed to a D/A converter 67, in which the signal is converted into an analog signal and fed respectively to an audio trap circuit 3 and a band pass filter 4, in which the signal is separated and demodulated into the video signal and the audio signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a ghost noise removal method for television signals using GCR signals.

[Conventional technology]

As a countermeasure against ghosts in television broadcast reception, there is a ghost noise removal method using a GCR signal (noise removal reference signal). The GCR signal is a reference signal for detecting the position and magnitude of ghost noise mixed into a television signal.
) and the 281st horizontal scanning period (281H). Conventionally, ghost noise in a video signal has been removed using this GCR signal in the following manner.

That is, a ghost noise removal circuit configured using a digital filter such as a transversal filter is attached to the video signal path after separating the video signal and audio signal, and is inserted in the horizontal scanning periods 18H and 281H. Ghost noise in the video signal is removed by determining the position and size of the ghost from the GCR signal and adjusting the filter coefficients of the transversal filter so that the ghost component of the GCR signal is canceled out and removed. .

[Problem to be solved by the invention] By the way, ghost noise mixed into a television signal has a negative effect not only on the video signal but also on the audio signal, and ultimately becomes a multipath disturbance for the audio. appear. However, as described above, ghost noise countermeasures have conventionally been taken only for video signals, and currently no countermeasures have been taken for audio signals.

This is considered to be due to the following reasons.

In other words, as is well known, the audio signal of television broadcasting uses the FM modulation method, and when ghost noise is mixed into this FM audio signal, the audio signal is distorted by being subjected to both amplitude modulation and phase modulation, but the amplitude For modulation components, FM
Since the ghost noise is automatically removed by the limiter action of the detection circuit, the influence of ghost noise on the audio is limited to the phase modulation component. For this reason, the influence of ghost noise on audio is considerably smaller than on video, and it is thought that it has been largely overlooked in the past.

However, in order to reproduce higher quality images and audio in receiving television broadcasts, it is more desirable to eliminate the influence of ghost noise not only on the video signal but also on the audio signal.

The present invention was made under the above circumstances, and its purpose is to provide a ghost noise removal method for television signals that can reduce the influence of ghost noise on both video and audio. That's true.

[Means to solve the problem]

In order to achieve the above object, a first invention provides a ghost noise removal method using a GCR signal in an intercarrier type TV tuner, in which ghost noise is removed before separating a detected signal of a video intermediate frequency into a video signal and an audio signal. It is designed to pass through a removal circuit.

The second invention is a ghost noise removal method using a GCR signal in a split carrier type TV tuner, after separating a video intermediate frequency detection signal into a video signal and an audio signal, and then converting each signal into its own signal. The filter coefficients obtained by the ghost noise removing circuit for video signals are used as the filter coefficients for the ghost noise removing circuit for audio signals.

In the case of this second invention, taking into account that the digital processing focus numbers of video signals and audio signals are different, the filter coefficients obtained by the ghost noise removal circuit for video signals are used to remove ghost noise for audio signals. It is desirable to convert the coefficients into filter coefficients suitable for the circuit and then send them to the ghost noise removal circuit for audio signals.

[Function] In the case of the first invention, ghost noise from both the video signal and the audio signal can be removed at once by a single ghost noise removal circuit.

Further, in the case of the second invention, noise removal processing is performed independently for each video signal and audio signal, but the filter coefficients obtained by the ghost noise removal circuit for the video signal are applied to the filter coefficients of the ghost noise removal circuit for the audio signal. By using it as a coefficient, ghost noise can be removed from an audio signal without a GCR signal in the same way as from a video signal.

〔Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a first embodiment of the invention.

This first embodiment corresponds to the first invention described above, and is an example of the case where the ghost noise removal method of the present invention is applied to an intercarrier TV tuner.

Note that the intercarrier method is a method that does not use a dedicated local oscillator when demodulating audio signals from video intermediate frequency signals.
This is an audio demodulation method that uses the carrier of the video intermediate frequency signal, which has a 4.5 MHz difference from the audio signal, as a local oscillation frequency, and demodulates the audio signal at the same time as the video signal.

In Fig. 1, a video intermediate frequency (PIF) circuit 1 is a circuit that performs signal processing such as IF filtering, IF amplification AGC, and AFT on the video intermediate frequency signal sent from the front end (FE). The output signal is sent to the video detection circuit 2.

The video detection circuit 2 is a circuit that performs synchronous detection on the video intermediate frequency signal, and simultaneously demodulates the video signal using its carrier of 58.75 MHz, and simultaneously detects the 4.5 MHz signal from the video signal.
Audio signal z away (58, 75-54, 25-4, 5M
Hz). Then, the detected signal containing the video signal and audio signal is passed through a 4.5 MHz audio trap circuit 3 to obtain a video signal. Also, 4.5 MHz
After passing through a band pass filter (BPF) 4, the audio signal is detected by an audio detection circuit 5 to obtain an audio signal.

The first embodiment is a TV using such an intercarrier system.
In the tuner, a ghost noise removal circuit 6 using a GCR signal is attached after the video detection circuit 2, and the ghost noise of both the video signal and the audio signal is removed at once.

A specific example of the configuration of the ghost noise removal circuit 6 is shown in FIG.

In FIG. 2, an input terminal 61 is a terminal to which a detection signal is input from the video detection circuit 2 of FIG. 63 and a synchronization separation circuit 64 that separates horizontal and vertical synchronization signals in the video signal. The output of the A/D converter 62 is input to a transversal filter 65 for ghost removal. Also,
The output of the transversal filter 65 is connected to a D/A converter 67 and is also input to a GCR waveform acquisition memory 66.

The output of the D/A converter 67 is transmitted to the audio trap circuit 3 and the bandpass filter 4 in FIG.
are entered respectively. In addition, the clock generation circuit 4
The clock CK output by the circuit is given to each circuit as a reference signal.

The timing generation circuit 68 is a circuit that generates various timing signals based on the clock CK output from the clock generation circuit 63 and the horizontal synchronization signal H and vertical synchronization signal (2) separated by the synchronization separation circuit 64.

The arithmetic circuit 69 calculates a filter coefficient C for removing the ghost noise component remaining in the output signal of the transversal filter 65 from the delay time and amplitude of the ghost noise component of the GCR signal captured in the GCR waveform capture memory 66. , -Cn are calculated and supplied to the transversal filter 65.

FIG. 3 shows a specific circuit example of the transversal filter 65.

In FIG. 3, the transversal filter 65 is
A plurality of delay elements 651a to 651n are configured to take out sequentially delayed input signals for every fixed delay time τ, and a desired signal is obtained by multiplying the tap output of each delay element by a predetermined filter coefficient C1 to Cn, respectively. It consists of a plurality of multipliers 652a to 652n that provide tap gains, and an adder circuit 653 that adds the outputs of these multipliers to each other to obtain a total sum. When filter coefficients C3 to Cn of each multiplier 652a to 652n are appropriately set,
A signal from which ghost noise has been removed is obtained as the output of the adder 653. Filter coefficients C and -Cn of each multiplier 652a to 652n are supplied from the arithmetic circuit 69 in FIG. In the case of the circuit example shown in FIG. 3, the filter coefficient CI is set to 1, and the original waveform containing ghost noise is sent from the delay element 651a to the addition circuit 653, and the ghost noise component contained in this original waveform is The values of the other multiplication coefficients C2 to Cn are set so that the value becomes 0.

In the configurations shown in FIGS. 2 and 3, the input terminal 61
When a detection signal of a video intermediate frequency signal is input from the video detection circuit 2 shown in FIG.
The signal is converted into a digital signal at the transversal filter 65 and input to the transversal filter 65. On the other hand, the detected signal that has passed through the transversal filter 65 is sent to the D/A converter 6.
7 and input into the GCR waveform acquisition memory 66. The GCR waveform capture memory 66 captures synchronization signals at positions of horizontal scanning periods 18H and 218H of the video signal in the detection signal sent from the transversal filter 65 based on the timing signal generated by the timing generation circuit 68. .

The captured synchronization signal is then sent to the arithmetic circuit 69, where a difference calculation between it and the internally generated GCR signal is performed, and only the ghost component of the GCR signal is extracted. The arithmetic circuit 69 sets the filter coefficients C1 to Cn so that the ghost component of the extracted GCR signal is canceled out,
It is supplied to each multiplier 651a to 651n, respectively.

As described above, the filter coefficients are set in the direction in which the ghost of the GCR signal remaining in the output signal of the transversal filter 65 disappears, and this series of correction operations is performed by the GCR signal.
This process is repeated every time the CR waveform capture memory 66 reads a GCR signal. As a result, each multiplier 651a sets a value such that the difference ghost of the GCR signal is finally canceled out and disappears.
Filter coefficients C1 to Cn of ~651n are set, and the digital detection signal output from the adder circuit 72 becomes a signal from which ghost noise has been removed. The digital detection signal from which this ghost noise has been removed is sent to the D/A converter 67, where it is converted into an analog signal, and then sent to the audio trap circuit 3 and bandpass filter 4 shown in FIG. 1, respectively. In this way, the signal is separated and demodulated into a video signal and an audio signal.

FIG. 4 shows a second embodiment of the invention.

This second embodiment corresponds to the second invention described above, and is an example in which the ghost noise removal method of the present invention is applied to a split carrier type TV tuner. Note that the split carrier method is an audio demodulation method in which a dedicated local oscillator is used to separate the audio signal from the video intermediate frequency signal, and the audio signal is demodulated independently of the video signal.

In FIG. 4, a video intermediate frequency (PIF) circuit 1 is a first
This circuit is the same as the circuit shown in the figure, and its output signals are sent to a video detection circuit 7 and an audio detection circuit 8, respectively. The video detection circuit 7 demodulates the video multiplied signal from the video intermediate frequency signal. On the other hand, the audio detection circuit 8 demodulates the audio signal using a built-in local oscillator.

The second embodiment is based on the split carrier type T.
In the V-tuner, a ghost noise removal circuit 6 for video signals and a ghost noise removal circuit 9 for audio signals are provided after the video detection circuit 7 and audio detection circuit 8, respectively, and ghost noise removal circuits 6 for video signals and ghost noise removal circuits 9 for audio signals are provided. The configuration is such that the filter coefficients C1 to Cn obtained by the circuit 6 are used as filter coefficients of the ghost noise removal circuit 9 for audio signals.

The ghost noise removal circuit 6 for video signals has the same circuit configuration as that shown in FIG. 2 described above. On the other hand, the ghost noise removal circuit 9 for audio signals includes the A/D converter 62, transversal filter 65, and D/A converter 62 in the circuit shown in FIG.
Constructed using only a converter 67, the clock generation circuit 6
3. The synchronization separation circuit 64, GCR waveform capture memory 66, timing generation circuit 68, arithmetic circuit 69, etc. are omitted.

As is well known, a television signal is a composite signal of an amplitude modulated video signal and an FM modulated audio signal, and if ghost noise is mixed into this composite signal, the ghost noise will be present in both the video signal and the audio signal. They occur at the same time position. Therefore, even if a GCR signal like a video signal does not exist in the audio signal, the ghost noise removal circuit 6 for the video signal uses the filter coefficient C for ghost removal.
If ~Cn is obtained, the filter coefficient C for this video signal
Ghost noise in the audio signal can be removed by the audio signal ghost noise removal circuit 9 using I to Cn.

FIG. 5 shows a modification of the second embodiment. In the example shown in FIG. 5, the filter coefficient C1 obtained by the video signal ghost noise removal circuit 6 in the filter coefficient conversion circuit 10
~Cn are converted into filter coefficients C1 to Cn' suitable for the ghost noise removal circuit 9 for audio signals, and then sent to the ghost noise removal circuit 9 for audio signals.

Generally, when digital signal processing is applied to a television signal, the video signal has 8 bits per sample (2fi=2
It is sufficient to have about 56 gradations), but the audio signal requires about 16 bits, which is twice as many per sample. Therefore, when the number of processing vias is different between the video signal and the audio signal, as shown in FIG. It is desirable that the filter coefficient conversion circuit 10 converts the coefficients into coefficients suitable for the number of processing bits of the ghost noise removal circuit 9 for audio signals, and then sends them to the ghost noise removal circuit 9 for audio signals. Since it is considered that video signals and audio signals normally have different processing focus numbers, the circuit shown in FIG. 5 is more practical.

Note that the above embodiment uses an acyclic transversal filter (FIR filter) as a ghost noise removal circuit.
We took as an example a case using a recursive filter (II
It goes without saying that a similar configuration can be achieved using a filter (R filter). Further, although the sequential correction method is used as an example of the ghost removal algorithm, other methods such as the division method may also be used. Furthermore, in FIG. 1, the 4.5 MHz audio trap circuit 3 and BPF 4 pass the analog signal that has been D/A converted by the D/A converter 67 of the ghost noise removal circuit 6 in FIG. However, the audio trap circuit 3 and the BPF 4 may have a digital configuration, and after performing respective processing as digital signals, D/A conversion may be performed.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the influence of ghost noise can be removed from both the video signal and the audio signal, and high quality video and audio can be reproduced.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the first embodiment of the present invention, FIG. 2 is a configuration diagram of the ghost noise removal circuit in FIG. 1, FIG. 3 is a circuit diagram of the transversal filter in FIG. FIG. 4 is a block diagram of the second embodiment, and FIG. 5 is a block diagram of the circuit shown in FIG. DESCRIPTION OF SYMBOLS 1... Video intermediate frequency circuit, 2, 7... Video detection circuit, 3... Audio trap circuit, 4... Bandpass filter, 5.8... Audio detection circuit, 6, 9...・Ghost noise removal circuit, 65... Transversal filter, C3 to Cn... Filter coefficient, cl to Cn
...Converted filter coefficients.

Claims (3)

[Claims] (1) In the ghost noise removal method using GCR signals in intercarrier TV tuners, the video intermediate frequency detection signal is passed through a ghost noise removal circuit before being separated into the video signal and the audio signal. Ghost noise removal method for television signals. (2) In a ghost noise removal method using a GCR signal in a split carrier TV tuner, after separating the video intermediate frequency detection signal into a video signal and an audio signal, each signal is subjected to ghost noise removal for each signal. A ghost noise removal method for a television signal, characterized in that the ghost noise removal circuit for an audio signal passes through a ghost noise removal circuit and the filter coefficients obtained by the ghost noise removal circuit for the video signal are used as the filter coefficients for the ghost noise removal circuit for the audio signal. (3) In the ghost noise removal method according to claim (2), after converting the filter coefficients obtained by the ghost noise removal circuit for video signals into filter coefficients suitable for the ghost noise removal circuit for audio signals, A noise removal method for a television signal, characterized in that the signal is sent to a ghost noise removal circuit for audio signals.