JPS60182505A - Eliminating circuit for sound signal noise - Google Patents

Abstract

PURPOSE:To improve the waveform fidelity by giving PAM modulation to a high frequency carrier synchronous with an RF switching pulse with a reproduced sound signal and therefore eliminating the switching noise to avoid mixture of low band noises to the sound signal. CONSTITUTION:A hold mode period is set equal to or slightly larger than the time width of a switching noise as shown by a figure A. At the same time, a control signal E is synchronous with an RF switching pulse F. Therefore the PAM modulating action is equal to a preholding action at a track changeover time point. The noise width can be estimated by the band of a reproduced sound signal route and therefore decided easily. A reproduced sound signal A containing the switching noise due to the switching by the pulse F is sampled and held with the timing as shown by E. Thus a sampling/holding output is obtained as shown by B, and a PAM modulation output is obtained as shown by C. This signal C is interpolated by an LPF to obtain a sound signal free from the switching noise as shown by D.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to an audio signal noise removal circuit for a magnetic recording/reproducing device that performs FM modulation on an audio signal and records and reproduces the same using a plurality of rotating discs.

(b) Conventional technology In a magnetic recording and reproducing device that modulates an audio signal and records and reproduces it on a plurality of rotary heads, for example, a β-H1-I method video cheap recorder, when the reproduction track is switched during reproduction, the reproduction FM The audio signal becomes discontinuous and large amplitude noise occurs.

Therefore, in the past, the first method of
As shown in the figure, a method is used to maintain the signal level immediately before the noise occurs.

This method will be explained based on FIG. In the figure, (a
) is the continuous reproduction F produced by two rotating heads.
M audio signal, (b) is the FM demodulated audio signal, (C)
is a pre-hold instruction signal created based on an RF switching pulse which is a head switching signal created in relation to the rotational phase of the rotary head, and (d) is an audio signal from which noise has been removed by pre-hold.

As is clear from the figure, the large amplitude noise (9) has been removed, but the original signal is not faithfully rewritten, and the RF switching pulse 25Hz (PAL/SEC
AM) or a frequency signal related to 6σHz (N, TSC)) is superimposed, and this frequency signal is within the audible range and is emphasized by noise reduction during playback, so it is not unpleasant to the ear. there were.

(c) Purpose of the Invention The present invention has been made in view of the above points, and (c) Structure of the Invention The present invention provides an FMv-tuned audio signal to be recorded on a plurality of magnetic recording media using a plurality of rotating heads. In an audio signal noise removal circuit of a magnetic recording and reproducing device that reproduces an audio signal that has been FM modulated by a rotary head, the circuit includes: a means for creating a switching signal that corresponds to the rotational phase of the plurality of rotary heads; switching means for serializing the reproduced FM audio signals from the plurality of rotating heads; means for demodulating the serialized reproduced FM audio signals; and means for synchronizing the demodulated reproduced audio signals with the switching signal.
This is an audio signal noise removal circuit characterized by comprising means for performing PAM modulation based on a high frequency pulse outside the radio frequency band, and means for PAM demodulating the PAM-modulated reproduced audio signal.

(e) Examples An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a video tape recorder audio recording and reproducing circuit employing the present invention. The audio circuit has two left and right channels, but only the left channel will be explained below.

(1) is the audio input terminal, (2) is the first recording/playback switch, and (3) is the first low-pass filter (LPF).
, 14) is a noise reduction circuit, +51 is an amplifier,
(6) is an FM modulator, and the left and right carriers are different. 17) is a first band pass filter (BPF);
(9) is the FM modulated left and right audio signal (fL) (fR
) adder, IJO) is a recording amplifier. (Ill
is the second recording/playback switch, which switches the first and second switches during recording.
A recording signal is supplied to the rotary heads (HA) (HB) via a rotary transformer (not shown).

(The decoy is heated by a head motor that drives a rotating head, and
RF switching pulses (RF) related to the head rotational phase are obtained by known means.

During playback, the first and second recording/playback switches j21111)
has switched to the playback side, and the first and second rotating heads (mouth A
) (HB) The playback signal from the playback amplifier corresponding to each head! 14! It is supplied to the changeover switch (15) via ItJ. The changeover switch (15) is controlled by the above-mentioned RF switching pulse (RF), so that one output amplifier per field of the video signal (14) is output.
The first and second rotating heads (H
A) The reproduced signal from (HB) is made continuous.

Continuous playback by operation of selector switch f15+
= has different passband values, separates the left and right audio signals #,
It is separated by a band pass filter 6).

The left channel reproduced FM Makusei Tsukugo (fL) separated by the bandpass filter q0 is converted to FM through the limiter (1η).
The demodulator (18) performs FM demodulation, and the 20th bus filter f19 removes the FM modulation carrier. Note that the cutoff frequency of the 20jth bus filter 1ijJ) is set higher than that of the 10th pass filter (3). As described above, switching noise at the time of track switching is superimposed on the output of the streak 20-pass filter ttS. And this switching noise NJ IA
It is known that I is determined by the band of the 20-bass filter.

Conventionally, n
(Although J position holding means was provided, in the present invention, it is considered that a PAM (Pulse Amplitude Modulation) circuit (4)) is installed and outputs. The reference signal for PAMi modulation is created by a carrier creation circuit (2D) that is synchronized with the RF switching pulse (RF). The demodulated reproduced audio signal containing the switching noise is -HPAM modulated, and this signal is 60-bus filter 1, PAM demodulation is performed.

