JPH04134674A - Noise correction device - Google Patents

Abstract

PURPOSE:To surely correct a dropout by providing a digital signal processing means, a dropout detecting means and correcting means and so on. CONSTITUTION:A HiFi sound digital signal processing circuit 21 executes a reproduction digital process toward an inputted digital sound signal and outputs to a memory 3 as well as reads out the data of the memory 3, executes a prescribed digital process and outputs a terminal (b) of a switch 6. Thus, the regenerative signal of a HiFi sound is delayed at a prescribed period and applied to the switch 6. And when a detecting signal is inputted from a dropout detecting circuit 22, the circuit 21 prepares interpolation data for a linear interpolation while a dropout part is read out from the memory 3, and interpolates the dropout part by these interpolation data and outputs it. In this case, the delayed time by the memory 3 is comparatively long, a sure interpolation is possible, and it is possible to surely correct the noise due to the dropout and the lack of an envelope.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a noise correction device, and is particularly suitable for video tape recorders capable of PCM audio recording and h;rr audio recording, audio products, etc. The present invention relates to a noise correction device.

(Prior art) Conventionally, CD (compact disc player) and DA
In audio products such as T (digital audio tape recorder), playback signals are digitally processed and D/A
The signal is output after being converted to an analog signal using a (digital/analog) converter, and high-fidelity playback is possible through digital processing.

Even in 8mm VTR (video tape recorder), F
In addition to the old Fl audio mode that uses the M modulation recording method and the normal audio mode that uses the bias recording method, it has a PCM audio mode that performs digital processing.

FIG. 8 is a block diagram showing a conventional noise correction device employed in a VTR having such a PCM audio mode and an old [1 audio mode].

The PCM head 1 reproduces, for example, a digital audio signal recorded on a part of a recording track by tracing a magnetic tape (not shown), and supplies the reproduced signal to the PCM digital signal processing circuit 2. The PCM digital signal processing circuit 2 uses the memory 3 to digitally process the reproduced signal and outputs the audio signal to the D/A converter 4. The audio signal converted into analog by the D/A converter 4 is applied to the terminal a of the switch 6 via the output circuit 5.

On the other hand, the HRRI head 7 reproduces the FM analog audio signal recorded on the recording track of the magnetic tape over the video signal and supplies it to the old Fi audio analog signal processing circuit 8 . The HiFi audio analog signal processing circuit 8 subjects the reproduced signal to analog audio processing and supplies it to the terminal of the switch 6 via the sample hold circuit 9.

The reproduced signal is also given to the dropout detection circuit H1o. The dropout detection circuit 10 detects dropout of the reproduced signal and provides the detection signal to the sample hold circuit 9. When the sample and hold circuit 9 receives the detection signal, the HiFi audio analog signal processing circuit 8
The output is held and output to the terminal of switch 6.

As a result, the dropout portion is corrected to the value immediately before dropout. The switch 6 is switched according to the mode and outputs an audio signal from the terminal C to the line out terminal 11.

There are also VTRs that employ digital signal processing in HiFi audio mode. FIG. 9 is a block diagram showing a conventional noise correction device employed in such a VTR.

The reproduction signal from the old Fi head 7 is given to an A/D (analog/digital) converter 12.

The audio signal converted to digital by the A/D converter 12 is supplied to the old F1 audio digital signal processing circuit 13 and subjected to digital signal processing. Further, the signal is converted into an analog signal by the D/A converter 14 and provided to the sample and hold circuit 9. Other operations are similar to those in FIG.

In this way, in FIGS. 8 and 9, the digital signal processing system for the PCM audio mode and the analog or digital signal processing system for the HiFi audio mode audio mode are independently provided, allowing operation in each mode. I have to.

By the way, in these circuits, dropout detection circuit 1
The timing at which 0 detects dropout and the timing at which noise is mixed into the old Fi audio are approximately the same time. Because of this, when the sample and hold circuit 9 samples a signal using the detection signal, some noise is mixed into the interpolated signal by the sample and hold circuit 9.
There is a problem in that it is not possible to completely prevent noise from being mixed into the HiFi audio mode.

Also, when switching the playback speed, such as when switching between sp (standard) mode and EP (double speed) mode,
These circuits cannot completely prevent noise from being mixed in, even in the case of such dropouts where the envelope of HiFi audio is lost.

(Problem to be Solved by the Invention) As described above, the conventional noise correction device described above cannot reliably correct dropouts, and
There was a problem that noise occurred in i-voice.

