JPS60119668A - Sound magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To obtain a reproduced sound excellent in quality by sampling and holding a sound signal with a sampling pulse in synchronizing with a head switching pulse, and having a larger period than noise generating period so as to suppress the switching noise. CONSTITUTION:An oscillating signal of a reference oscillator 28 is frequency-divided by a frequency divider 29 to form a sampling pulse fc. The sampling clock fc is inputted to a clock input of a D type flip-flop 30 and a head switching pulse (f) is inputted to the data input to form a head switching pulse f' in synchronizing with the sampling pulse fc at the output Q. An output (a) of a demodulator 19 is sampled and held by using the sampling pulse fc at a sample-and- hold circuit 31, an output (d) is eliminated for the sampling pulse fc through a filter 32 and a de-emphasis circuit 101 to obtain a sound signal S2.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an FM audio magnetic recording and reproducing device that performs FM modulation on an audio signal and records the audio signal on a magnetic tape using a rotating head, and is mainly used for home use. Suitable for use in VTRs.

[Background of the invention]

Conventionally, in a home VTR (VH8 system, for example), audio signals are recorded using a fixed head on an audio trunk 2 provided separately from a video trunk 1 on a magnetic tape 6, as shown in FIG. In this case, because the tape speed is slow (for example, in 6x mode of VH8, N'rSC system,
1 Ryu/S), sufficient dynamic range, and frequency characteristics cannot be obtained. As a means to solve this problem, it has been proposed to frequency-multiplex the audio signal 6 between the frequency bands of the FM luminance signal 4 and the low frequency converted chroma signal 5, as shown in FIG.

FIG. 3 shows a specific head configuration of a magnetic recording/reproducing apparatus for recording such audio signals on a magnetic tape. Audio signals are recorded diagonally with respect to the longitudinal direction.

FIG. 4 shows an example of the circuit configuration of a recording and reproducing circuit of a conventional magnetic recording and reproducing apparatus.As shown in FIG. 4(a), the audio signal S is sent to a pre-emphasis circuit 1o.

After passing through the FM modulator 10, the signal becomes an F'M audio signal. On the other hand, the video signal V is converted into an FM luminance signal and a low-frequency-converted p-ma signal by the recording video signal processing circuit 11, and is supplied to the adder 12. After the adder 12 adds the audio signal and the video signal, it is supplied to the recording amplifier 13, amplified by the recording amplifier 15, and recorded on the tape s by the head 8.9. Further, as shown in FIG. 4(b), the signal on the tape 3 is reproduced by the head 8.9, and the output of the head 8 is reproduced by the preamplifier 14.9. After each output of the head 9 is amplified by a preamplifier 15, the output is switched by a switch 16 controlled by a head switching pulse f. Of the outputs of the switch 16, the FM luminance signal and the low-frequency conversion chroma signal pass through the reproduced video signal processing circuit 17 and become the video signal V.The FM audio signal, on the other hand, is band-limited by the BPFla, demodulated by the demodulator 111619, and then digitalized. After passing through the emphasis circuit 101, it becomes the audio signal S.

FIG. 5 shows the FM audio signal S which is the head switching pulse f1 hect 8, the output of head 9, and the output of BPFla during playback.
FM shows the waveform of the audio signal S that has passed through the post-demodulation de-emphasis circuit 101. The head switching pulse f is 50 Hz in the NTSC system and 25 h in the PAL system. In the following explanation, the case of the NTSC system will be described. The PM audio signal SFM is output from the output 20. of the hector 8 as shown in FIG. Since the phase of the FM audio signal is discontinuous in the switching section 22, which is configured by switching the output 21 of the head 9 using the head switching pulse f,
Noise 25 occurs in the demodulated signal S. In order to remove this noise 23, conventionally, as shown in FIG. 6, a gate pulse g is generated from the head switching pulse f by a gate circuit 24, and the output a of the demodulator 19 is held by a hold circuit 25 only during the gate period. The waveform of the hold circuit output is improved by a de-emphasis circuit 101 to obtain an audio output Sl.