The PAM demodulated audio signal does not contain switching noise, as will be described later. This signal is output to the output terminal (3) via the first recording/reproducing switch (a), the Bi low-pass filter (3), and the noise reduction circuit (141) whose transfer characteristic has been changed to the opposite of that at the time of recording. Ru. FIG. 2 is a circuit block diagram showing the periphery of the PAM modulation circuit in more detail. (4) has a cutoff frequency of 1”1
This is an active/low bass filter of about OKH2 and corresponds to the LPF Ill. (Sl) is the first gate switch, 31) is the hold circuit, (Sl) is the second gate switch, and (32+ is the 60th bus filter with a cant-off of about 20 KHz for PAM demodulation. Hours are branch kakuntas. Inputs the tarokku No. 1d (CL) from a crystal oscillator of approximately 2 MHz and MH2, and the reset pulse (Re) synchronized with the rise and fall of the RF switching pulse (RF) is input to the reset terminal (R). .

Therefore, the carrier signal (Ca) from Kakunta (C) is R
It is synchronized with the rise and fall of the F switching pulse (see Figure 6). Further, the frequency of the carrier signal (Ca) is set to about 40 KHz or more according to the sampling theorem.

A signal (S) for controlling the first and second gate switches (Sl) based on the carrier signal (Ca) is created by, for example, a monomulti signal (b) triggered by a falling edge. This monomulti f34) may not be necessary in some cases. First and second gate switches (Sl) (Sl)
are controlled so that they are turned on and off at mutually complementary timing. That is, when the control signal (S) is at the low level, only the first gate switch (Sl) is on and the reproduced audio signal is supplied to the capacitor (CH). Also, when the level is NO, only the second gate switch (Sl) is on, and the analog value at the falling edge of the control signal is held, and only the held signal is shown in Figure 4, CG.
) can be obtained as follows.

By setting the above-mentioned hold mode period to be equal to or slightly thicker than the time width of the switching noise as shown in Figure 4, the control signal (E) can be synchronized with the RF switching pulse (). As a result, the PAM plexus adjustment operation at the time of trunk switching is the same as the pre-holding operation in Fig. 6.The width of the noise is as described above.
This can be easily realized because it can be predicted based on the band of the reproduced audio signal path. The reproduced audio signal (A) which has switching noise due to switching by the RF switching pulse region in FIG. 4 is sampled and held at the timing shown in (E), and the sampled and held output is as shown in (B). A PAM modulation output as shown in (C) is obtained. The relationship of frequencies to Tadahe is different from that of Minoru1na.

By interpolating this pulse signal (C) with a low-pass filter (32), a voice I= signal from which switching noise has been removed as shown in (D) is obtained.

As described above, by performing PAMR modulation of the high frequency carrier synchronized with the RF switching pulse with the reproduced audio signal, pre-maintenance against switching noise is performed, and 0T
Since the reproduced audio signal is sampled and bolded using a carrier signal other than the broadcast band, low-frequency noise as in the conventional example can no longer be heard.

In the above embodiment, synchronization with the carrier signal is achieved by resetting the frequency dividing circuit with an RF switching pulse, but a configuration in which a carrier synchronized with the RF switching pulse is created using a well-known PLL is also possible. RF
It is also possible to use two 'Cu pressure controlled oscillators driven start-stop based on switching pulses. Further, when a circuit as shown in FIG. 5 is used as the sample 4 rehold circuit, stability is further increased when the carrier signal is set to a high frequency.

(F) Effects of the Invention Since the configuration is as described above, the present invention eliminates low noise from the audio signal by removing switching noise, as in the prior art, and improves the fidelity of the waveform.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a circuit block diagram showing the specific configuration of the main parts, FIG. 6 is a waveform diagram showing the relationship between RF switching pulses and carrier signals, and FIG.
The figure is a waveform diagram showing the circuit operation of the embodiment, FIG. 5 is a circuit block diagram showing another embodiment of the sample and hold circuit, and FIG.
The figure is a waveform diagram for explaining the conventional method. Explanation of main symbols () (A) (HB)... Rotating head, f151...
Selector switch, 08)...FM demodulator, 119)...
・PAM modulator, (21)...carrier creation circuit, t
I! 21...PAM demodulator. Applicant Sanyo Electric Co., Ltd. Representative Patent Attorney Shizuo Sano Figure 8 Figure 6

Claims (1)

[Claims] (1) In an audio signal noise removal circuit of a magnetic recording and reproducing device that reproduces an FM-modulated audio signal using a plurality of rotary heads from a magnetic recording medium on which FM-modulated audio 4F$ is recorded using a plurality of rotary heads, means for creating a switching signal related to the rotational phase of the plurality of rotary heads; a switching means for serializing the reproduced FM audio signals from the plurality of rotary heads based on the switching signal; and the serialized reproduced FM audio. means for demodulating a signal; means for PAM-modulating the demodulated reproduced audio signal based on a high frequency pulse outside the audible band in synchronization with the switching number 48; and PAM demodulation of the PAM-modulated Nyu Shinsei ID code What is claimed is: 1. An audio signal noise removal circuit characterized by comprising means for: