JPS5911967B2 - playback device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION It has been considered to record and reproduce audio signals using a magnetic recording and reproducing device having a rotating magnetic head, similar to a VTR for recording and reproducing video signals.

FIG. 1 shows an example of the recording system, in which an audio signal (frequency band is, for example, 20Hz to 20KHz) is supplied from an input terminal 1 to an FM modulation circuit 4 through a preamplifier 2 and a preemphasis circuit 3, where it is converted into an FM signal. (For example, if the carrier frequency is 600kHz and the occupied band is ±400kHz
), and this FM signal is supplied through the recording amplifier 5 to, for example, two rotating magnetic heads 6A and 6B.

The heads 6A and 6B are constructed similarly to those of a VTR, that is, the heads 6A and 6B are mounted with an angular spacing of 1800 degrees from each other with respect to the rotating shaft 11, and are driven by a motor 12. For example, it is rotated at a rate of 30 times per second.

The magnetic tape 1 is placed obliquely over an angular range of over 1800 degrees with respect to the rotating circumferential surfaces of the heads 6A and 6B, and
It is made to run at a constant speed. Therefore, the FM signals supplied to the heads 6A and 6B are sequentially recorded as one diagonal magnetic track on the tape □ for a little over 1/60 seconds. Further, at this time, for example, two pulse generating means 13A and 13B are provided for the rotating shaft 11, and these generating means 13
Pulses are taken out from A and 13B alternately every half rotation of the heads 6A and 6B, and these pulses are supplied to the mixing circuit 15 through pulse amplifiers 14A and 14B, and are converted into pulses every half rotation of the heads 6A and 6B. , this pulse is supplied to the magnetic head 11 through the recording amplifier 16,
This pulse is recorded on the edge of the tape 1 as a magnetic track along its length. On the other hand, FIG. 2 shows an example of the reproduction system, in which the heads 6A and 6B are connected to the motor 1.
2 allows it to rotate at the same speed as when recording. A pulse of 00 is taken out from the mixing circuit 15 every half rotation of the heads 6A and 6B, and this pulse is sent to the phase comparator circuit 18.
At the same time, the head 11 reproduces the pulses recorded on the edge of the tape □, and the reproduced pulses are supplied to the comparison circuit 18 through the reproduction amplifier 19, and the mixing circuit 15 pulse from and amplifier 1
The phase of the pulse from 9 is compared. This phase comparison output is then supplied to the motor 12 to control the rotational phases of the heads 6A, 6B so that the heads 6A, 6B can correctly scan the magnetic track of the FM signal on the tape 7.

Therefore, FM signals are alternately reproduced from the heads 6A and 6B every half rotation of the heads 6A and 6B, and these reproduced FM signals are supplied to the switch circuit 22 through the reproduction amplifiers 21A and 21B, and Amplifier 14A, 1
4B, pulses are taken out alternately every half rotation of the heads 6A, 6B, and these pulses are supplied to the switching signal forming circuit 20 to form a rectangular wave signal that is inverted every half rotation of the heads 6A, 6B. This rectangular wave signal is supplied to the switch circuit 22 as its control signal.

Therefore, the FM signals reproduced by the heads 6A and 6B are continuously taken out from the switch circuit 22. The FM signal from this switch circuit 22 is transmitted to the limiter 23.
The demodulated audio signal is supplied to the FM demodulation circuit 24 through the FM demodulation circuit 24 to demodulate the original audio signal, and the demodulated audio signal is supplied to the low-pass filter 25 to remove the carrier component. It is taken out.

In this case, since the audio signal is recorded and reproduced in the form of an FM signal with a high carrier frequency, various characteristics such as S/N, dynamic range, frequency characteristics, and distortion characteristics can be made excellent.

Furthermore, since recording and reproduction are performed using a rotating head, the recording density can be increased and recording and reproduction can be performed for a long time.
However, in such a rotary head type device, if there is a skew or the like, switching noise will be included in the demodulated audio signal when the switch circuit 22 is switched.

In other words, for the sake of simplicity, if we consider the FM signal in an unmodulated state (no audio signal), if there is no skew,
The FM signal from the switch circuit 22 has a continuous waveform even at Ta and tb when the switch circuit 22 is switched, as shown in FIG. 3A.

However, if there is a skew, the FM signal from the switch circuit 22 will be transmitted to the switch circuit 22 as shown in FIG. 3B.
When switching, Ta and tb become discontinuous. In this way, when the FM signal is discontinuous, its phase changes rapidly as shown in Figure 3C, but demodulating the FM signal means is to differentiate the waveform of .

Therefore, when the FM signal (7) in Fig. 3B is demodulated, the waveform of the demodulated signal (audio signal) becomes a differential waveform of the waveform in Fig. 3C, as shown in Fig. 3D, that is, , the demodulated signal includes pulse-like switching noise S caused by switching Ta and tb of the switch circuit 22.
d is included. In such a case, generally, a gate circuit and a hold circuit are provided in the audio signal path after the demodulation circuit 24, and the period of the switching noise Sd,
In addition to blocking the audio signal path and removing the switching noise Sd, since the original audio signal is missing at this time,
During this absence period, the level of the audio signal is held at the previous level.

However, in this method, since the deleted audio signal is corrected by holding it at the level immediately before it, distortion inevitably occurs in the waveform, and the high-fidelity recording and reproduction becomes meaningless. In view of these points, the present invention attempts to prevent switching noise from being included without impairing the characteristics of the demodulated signal.

By the way, in the above-mentioned recording and reproducing apparatus, the tape 7 is run over an 18" angle range of the rotational surface of the heads 6A, 6B, so in the range exceeding 1800, the tape 7 runs on the rotating surface of the heads 6A, 6B. are both brought into contact with the tape 7 at the same time. Therefore, the audio signal during this period is 2
The output signals taken out alternately from the heads 6A and 6B when these are reproduced are shown in FIG. 4A. As shown at B, there is an overlapping period Ta at both ends of each magnetic track, during which the same signal is simultaneously taken out from both heads 6A and 6B. Conventionally, switching of the switch circuit 22 was performed at any time during the period Ta during which these signals were simultaneously taken out. The present invention focuses on this point,
1, the input switching noise Sd is removed by sampling the FM demodulated audio signal at a frequency higher than the audible frequency and switching the switch circuit 22 during the period when this sampling is not performed. be.

An example of this will be explained below. In FIG. 5, as explained in FIG. 3 and as shown in FIG. 4C, an audio signal including switching noise Sd is extracted from the low-pass filter 25. The signal is supplied to the sampling gate circuit 31.

Further, as shown in FIG. 4D, the oscillator circuit 32 outputs a crotter pulse having a frequency sufficiently higher than the audible frequency, for example, 60 kHz.

This clock pulse is supplied as a control signal to the gate circuit 31 through the pulse amplifier 33, and when this clock pulse is at a high potential, the gate circuit 31 becomes conductive and sampling is performed. Therefore, a sampled audio signal is taken out from the gate circuit 31 as shown in FIG. 4E.

1, this signal is supplied to a low-pass filter 34 for demodulation to demodulate the original audio signal, and this demodulated signal passes through a de-emphasis circuit 26 and an amplifier 27 to a terminal 2.
It is taken out at 8.

On the other hand, the switching signal forming circuit 20 has two RSs, for example.
It is composed of a flip-flop circuit, whose Q output and Q output are supplied to the J and K terminals of a JK flip-flop circuit 35, and the above-mentioned clock pulse is supplied to the clock terminal of this flip-flop circuit 35.

Therefore, a rectangular wave signal whose rising and falling phases of C are synchronized with the falling phase of the clock pulse is taken out from the flip-flop circuit 35 as shown in FIG. 4F, and this signal is sent to the switch circuit 22. Supplied as a control signal. According to this, the clock pulse is at a low potential at the switching times ta' and Tb' of the switch circuit 22.

Therefore, at these times Ta' and Tb', sampling is not performed in the gate circuit 31 and the switching noise Sd is not sampled, so that the demodulated signal taken out to the output terminal 28 does not include the switching noise Sd. In this way, it is possible to reproduce an audio signal without switching noise Sd. In this case, according to the present invention lζ, the FM
The demodulated audio signal is further sampled, and this sampled signal is demodulated to extract the output signal.In addition, the switch circuit 22 is switched during the period when this sampling is not performed, so that the audio No signal distortion occurs.

Furthermore, since the circular wave number of sampling is set sufficiently higher than the audible frequency, the sampling does not cause distortion in the audio signal.

Note that if the input signal is an FM signal, and this FM signal is recorded on a magnetic sheet as a separate track for each unit period, and continuous playback is performed by switching the playback output of the track, this is not applicable. The invention can be applied.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of an example of a recording device, Fig. 2 is a system diagram of an example of a reproducing device, Fig. 3 is a waveform diagram for explanation, and Fig. 4 is a system diagram of an example of a reproducing device.
The figure is a waveform diagram for explaining the present invention, and FIG. 5 is a system diagram of an example of the present invention. 22 is a switch circuit, 31 is a sampling gate circuit,
32 is an oscillation circuit, and 34 is a low-pass filter.

Claims (1)

[Claims] 1. An input signal is modulated, and this modulated signal is recorded in a different track for each unit period. The tracks are sequentially switched and scanned, and the modulated signal is continuously taken out to reproduce the input signal. In the reproducing device, a first demodulation circuit that demodulates the extracted modulated signal;
a sampling circuit that samples the demodulated signal of the first demodulation circuit at a frequency sufficiently higher than the maximum frequency of the input signal; a second demodulation circuit that demodulates the sampled signal; and a switch circuit that switches the tracks. and a reproducing apparatus which switches the tracks during a period in which the sampling is not performed so that switching noise caused by the switching is not included in the input signal that is reproduced.