FIG. 7 shows waveforms of various parts of the circuit shown in FIG. 6. Although the noise 23 is removed by hold and de-emphasis, the waveform distortion 26 synchronized with the head switching pulse f remains in the audio output S1.
60Hz and its harmonic noise (hereinafter referred to as switching noise) cannot be completely removed. This effect is particularly noticeable in the case of single-frequency signals. As shown in FIG. 8, the cutoff frequency is f as the de-emphasis characteristic 27. When the latter is used, assuming that the signal level is 0 and the switching noise is N, the C/N will deteriorate as a signal of f0 or higher passes through the de-emphasis circuit 101. That is, before the de-emphasis circuit 101, the ratio of C1/N was 0, but at the output of the de-emphasis circuit 101, the ratio becomes C,/N. this is,
The frequency of switching noise N is the cutoff frequency f0
This is because it is sufficiently low and is not affected by the attenuation characteristics of the de-emphasis circuit 101, and the switching noise level is constant before and after the de-emphasis circuit 101. Therefore, for signals with frequencies higher than the cutoff frequency of 10, the degree of C/N deterioration is 6 dB1 relative to the frequency.
1, which increases at 0 Ct. Therefore, the higher the signal frequency, the more the sound quality deteriorates, which is an extremely serious problem in practice.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic audio recording and reproducing apparatus which suppresses the above-mentioned switching noise and obtains good reproduced sound quality.

[Summary of the invention]

The present invention creates a sampling pulse that is synchronized with the head switching pulse and whose period is larger than the noise generation period,
This is characterized in that the generation of switching noise is suppressed by sampling and holding the audio signal. [Embodiments of the Invention] Specific embodiments of the present invention will be described in detail below. 9th
The figure shows the circuit configuration of the present invention, where the recording system is the fourth
Since it is the same as the figure, only the reproduction system is shown. The differences from the conventional example shown in FIG. fa4 are as follows: (1) The frequency of the oscillation signal of the reference oscillator 2B is divided by the divider 29 to generate the sampling pulse fc.

(2) Hella) Using 7 rips from the switching pulse f and the flop circuit 50, generate a head switching pulse f' synchronized with the sampling pulse fc.

(3) The output a of the repeater 19 is sampled and held using the sample and hold circuit 31 and the sampling pulse fc, and the output d is sent to the filter 32. The component of the sampling pulse fc is removed by passing it through the de-emphasis circuit 101, and the audio signal S! get.

etc.

As the reference oscillator 28, 3 and 5 oscillators used in color systems are used.
If the W reference oscillator 28, which can be an 8 MHz crystal oscillator, is one that oscillates with the sampling pulse fc, the frequency divider 29 is not necessary. The filter 32 is an LPF or a filter.

A case will be described in which 3.588@2 crystals + 3 oscillators are used as the 6 or less reference oscillator 28 in which a trap for the combining pulse fc is used. The conditions for the sampling pulse fc include an audio frequency band (3 times or more of 20KFIθ).

- For example, T = 1/fc = 134 μs where f. = 5,579,545Hz. On the other hand, in the servo system, the rotational frequency fv of the drum during reproduction is selected as follows. fv coincides with the frequency of the head switching pulse f, and as described above, the sampling pulse fc
If you select , an integer number of sampling pulses, 2488 (= 119,
424/4B).

The operation of the present invention will be explained using FIG.

The first point of the present invention is to make the timing of the rise and fall of the head switching pulse (this coincides with the switching point of the two heads 8.9) coincide with the sampling pulse fc. Generally, the head switching pulse f has a form in which the rise and fall timings can be adjusted in order to absorb variations in mechanical accuracy of the heads 8.9 on the rotating drum 7 shown in FIG. Adjustment accuracy is approximately ±IH (
IH=63.5 μs), and within this range, the outputs 20.21 of the two heads 8 and 9 are connected without a gap. However, since the phase discontinuity of the FM signal remains, noise 25 occurs immediately after the switching point 22 in the demodulated output a. The period of noise 23 is approximately 5-7 μs.

Therefore, the period T of the sampling pulse fc is T>7μ
s, and if the switching point 22 and the sampling pulse match, and after sampling, hold for a period of T, the noise 25
can be completely removed.

The second point of the present invention is that the demodulated audio signal is constantly sampled by the sampling pulse f. Since the sampling is performed at , the local waveform distortion 26 shown in FIG. 7 does not occur. Therefore, 5011z, 6 Hz and their harmonics, ie, switching noise, are not generated. The unnecessary spectrum includes the sampling pulse fc and its harmonics, and the crossbeat between the high-order distortion of the audio signal and the sampling pulse fc.

However, the former can be removed by trapping the LPF or sampling pulse fc, and the latter can be removed by trapping the sampling pulse fc.
This problem can be solved by giving sufficient consideration to the linearity design of the audio signal system.

The series of waveforms shown in FIG. 10 shows what has been described above, and from the sampling pulse fc obtained by dividing the reference frequency fsc and the head switching pulse f, a head switching pulse f/ synchronized with the sampling pulse fc is created. . head 8
Switching between the output 20 of the head and the output 20 of the head is performed by a head switching pulse f/. Since the switching point 22 and the sampling pulse fc coincide, the sample-and-hold signal has a form with the noise 23 removed, as shown in d of FIG. 10 (7). The sample and hold signal d is filtered 32.
By passing it through the de-emphasis circuit 101, the sampling pulse (near 4fQIz) is removed and an audio output S is obtained.

In addition, in order to create the head switching pulse f/ synchronized with the sampling pulse fc, the D type 7 is used as shown in FIG.
Lip 70 tube 3o is used. 7 as shown in Figure 11.
If a sampling pulse fc is inputted to the clock input CL of the printer flop 30 and a head switching pulse f is inputted to the data input, a head switching pulse f' is obtained at the output Q.

As shown in Fig. 12, when the audio signal is stereo and has an L channel 6a and an R channel 6b,
The recording system is a modulator 10a as shown in FIG.

IDb, pre-emphasis circuit 100a, 100b
will be established. The reproduction system is as shown in FIG. 14, with BPF 18a, 18b and demodulator 1 for the R channel.
9a, 19b, sample and hold circuits 31a, 51b
, filter 32a, +2b, de-emphasis circuit 1
01a and 101b may be provided. Further, as shown in FIG. 15, video heads 35 and 54 for recording and reproducing FM luminance signals and low-frequency conversion chroma signals, and heads dedicated to audio '6' 5.5
6, record the audio signal in the depth direction of the tape,
Some systems record video signals superficially. in this case,
As shown in FIG. 16, the recording system is provided with a recording amplifier 37 dedicated to the video system, and as shown in FIG. Reproduction signal processing circuit 1
Add to 7. Regarding head output switching, for example, a head switching pulse F for the video heads 55 and 34 may be created, and a switching pulse f for the audio heads 35 and 5 (S) may be created from the head switching pulse F using the monomulti 41. If the signal is stereo, see Figures 1'5 and 14.
As shown in the figure, two audio signal processing systems may be provided.

Furthermore, without using a video head, an audio-only head 35,
The present invention can be applied in exactly the same way to a system that records and reproduces only audio using a chroma subgear fsc. Any frequency may be used as long as it satisfies two conditions: 25 times the frequency or more and the period T is 7 μs or more.

Furthermore, the present invention can be applied in exactly the same way not only to the NTSC system but also to the PAL and SECAM systems by using a 4.43 MHz crystal as the reference oscillator 28 and changing the frequency division ratio of the frequency division M29.

〔Effect of the invention〕

As described above, in the present invention, switching between two head outputs is performed using a head switching pulse that is synchronized with a sampling pulse, and the audio signal is sampled and held using the sampling pulse, thereby reducing the switching noise that accompanies head output switching. This can significantly improve the sound quality of an audio recording/reproducing device using a rotary head.

[Brief explanation of drawings]

Figure 1 is a tape pattern diagram for audio recording in a conventional magnetic recording/reproducing device, Figure 2 is a spectrum diagram of a video/audio multiplexed signal,
Figure 3 is a head configuration diagram, Figure 4 is a block diagram of a conventional FM audio multiplexing circuit, Figure 5 is a waveform diagram of each part of the conventional circuit, and Figure 6 is a pull diagram of a conventional switching noise removal circuit. The figure is a waveform diagram of each part of FIG. 6, FIG. 8 is an explanatory diagram of deterioration caused by the de-emphasis circuit, FIG. 9 is a block diagram of the reproduction circuit of the audio magnetic recording and reproduction apparatus of the present invention, and FIG. Figure 9 is a signal waveform diagram of each part, Figure 11 is a block diagram of a flip-flop circuit that synchronizes head switching pulses and sampling pulses, 12th FA is a spectrum diagram of a stereo audio signal, and Figure 13 is a recording system for a stereo audio signal. Fig. 14 is a block diagram of the playback system, Fig. 15 is a plan view of the head configuration when an audio-only head is used once a month, and Fig. 16 is a block diagram of the recording circuit in the case of Fig. 15. , FIG. 17 is a block diagram of the reproducing circuit. 2nd... Reference oscillator, 29... Frequency divider, 31...
Sample/hold circuit, 32...filter. Fig. 1 2 Fig. 2 Fig. 3 Exit Fig. 4/1 Fig. 5 Fig. 6 Off Fig. 2 ivy fig. j) 6 ax 6 fig. noah g

Claims (1)

[Claims] In an audio magnetic recording and reproducing apparatus that records FM audio signals on a magnetic tape using a plurality of rotating heads, there is provided a sampling pulse generation means, a sample hold means for sample-holding a demodulated audio signal using the sampling pulse, and a sample hold means. means for removing the sampling frequency component from the output of the sampling pulse and F
An audio magnetic recording and reproducing device comprising means for matching the switching point of the M audio signal with the switching point of the audio signal.