JPH027267A - Noise reduction device - Google Patents

Abstract

PURPOSE:To generate a signal almost equivalent to a recorded voice signal and to reduce a head switching noise by reducing the noise by connecting the start point and the end point of the head switching noise by a linear interpolation circuit. CONSTITUTION:The carrier frequency of a frequency modulated voice signal receiving band limitation by a band-pass filter 5 is compared with the carrier frequency at the time of frequency-modulating the voice signal at a carrier frequency comparator 8, and a pulse is generated first by a hold pulse generation circuit 9 when the deviation of two carrier frequencies is generated. The start point of the head switching noise is judged by the pulse, and the end point of the head switching noise is judged by the pulse outputted when the deviation of the two carrier frequencies is restored to an original state. Meanwhile, the voice signal demodulated at a frequency demodulation circuit 7 is delayed at a demodulation signal delay circuit 10 so as to fit the timing of interpolation. Here, the voice signals at the time of the start point and the end point of the head switching noise are connected by the linear interpolation circuit 11. In such a way, it is possible to reduce the noise remarkably.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a noise reduction device used in a rotary head type magnetic recording and reproducing device having a function of recording and reproducing frequency modulated audio signals.

Conventional technology In recent years, magnetic recording has been developed to record frequency-modulated audio signals in a frequency band between the frequency-modulated luminance signal and the reduced-converted chromaticity signal in order to make the audio recorded on magnetic tapes used for video recording high-fidelity. A playback device has been put into practical use.

FIG. 3 is a schematic block diagram showing a head switching noise reduction device for frequency modulated audio signals in Hi-Fi VTH. In FIG. 3, 1 is a magnetic head for extracting frequency modulated audio signals from a magnetic tape. The frequency modulated audio signal extracted by the magnetic head is input to a preamplifier circuit 4 via a rotary transformer 2 and an audio head changeover switch 3 which is switched by an audio head switching pulse. The frequency modulated audio signal is amplified by the preamplifier circuit 4 to a level K that can sufficiently drive the circuits in the subsequent stages, subjected to band restriction by the band pass filter 5, and input to the frequency demodulation circuit 6, where it is frequency demodulated. The reception becomes an audio signal.

However, since one frequency modulated sound weight signal is extracted by two audio heads, and the audio head is selected by the audio head selector switch 3, it is made into one frequency modulated audio signal.
In the frequency modulated audio signal input to the preamplifier circuit 4, there is a portion where the carrier frequency is not properly connected, albeit for a short time, at the portion where the audio head is switched. In this part, the carrier frequency partially deviates greatly, and when the frequency is demodulated, the audio signal has a disturbance in the audio waveform at the timing of switching the audio head, as shown in the waveform at point F in Figure 4A. This results in noise.

Therefore, in order to reduce this noise, the audio head switching pulse that causes this noise is used, and the hold pulse generation circuit 7 outputs a pulse for the time that the noise occurs. The value hold circuit 8 maintains the level of the audio signal immediately before the occurrence of audio signal disturbance (noise) for the output time of the hold pulse, that is, the noise time, and reduces the energy of the noise and outputs it as an audio signal (Figure 4). Waveform of 1 point in 2). In the manner described above, the noise of the audio signal is reduced.

Problems to be Solved by the Invention In the noise reduction device configured as described above, noise reduction is achieved by simply maintaining the level of the audio signal immediately before the noise occurs, so it is possible to achieve a large noise reduction. The problem was that it was not possible.

Means for Solving the Problems In order to solve the above problems, the noise reduction device of the present invention includes a carrier frequency comparison circuit that compares the carrier frequency during modulation with the carrier frequency of a frequency-modulated audio signal subjected to band restriction during reproduction. , a hold pulse generation circuit that outputs a pulse when a shift occurs in the carrier frequency compared by this carrier frequency comparison circuit and when the shift returns to the original, and a hold pulse generation circuit that linearly interpolates the audio signal at the timing of the above pulse. It has a linear interpolation circuit and is configured to linearly interpolate the start and end points of head switching noise to reduce the noise.

Effect of the Invention With the above-described configuration, the present invention has the starting point of the head switching noise determined by the pulse generated when the two carrier frequencies being compared deviate, and the pulse generated when the deviation of the two carrier frequencies returns to the original value. Since the end point of the head switching noise determined by is connected with a straight line by a linear interpolation circuit to reduce the noise, a signal almost equivalent to the recorded audio signal is reproduced, which significantly reduces head switching noise. be able to.

Example Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is a schematic block diagram showing one embodiment of the present invention. In FIG. 1, a frequency modulated audio signal extracted from a magnetic tape by a magnetic head 1 is input to a preamplifier circuit 4 via a rotary transformer 2 and an audio head changeover switch 3 which is switched by an audio head switching pulse. The preamplifier circuit 4 amplifies the frequency modulated audio signal to a level that is sufficient to drive the circuits in the subsequent stages.The frequency modulated audio signal is then band-limited by the bandpass filter 6 and input to the frequency demodulation circuit 7 via the RF limiter 6. The frequency demodulated signal becomes an audio signal.

However, since the frequency modulated audio signal is extracted by two audio heads and the audio head is selected using the audio head selector switch to form one frequency modulated audio signal, the frequency modulated audio signal input to the preamplifier circuit 4 When the audio head is switched, the carrier frequency appears to be partially shifted for a short period of time, and when the frequency is demodulated, the audio signal has a difference in the timing shown in Figure 2 when the audio head is switched. As shown in the waveform at point D, the audio signal is disturbed and becomes noise.

Therefore, in order to reduce this noise, a carrier frequency comparison circuit 8 compares the carrier frequency of the frequency-modulated audio signal whose band has been limited by the band-pass filter 5 and the carrier frequency when the audio signal is frequency-modulated. , a hold pulse generating circuit 9 first generates a pulse when two carrier frequencies deviate. This pulse determines that it is the starting point of the head switching noise, and the pulse that is output when the two carrier frequencies return to the original determines that it is the end point of the head switching noise. do.

On the other hand, the audio signal demodulated by the frequency demodulation circuit 7 is delayed by the demodulation signal delay circuit 1o so as to match the timing of interpolation. The audio signal at this time and the end point are connected with a straight line, and the noise energy is significantly reduced and output as an audio signal (waveform at point E in Figure 2).

Effects of the Invention As is clear from the above embodiments, the present invention has advantages in that the starting point of head switching noise is determined by the pulse generated when the two carrier frequencies being compared are shifted, and the starting point is determined by the pulse generated when the two carrier frequencies are shifted. A linear interpolation circuit connects the end point of the head switching noise, which is determined by the pulse generated when the head switches back to Switching noise can be significantly reduced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the noise reduction device of the present invention, FIG. 2 is a waveform diagram of the audio signal at each point in FIG. 1,
FIG. 3 is a block diagram showing a conventional noise reduction device, and FIG. 4 is a waveform diagram of an audio signal at each point in FIG. 1...Audio magnetic head, 2...Rotary transformer, 3...Audio head switching switch, switch, 4...Preamplifier circuit, 5... ...Band pass filter, 6...RF limiter, 7...
... Frequency demodulation circuit, 8 ... Carrier frequency comparison circuit, 9 ... Hold pulse generation circuit,
1o...Audio signal delay circuit, 11...
Linear interpolation circuit. Name of agent: Patent attorney Toshio Nakao and one other person

Claims (1)

[Claims] A preamplifier circuit that amplifies the audio signal extracted from the magnetic tape by the rotating head, a bandpass filter that limits the band of the audio signal amplified by the preamplifier circuit and separates it into two types of carrier components, and a frequency An RF limiter that limits the level of the modulated audio signal, a frequency demodulation circuit that demodulates the frequency of the frequency modulated audio signal whose level has been limited by the RF limiter, and a frequency demodulation circuit that demodulates the frequency of the frequency modulated audio signal whose level has been limited by the RF limiter, and the frequency after being divided into two types of carrier components due to the band limit. A carrier frequency comparison circuit that compares the carrier frequency of a modulated audio signal and the carrier frequency when the audio signal is frequency modulated, and when a deviation occurs between the two carrier frequencies compared by this carrier frequency comparison circuit. and a hold pulse generation circuit that generates a pulse when the deviation returns to the original, a delay circuit that delays the demodulated audio signal and adjusts the interpolation timing, and a hold pulse generation circuit that generates a pulse on the delayed audio signal. and a linear interpolation circuit that linearly interpolates the audio signal at the time when a pulse occurs when a deviation occurs in the carrier frequencies compared with the audio signal at the time when a pulse occurs when the deviation returns to the original. A noise reduction device characterized by: