KR940000983B1 - Error noise signal reducing circuit for hi-fi audio signal - Google Patents

Abstract

The apparatus for reducing noise of HIFI audio signal in time base comprises an amplifier for amplifying the audio signal which two audio heads read on the video tape, two bandpass filters for filtering the signals for right and left channels from the amplified signals, an FM demodulator for demodulating the filtered signals, a memory for storing the demodulated signals, a controller for controlling the output of audio signal according to the detected phase of demodulated signals, a switch for switching the demodulated signals by switching signals, and a D/A converter for converting the output of the switch to digital signal. Thus this invention obtains the good sound by reducing the noise in time base.

Description

Time-base error noise signal reduction circuit of hi-fi audio signal

1 is a circuit diagram showing a conventional hi-fi audio signal reproducing system.

2 is a waveform diagram illustrating a timebase error noise signal generated in a conventional hi-fi audio signal reproducing system.

3 is a circuit diagram showing a hi-fi audio signal reproducing system configured with a timebase error noise signal reduction circuit of the present invention.

4 is a diagram for explaining detection of a timebase error in the present invention.

* Explanation of symbols for main parts of the drawings

21,22: Amplifier 23,24: L-Channel Bandpass Filter

25,26: R-channel bandpass filter 27-30: FM demodulator

31-34: Memory 35: Controller

36,37: Analog Switch 38,39: Digital-to-Analog Converter

AHD21, AHD22: First and second voice head SWP21: Switching signal

The present invention provides a video cassette recorder comprising: two audio heads provided separately from a video head in a head drum to generate time due to a phase difference of a reproduced audio signal when a stereo audio signal of an L channel and an R channel recorded on a video tape is reproduced. Time base error of hi-fi audio signal to reduce noise signal of time base error. The present invention relates to a noise signal reduction circuit. In particular, a time base error is stored in memory in addition to storing the reproduced FM demodulated L and R channel audio signals in a memory. The present invention relates to a timebase error noise signal reduction circuit of a hi-fi audio signal that detects an error and controls the output of the memory according to the detected timebase error so that there is no phase difference of the audio signal, thereby reducing the noise signal caused by the timebase error.

In general, in accordance with the trend of high-end video cassette recorders, stereo audio signals of L and R channels are converted into digital signals, modulated with carrier frequencies of 1.3 MHz and 1.7 MHz, and two headphone drums are installed separately from the video head. It is applied to the audio head, recorded, reproduced, and seeks Hi-Fi of the audio signal.

The conventional voice signal for reproducing such a hi-fi voice signal includes an amplifier (1) (2) for amplifying the voice signal reproduced by the first and second voice heads (AHD1) (AHD2) as shown in FIG. L-channel bandpass filters (3,4) and R-channel bandpass filters (5,6) for separating the L-channel and R-channel audio signals of 1.3 MHz and 1.7 MHz from the output signal of the amplifier (1) (2) ), An FM demodulator (7-10) for FM demodulating the output signal of the band pass filter (3-6), and the FM demodulator (7, 8) (9, 10), which are switched according to a switching signal (SWP1). An analog switch (11) (12) for selectively outputting the output signal of " " and a digital / analog converter (13) (14) for converting the output signal of the analog switch (11) (12) into an analog signal.

In the conventional hi-fi audio signal reproduction system configured as described above, when the video tape is played back, the first and second audio heads AHD1 and AHD2 play back the audio signal while alternately tracing the video tape at an angle of about 180 °. The reproduced audio signal is amplified by about 50-60 dB by the amplifier (1) (2) and output.

In the audio signal output from the amplifier (1) (2), the L-channel audio signal of 1.3 MHz is filtered out by the L-channel band pass filter (3) (4), respectively, and the 1.7-channel R-channel audio signal is output from the R channel band. The L and R channel audio signals output from the L and R channel band pass filters (3, 4) (5, 6) are respectively filtered and output from the pass filter (5) and (6). 8) FM demodulated at (9, 10) and output as a digital signal.

Then, the analog switches 11 and 12 are switched according to the switching signal SWP1 to select the output signals of the FM demodulators 7 and 8 and 9 and 10, so that the FM demodulators 7 and 8 and 9 and 10 The audio signals output intermittently alternately are continuously connected, and the output signals of the analog switches 11 and 12 are converted into analog signals by the digital / analog converters 13 and 14 to L and R channel audio signals. Output

In such a video cassette recorder, audio is recorded by intermittently recording audio signals to two audio heads at the time of recording the audio signal, and intermittently recording the audio signals to be intermittently reproduced. When recording signals, the audio signals reproduced by the two audio heads as shown in FIG. 2 are displayed due to the displacement due to the elasticity of the video tape and the error of the installation position of the two audio heads. There is no match, and a slight phase difference occurs.

However, the conventional voice signal reproducing system as described above continuously outputs intermittent voice signals regardless of the phase difference between the voice signals reproduced by the two voice heads. Due to the smoothness, a timebase error noise signal is generated, thereby degrading sound quality and causing discomfort to the user.

The present invention has been made to solve the above-mentioned problems, and the FM demodulator stores the FM demodulated voice signal in a memory, detects the phase difference of the FM demodulated voice signal, and stores the memory according to the detected phase difference. To provide a timebase error noise signal reduction circuit for reducing the noise signal of the time base error by controlling the phase difference of the audio signal to be matched with reference to the drawings of FIG. 3 and FIG. It explains in detail.

3 is a circuit diagram showing a hi-fi audio signal reproducing system in which the timebase error noise signal reduction circuit of the present invention is configured, and as shown therein, amplifies the audio signal reproduced by the first and second audio heads AHD21 and AHD22. L channel bandpass filters 23 and 24 and R for separating audio signals of L and R channels of 1.3 MHz and 1.7 MHz from the output signals of the amplifiers 21 and 22. And a channel demodulating filter (25, 26), an FM demodulator (27-30) for FM demodulating the output signal of the band pass filter (23-26), and an output signal of the FM demodulator (27-30). The controller 35 which detects the phase difference between the output memory 31-34 and the output signals of the FM demodulators 27 and 28 and controls the memory 31-34 to output an audio signal according to the detected phase difference. ) And an analog switch for selectively outputting the output signals of the FM demodulators 27, 28 (29, 30) by switching according to the switching signal SW21. It was composed of values (36,37), and a D / A converter 38, 39 for converting the output signal of the analog switch 36 (37) into an analog signal.

According to the present invention configured as described above, when the video tape is reproduced, the first and second audio heads AHD21 and AHD22 reproduce audio signals on the video tape, and the reproduced audio signals are amplified by the amplifiers 21 and 22, respectively. The L-channel bandpass filters 23 and 24 and the R-channel bandpass filters 25 and 26 are separated into L-channel and R-channel audio signals, and are then demodulated by the FM demodulator 27-30, respectively. 34 are entered and stored respectively.

The L channel audio signals respectively output from the FM demodulators 27 and 28 are input to the controller 35 to detect a phase difference.

That is, as shown in FIG. 4, when the phase difference of the audio signal reproduced by the first and second audio heads AHD21 (AHD22) is Δt at time tN, the audio heads AHD21 (AHD22) at time tN. The level difference ΔY of the audio signal reproduced by

ΔY = Ya (tN) -Yb (tN-1)

Here, Ya (tN) and Yb (tN-1) are digital demodulated L-channel audio signals reproduced by the first and second audio heads AHD21 and AHD22 at the time tN and tN-1, respectively. Value.

Becomes

The amount of change Ys of the digital value obtained by FM demodulation of the audio signal reproduced by the first audio head AHD21 during the sampling time ts is

Ya = Ya (tN) -Ya (tN-1)

Here, Ya (tN-1) is a digital value obtained by FM demodulating the L channel audio signal reproduced at the time tN-1 by the first audio head AHD21.

Becomes

Therefore, the phase difference Δt of the audio signals reproduced by the first and second audio heads AHD21 and AHD22 is

Δt = ts · (△ Y / Ys)

Becomes

According to the phase difference Δt calculated as described above, the controller 35 controls the audio signal output of the memory 31, 32, 33, 34 to output the L channel audio signal and the memory 33, which the memory 31, 32 outputs. There is no phase difference of the R channel audio signal outputted by 34).

In this way, the L and R channel voice signals output from the memories 31 and 32 (33 and 34) are continuously connected while the analog switches 36 and 37 are switched according to the switching signal SW21, and the analog switches 36 The output signal of, 37 is converted into an analog signal by the digital-to-analog converters 38 and 39 and output.

On the other hand, the above has been described taking an example of controlling the output of the memory (31-34) by detecting the phase difference of the L-channel audio signal output from the FM demodulator (37, 38), the FM demodulator (29) It is also possible to control the output of the memory 31-34 by detecting the phase difference of the R-channel audio signal outputted by the < RTI ID = 0.0 > 30, < / RTI > and the L-channel and R-channel audio output by the FM demodulators 27, 28, 29, 30. The phase difference of the signals can be detected to control the output of the memories 31 and 32 and 33 and 34 respectively.

As described in detail above, the present invention stores the FM demodulated voice signal in a memory in the FM demodulator, detects the phase difference of the FM demodulated voice signal, and controls the memory according to the detected phase difference to match the phase difference of the voice signal. By reducing the noise signal of timebase error, the sound quality is improved and the user's discomfort can be eliminated.

Claims (3)

Amplifiers 21 and 22 for amplifying the audio signals reproduced by the first and second audio heads AHD21 and AHD22, and L channels of 1.3 MHz and 1.7 MHz in the output signals of the amplifiers 21 and 22; L channel band pass filters 23 and 24 and R channel band pass filters 25 and 26 for separating audio signals of the R channel, and an FM demodulator for FM demodulating the output signals of the band pass filters 23 to 26. 27-30), the memory 31-34 for storing and outputting the output signal of the FM demodulator 27-30, and the phase difference between the output signals of the FM demodulators 27, 28 and detecting the phase difference. The controller 35 controls the memory 31-34 to output an audio signal, and is switched according to the switching signal SW21 to select the output signals of the FM demodulators 27, 28, 29, 30. An analog switch (36,37) for outputting, and a digital to analog converter (38) (39) for converting the output signal of the analog switch (36,37) to an analog signal. Is a timebase error noise signal reduction circuit of a hi-fi audio signal. The timebase error noise signal of the hi-fi audio signal according to claim 1, characterized in that the controller (35) controls the output of the audio signal of the memory (31-34) with the phase difference between the output signals of the FM demodulators (29, 30). Reduction circuit. 3. The controller (35) according to claim 1, characterized in that the controller (35) controls the audio signal output of the memories (31, 32) (33, 34) with the phase difference of the output signals of the FM demodulators (27, 28) (29, 30). A timebase error noise signal reduction circuit for a hi-fi audio signal.