JP3138044B2 - Audio signal processing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio signal processing apparatus at the time of special reproduction (particularly, at double speed reproduction) such as a HIFI-VTR (video tape recorder).

[0002]

2. Description of the Related Art Hitherto, as this kind of HIFI audio signal processing apparatus, for example, Japanese Patent Laid-Open Publication No. Sho 60-107
No. 984 (H04N 5/91). In this publication, a continuous reproduced audio signal is obtained by switching a reproduced audio signal from an audio head by a switch circuit at a standard tape speed. In that case, in order to prevent deterioration of sound quality due to switching noise generated at the time of switching of the switch circuit, the band of the band variable filter circuit connected to the output of the sample and hold circuit is
It is proposed that the bandwidth during the sample hold period be narrower than the bandwidth during the other periods.

[0003] By the way, when a tape on which HIFI audio is recorded is specially reproduced, for example, at a double speed, a noise bar is fixed in the video signal, and a reproduction screen that can endure viewing can be obtained. Since the HIFI audio signal is reproduced by obliquely tracing the adjacent track, out-of-band noise and buzz sound are generated, and the reproduced sound at high speed becomes very difficult to hear. FIG. 3 shows a general HIFI audio processing circuit block at the time of reproduction. In the drawing, reference numerals 1 and 2 denote audio heads mounted on a rotating drum 3, 4 and 5 denote preamplifiers, 6 denotes a switch circuit, and 7 and
8, each center frequency band pass filter (BPF) is 1.3M _HZ, 1.7M _HZ. Reference numerals 9 and 10 denote FM demodulation circuits, reference numerals 11 and 12 denote pre-hold circuits, reference numerals 13 and 14 denote Lch and Rch audio output terminals, and reference numeral 15 denotes switching for generating a head switching signal from a detection pulse of the rotation detector 16 of the rotary drum 3. The switch circuit 6 and the hold circuits 11 and 12 are switched by a signal from the pulse generation circuit 15.

An audio signal processing device for special reproduction of a HIFI-VTR is disclosed in Japanese Patent Laid-Open Publication No. Sho 63
Japanese Patent Publication No.-214088 (H04N 5/93), however, the relevant publication uses an analog / digital converter / memory and the like, so that the cost is greatly increased.

[0005]

SUMMARY OF THE INVENTION The HIFI audio signal processing apparatus of the present invention reduces noise, especially buzz, of fast-reading audio during double-speed reproduction in a popular VTR.

[0006]

According to the present invention, there is provided a magnetic recording and reproducing apparatus for recording and reproducing a frequency-modulated audio signal (hereinafter referred to as a HiFi audio signal) on a video recording track. An audio signal processing circuit comprising a band-pass filter (hereinafter referred to as a BPF) and an FM demodulation circuit is provided. The BPF is provided with a switching means for switching band characteristics. The pass band before demodulation of the signal is made narrower than during normal reproduction. Further, a pre-hold circuit is connected to an output terminal of the FM demodulation circuit, and a time constant changing means for changing a time constant is provided in the pre-hold circuit. The high frequency component after demodulation of the audio signal is removed. A mixing circuit that mixes the L-channel and R-channel audio signals of the HiFi signal that have passed through the audio signal processing circuit; a smoothing circuit that smoothes the audio signal mixed by the mixing circuit with a predetermined time constant; Comparing the output from the smoothing circuit with a predetermined reference, and outputting a mute signal for muting the output of the audio signal when the output from the smoothing circuit is smaller than a predetermined reference value. I do.

[0007]

The double-speed playback operation narrows the bandwidth of the BPF, removes out-of-band noise, switches the time constant of the hold circuit, and slightly cuts the high-frequency portion of the frequency characteristics. An easy-to-read voice can be obtained.

[0008]

FIG. 1 shows an example of a reproducing HIFI audio signal processing apparatus according to the present invention, and FIG. 2 is a frequency characteristic diagram of a BPF. The same parts as those in the conventional example are denoted by the same reference numerals and description thereof will be omitted. In FIG. 1, reference numerals 17 and 18 denote bandwidth-variable BPFs, reference numerals 19 and 20 denote time-constant type pre-hold circuits, reference numeral 21 denotes a control signal input terminal at the time of double speed reproduction, and reference numeral 22 denotes a time constant changing circuit of the BPFs 17 and 18. , 23 are time constant changing circuits for the hold circuits 19 and 20, 24 is a mixing circuit, 25 is a smoothing circuit for smoothing with a time constant 26, 27 is a comparing circuit for comparing with a reference value, and 28 is an audio output mute circuit (FIG. (Not shown). The mixing circuit 24, the smoothing circuit 26, the comparison circuit 2
7 constitutes an audio signal detecting means.

Next, the operation will be described. In FIG. 1, during normal standard reproduction, an FM-modulated audio signal reproduced by an audio head 1 or 2 is amplified by a preamplifier 4 or 5, and then operated by a switching pulse from a switching pulse generating circuit 15. are switched becomes continuous signal at 6, through respectively by BPF17 and BPF18 center frequency 1.3M _HZ and 1.7 M _HZ · bandwidth W _1, is demodulated in the next stage of the FM demodulation circuits 9 and 10, the after being pre-held in the location-hold circuits 19 and 20 before operating at switching pulse at each time constant T _1, respectively, from an output terminal 13 and 14 Lch, audio signal Rch is output. The signals passing through the hold circuits 19 and 20 are mixed by a mixing circuit 24, smoothed to a direct current by a smoothing circuit 25 having a time constant 26, and a reference value V is output by a comparison circuit 27.
_If it is compared with ₁ and is equal to or less than the reference value, a mute signal is output to the terminal 28 to mute the audio output.

During double-speed playback, the terminal 21 is operated by the operation.
, A time constant of the time constant changing circuit 22 is switched, and the bandwidth of the BPFs 17 and 18 is changed from W ₁ to W ₂ (W ₁
> W ₂ ). Further, the time constant of the time constant changing circuit 23 is switched to switch the hold time constant of the hold circuits 19 and 20 from T ₁ to T ₂ (T ₁ <T ₂ ). Accordingly, the frequency characteristics of the BPFs 17 and 18 at the time of double speed reproduction are narrower than those at the time of normal reproduction (solid line) as shown by the dotted lines in FIG. 2, and unnecessary out-of-band noise components are completely removed.

As described above, at the time of double speed reproduction, the BPF 1
Although the bandwidths 7 and 18 are narrowed to remove some extra high-frequency portions of the modulated signal, there is no problem with sound quality.
Also, by increasing the time constants of the hold circuits 19 and 20,
By slightly cutting the high frequency range of the frequency characteristic, the sound becomes easy to hear. Note that the configuration of the present invention obtains a mute signal by smoothing and comparing the audio output, and mutes the audio output when the audio signal is not signaled or unmodulated. Removed.

[0012]

According to the structure of the present invention, the HI at the time of double speed reproduction is obtained.
The noise of the FI sound and the buzz sound at the time of non-modulation can be removed, and there is an effect that a sound that is easy to hear can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of the present invention.

FIG. 2 is a frequency characteristic diagram of a bandpass filter.

FIG. 3 is a circuit block diagram of a conventional example.

[Explanation of symbols]

 9,10 FM demodulation circuit 17,18 BPF 19,20 Pre-hold circuit 22,23 Time constant changing circuit 24 Mixing circuit 25 Smoothing circuit 27 Comparison circuit

Claims (3)

(57) [Claims] 1. A magnetic recording / reproducing apparatus for recording / reproducing an audio signal (hereinafter, referred to as HiFi audio signal) frequency-modulated on a video recording track, comprising: an audio signal comprising at least a band pass filter (hereinafter, referred to as BPF) and an FM demodulation circuit. A signal processing circuit, a switching means for switching the band characteristic in the BPF, and switching the band characteristic of the BPF at the time of double-speed reproduction, so that the pass band before demodulation of the HiFi audio signal is made narrower than that at the time of the normal reproduction. Characteristic audio signal processing device. 2. A pre-hold circuit is connected to an output terminal of the FM demodulation circuit, and a time constant changing means for changing a time constant is provided in the pre-hold circuit, and the time constant is changed at the time of double speed reproduction. 2. The audio signal processing device according to claim 1, wherein a high-frequency component after demodulation of the HiFi audio signal is removed. 3. The HiF that has passed through the audio signal processing circuit.
a mixing circuit for mixing the L-channel and R-channel audio signals of the i signal, a smoothing circuit for smoothing the audio signal mixed by the mixing circuit with a predetermined time constant, and an output from the smoothing circuit being predetermined. 3. A comparison circuit for comparing a reference with a reference and outputting a mute signal for muting the output of the audio signal when an output from the smoothing circuit is smaller than a predetermined reference value.
An audio signal processing device as described in the above.