The present invention has been made in view of such problems, and includes:
It is an object of the present invention to provide a noise correction device that can reliably correct dropouts.

[Structure of the Invention] (Means for Solving the Problems) A noise correction device according to the present invention includes a reproducing means for reproducing information recorded on a recording medium capable of recording using a digital method and an analog method, and a memory. A digital signal processing means for performing predetermined digital signal processing on the digital reproduction signal from the reproduction means using the memory and outputting the result, and A for converting the analog reproduction signal from the reproduction means into a digital signal. an A/D converter, a detection means for detecting dropout of the analog playback signal from the playback means and outputting a detection signal, and a detection means for detecting dropout of the analog playback signal from the playback means and outputting a detection signal; and a D/A converter that converts the output of the correction means into an analog signal. It is something.

(Function) In the present invention, the correction means delays the reproduced signal by transferring the output of the A/D converter to the memory used by the digital signal processing means to perform digital signal processing. Dropout of the reproduced signal is detected by the detection means. Based on the detection signal from the detection means, the correction means performs interpolation or approximation on the delayed reproduction signal to correct noise due to dropout.

In this way, even if noise is mixed in at approximately the same time as the detection means detects dropout, it is possible to reliably correct the noise.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of a noise correction device according to the present invention. This embodiment is applied to a dropout correction device for a VTR having a PCM audio mode. In FIG. 1, the same components as in FIG. 9 are given the same reference numerals.

The PCM head 1 reproduces a digital PCM audio signal recorded on a magnetic tape (not shown) and transmits the reproduced signal to a PC.
It outputs to the M digital signal processing circuit 2. The PCM digital signal processing circuit 2 utilizes the memory 3 to perform various digital processing such as error correction, and outputs a digital audio signal to the terminal a of the switch/7/chi 6.

On the other hand, the HiFi head 7 plays back an FM audio signal recorded on a magnetic tape (not shown), and the A/D converter 1
2 and the dropout detection circuit 22. A/D
The converter 12 converts the input analog FM audio signal into a digital signal and supplies it to the HiFi audio digital signal processing circuit 21 . The dropout detection circuit 22 detects dropout of the reproduced signal and converts the detected signal into Hl[
; Provided to the audio digital signal processing circuit 21.

The old Fi audio digital signal processing circuit 21 performs reproduction digital processing on the input digital audio signal and outputs it to the memory 3, and also reads data from the memory 3, performs predetermined digital processing, and outputs the data to the terminal of the switch 6. Output to As a result, the HiFi audio reproduction signal is delayed by a predetermined period and is then applied to the switch 6. When the HiFi audio digital signal processing circuit 21 receives a detection signal from the dropout detection circuit 22,
Until the dropout portion is read out from the memory 3, interpolation data for linear interpolation is created, and the dropout/knobout portion is mr511 with this interpolation data and output. The delay time caused by the memory 3 is relatively long, and reliable interpolation is possible.

Switch 6 selects terminals a and b according to the mode, and
One of the outputs from the M digital signal processing circuit 2 or the old Fi audio digital signal processing circuit 21 is selectively outputted from the terminal C to the D/A converter 23. The D/A converter 23 converts the input digital signal into analog,
The signal is output to the line out terminal 11 via the output circuit 24.

Next, the operation of the noise correction device configured as described above will be explained with reference to FIG. 2. Figure 2 (a) is the old Fi
The envelope of the reproduced signal of the head 7 is shown in FIG.
b) shows the waveform indicated by the digital data given to the memory 3 from the old Fi audio digital signal processing circuit 21, and FIG. 2(c) shows the digital data read out from the memory 3 to the old Fi audio digital signal processing circuit 21. 2(d) shows the detection signal, and FIG. 2(e) shows the waveform shown by the digital reproduction signal outputted from the old Fi audio digital signal processing circuit 21 to the switch 6. There is.

During playback in PCM mode, PCM head 1
The reproduced signal from the PCM digital signal processing circuit 2 and memory 3 undergoes error correction processing and the like. PCM
The digital audio signal from the digital signal processing circuit 2 is applied to the D/A converter 23 via the switch 6 and converted into an analog signal. In this way, an analog audio signal is output from the output circuit 24 via the line out terminal 11.

On the other hand, when playing in HiFi audio mode, )1
The reproduced signal from the +Fi head 7 is converted into a digital signal by the A/D converter 12 and is applied to the HiFi audio digital signal processing circuit 21. The HiFi audio digital signal processing circuit 21 performs predetermined reproduction processing on the input reproduced digital signal and outputs the digital signal shown in the waveform of FIG. 2(b) to the memory 3. In this case, as shown in FIG. 2(a), a drop error 1~ is generated in the reproduced signal. Due to this dropout, noise is mixed into the signal applied to the memory 3 (FIG. 2(b)).

The dropout detection circuit 22 provides a detection signal shown in FIG. 2(d) to the HiFi audio digital signal processing circuit 21 at the timing of occurrence of dropout. The HF1 audio digital signal processing circuit 21 creates interpolation data for linear interpolation at the timing of the detection signal, and interpolates the noise portion of the data read from the memory 3 (FIG. 2(C)) with the interpolation data. In this way, from the HiFi audio digital signal processing circuit 21, as shown by the thick line in FIG. 2(e),
Data with noise portions linearly interpolated is output. This data is applied to the D/A converter 23 via the switch 6, converted into an analog signal, and applied to the output circuit 24. The output circuit 24 outputs the old Fi audio from the line out terminal 11.

In this way, in this embodiment, the IiFi audio reproduction signal is delayed (using the memory 3 for digitally processing the PCM audio mode reproduction signal), and the dropout portion is converted into interpolated data using the delay time. It is interpolated with. Even if the dropout detection timing is relatively late, reliable interpolation is possible, and even if dropouts, envelope omissions, etc. occur, a reproduced audio signal with noise removed can be obtained.

Further, in place of the dropout detection circuit 22, a reproduction speed detection circuit may be provided for detecting the reproduction speed in SP mode, EP mode, or the like. In this case, interpolation data is created at the timing of the detection signal from the playback speed detection circuit, and the gaps in the playback envelope that occur due to changes in tape speed are interpolated using this interpolation data, thereby preventing the generation of noise. I can do it.

FIG. 3 is a block diagram showing a modification of the embodiment shown in FIG. 1. Note that in FIG. 3, the reproduction system circuit for the PCM audio mode is omitted. In FIG. 3, the same components as in FIG. 1 are given the same reference numerals, and their explanations will be omitted.

This embodiment is adopted for a VTR having a smooth mute function. The output of the u1rr audio digital signal processing circuit 21 is given to a D/A converter 25. D
/A converter 25 converts the interpolated reproduction signal into an analog signal and converts it into a voltage control amplifier (hereinafter referred to as VCA) 2.
Output to 6. On the other hand, the reproduction signal from the HiFi head is also given to the dropout detection circuit 27. The dropout detection circuit 27 detects dropout of the reproduced signal and outputs the detection signal to the VCA*1flJ times R28. When the CAI control circuit 28 receives the detection signal,
After a predetermined time, a gain control signal for controlling the gain of the VCA 26 is output to the CA 26. The gain of the VCA 26 is adjusted by this gain control signal.

FIG. 4 is a circuit diagram showing a specific configuration of the VCA 26.

The output of the D/A converter 25 is applied to the input terminal 30 . A resistor R1 is connected between the input terminal 30 and the line-out terminal 11, and the line-out terminal 11 is connected to the power supply terminal 32 via the resistor R2 and the source-drain path of the FET 31. A reference voltage vrer is applied to the gate of the FET 31 via a capacitor C, and a gain control signal is applied from the VCA control circuit 28 via a resistor R3.

In the VCA 26 configured in this way, the resistor R1
, R2 and the on-resistance of the FET 31 determine the gain. A reference voltage V ref is applied to the gate of the FET 31, and the FET 31 is in an on state.

Here, as the gain control signal from the VCA control circuit 28 changes, the on-resistance of the FET 31 changes, and the gain of the audio signal output to the line-out terminal 11 changes.

Next, the fifth section will explain the operation of the embodiment configured as described above.
This will be explained with reference to the figures. Figure 5(a) shows Hi Fi
5(b) shows the waveform indicated by the data input to the memory 3, and FIG.
C) shows the waveform indicated by the data read from the memory 3, FIG. 5(d) shows the detection signal, and FIG.
e) shows the gain control signal, and FIG. 5(f) shows the VCA26
FIG. 5(g) shows the waveform when applied to hard mute.

The HiFi audio digital signal processing circuit 21 is shown in FIG.
As shown in b) and (c), by transferring the data to the memory 3, the reproduced signal is delayed and provided to the D/A converter 25. The D/A converter 25 converts the reproduced signal into an analog signal and outputs it to the VCA 26. On the other hand, when the dropout detection circuit 27 detects dropout of the reproduced signal, it outputs a detection signal shown in FIG. 5(d) to the VCA control circuit 28. The VCA control circuit 28 is shown in FIG.
As shown in e), the level of the gain control signal is changed from high level to low level at a timing based on the timing of the detection signal. Then, the on-resistance of the FET 31 changes and the gain of the VCA 26 decreases. In this way, the line-out terminal 11 has the following information as shown in FIG. 5(f).
A playback signal with the dropout portion muted is output.

Note that if hard mute is used, the muted portion will produce step-like noise as shown in FIG. 5(g).

FIG. 6 is a block diagram showing another modification of the embodiment of FIG. 1. In FIG. 6, the same components as in FIG. 3 are denoted by the same reference numerals and their explanations will be omitted.

The output of the HiFi audio digital signal processing circuit 21 is given to a digital multiplier 35. The digital multiplier 35 multiplies the input digital signal by a coefficient based on the detection signal from the dropout detection circuit 27 and outputs the result to the D/A converter 36 . The D/A converter 36 converts the input reproduction signal into an analog signal and outputs the analog signal.

In the embodiment configured in this manner, the digital multiplier 35 adjusts the gain of the output of the old Fi audio digital signal processing circuit 21 at a timing based on the timing at which the detection signal is input, and outputs the adjusted signal. You can obtain an audio signal with the out part muted.

The seventh factor is a block diagram showing a noise correction device according to another embodiment of the present invention. This embodiment is an example applied to a dropout correction device for a VTR having a digital output terminal. In FIG. 7, the same components as in FIG. 1 are denoted by the same reference numerals, and their explanation will be omitted.

This embodiment differs from the embodiment shown in FIG. 1 in that a digital output signal processing circuit 40 is provided.

That is, the digital reproduction signal from the terminal C of the switch 6 is given to the D/A converter 23 and also to the digital output signal processing circuit 40. The digital output signal processing circuit 40 digitally processes the input reproduction signal and outputs it from a digital output terminal 41.

Further, in this embodiment, the PCM digital signal processing circuit 2, synchronized with the clock from the clock terminal 42,
memory 3, HiFi audio digital signal processing circuit 21,
It controls the D/A converter 23 and the digital output signal processing circuit 40.

In the embodiment configured as described above, the same clock as the PCM audio mode signal processing system is also used in the old F1 audio mode signal processing system. This makes the sampling frequencies of both signal systems the same. The digital output signal processing circuit 4° digitally processes and outputs both the PCM audio and the old F1 audio.

゛In this way, in this embodiment, unlike the conventional case, P
Like the commercial audio, the old F1 audio can also be output digitally.

Note that the present invention is not limited to the above embodiments,
For example, one head may serve as a PCM head and an old Fi head. In addition, although linear interpolation or smooth muting was used as a method for correcting noise, it is also possible to use sample hold, curve rectification, or replacement with PCM audio, or to switch the correction method depending on the length of the dropout. good. Further, although the above embodiment has been described as an example applied to a dropout correction device, it is obvious that the present invention can also be applied to a tape speed detection circuit, a double speed detection circuit, and the like.

[Effects of the Invention] As described above, according to the present invention, noise caused by dropouts and envelope omissions can be reliably corrected.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the noise correction device according to the present invention, FIG. 2 is a timing chart for explaining the operation of the embodiment, and FIGS. 3 and 6 are examples of the embodiment of FIG. 1. 4 is a block diagram showing a modified example of the VCA in FIG. 3.
5 is a timing chart for explaining the operation of the embodiment shown in FIG. 3, FIG. 7 is a block diagram showing another embodiment of the present invention, and FIGS. 9th
The figure is a block diagram showing a conventional noise correction device. 2... PCM digital signal processing circuit, 3... Memory, 12... A/D converter, 21... HiFi
Audio digital signal processing circuit, 22... Dropout detection circuit, 23... D/A converter. Figure 2 Figure 4

Claims (1)

[Scope of Claims] Reproducing means for reproducing information recorded on a recording medium capable of recording by digital and analog methods, and a memory, and the memory is used for a digital reproduction signal from the reproducing means. digital signal processing means for performing predetermined digital signal processing and outputting the signal; an A/D converter for converting the analog playback signal from the playback means into a digital signal; and an A/D converter for converting the analog playback signal from the playback means into a digital signal; a detection means for detecting and outputting a detection signal; and delaying the reproduction signal by transferring the reproduction signal from the A/D converter to the memory, and outputting the delayed reproduction signal from the memory at a timing based on the detection signal. A noise correction device comprising: a correction means for correcting and outputting a dropout portion of the noise correction means; and a D/A converter for converting the output of the correction means into an analog signal.