JP2517429B2 - Tone multi-mode discrimination circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a discriminating circuit capable of stably discriminating a multiple mode of an audio signal.

(B) Conventional Technology For example, Japanese Patent Application Laid-Open No. 62-6586 (H04N 5/91) discloses a configuration for recording a discrimination signal in order to discriminate the audio multiplex mode during reproduction.

Basically, there are mono, stereo, and bilingual modes in the audio multiplex mode. The recording method is as follows in the so-called high band 8 mm VTR (high-eight method).

That is, as shown in FIG. 5, in the monaural mode, a single carrier signal of 1.5 MHz is FM-modulated and recorded. In the stereo mode, an L + R signal modulates a 1.5 MHz carrier signal and an L-R signal modulates a 1.7 MHz carrier signal for recording. By doing so, the L + R signal can be reproduced even by a conventional device that does not support the high-eight system.

In the bilingual mode, a carrier signal of 1.5 MHz is recorded in the main voice and a carrier signal of 1.7 MHz is recorded in the sub voice. Therefore, when the tape recorded in the bilingual mode is reproduced in the stereo mode, it passes through the matrix, and the main audio and the sub audio are mixed and output. Therefore, in order to eliminate such inconvenience, it is necessary to discriminate the recording sound multimode at the time of reproduction and switch the circuit.

Therefore, in the high-eight system, in the bilingual mode, at the time of recording, the carrier levels of 1.7 and 1.5 MHz in the vertical blanking period of the video signal are set to be approximately doubled. Then, at the time of reproduction, it is only necessary to discriminate between the stereo mode and the bilingual mode depending on the difference in the level.

(C) Problem to be Solved by the Invention As described above, in the hiight system, bilingual / stereo mode discrimination is performed depending on whether or not the level of the voice FM carrier is large in the vertical blanking period. However, the reproduction output of the head constantly fluctuates during reproduction, and the output level between the heads also varies.
Further, the discrimination circuit must be configured so that no malfunction occurs during special reproduction.

(D) Means for Solving the Problem In the present invention, in order to stably detect a pilot signal whose level increases only in a predetermined section, a detection means for obtaining an envelope of a reproduction signal and a period of the emphasized level are extended. Means, a means for shifting the DC level of the output of the detection means to a larger direction, and a comparing means for comparing the outputs of the extending means and the shifting means, and means for discriminating the mode based on the output of the comparing means. ing.

(E) When comparing the signal with the extended period and the signal without extended action level, a large difference appears in the case of the signal with the enhanced level, but at a predetermined timing of the level In the case of a signal that has not been emphasized, no difference occurs. Therefore, by utilizing this difference, the determination can be performed without being affected by the signal level.

(F) Embodiments Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the embodiment, and FIGS. 2, 3, and 4 are waveform diagrams for explaining the operation.

In the figure, 1 is a bandpass filter, 2 is an amplifier,
3 is a detector, 4 is an amplifier, 5 is a holding means, 6 is a hold pulse generator, 7 is a DC amplifier, 8 is a voltage comparison comparator, 9 is a counter, 10 is a reset pulse generator, 11 is a latch circuit, 12 is a latch pulse generation circuit, 13
Is a tape, 14 is a magnetic head, and 15 is a latch control circuit.

The band pass filter 1 extracts a 1.5 MHz or 1.7 MHz voice carrier. The output of the holding means 5 is input to the positive side input of the comparator 8, and the DC amplifier 7 is input to the negative side input.
Output is being supplied. When the positive input voltage is high, the H level is output, and when the negative input voltage is high, the L level is output.

The hold means 5 includes a hold capacitor and an analog switch, and holds the output level of the amplifier 4 according to the hold pulse from the hold pulse generator 6. The analog switch is connected between the output of the amplifier 4 and the positive side input of the comparator 8. The hold capacitor is connected between the positive side input of the comparator 8 and the reference potential point. That is, when the analog switch is on, the terminal voltage of the hold capacitor changes according to the change in the output of the amplifier 4. When the analog switch is turned off in accordance with the hold pulse, the previous voltage is stored in the hold capacitor.

The hold pulse generator 6 is equipped with a mono-multi, for example, and outputs a hold pulse that rises after a predetermined time delay from the rising and falling edges of the head switching (RF switching) pulse and is at H level for a predetermined period.

A head switching pulse is supplied to the reset pulse generator 10. Then, based on this head switching pulse,
A reset pulse synchronized with the head switching pulse is created and supplied to the counter 9.

The latch pulse creating circuit 12 receives the head switching pulse and creates a clock pulse for the latch circuit 11. The latch control circuit 15 is for controlling the latch operation based on the control signal instructing the special reproduction mode. The simplest configuration is considered to be an analog switch that turns on / off the signal path of the latch pulse from the latch pulse generation circuit 12.

The latch circuit 11 is composed of one or a plurality of D type latch circuits.

Next, the operation of the embodiment will be described with reference to FIGS. As described above, in the high-eight method, the voice carrier level is emphasized about twice in the blanking period in the bilingual mode. Therefore, if the wave is properly detected, a waveform similar to b will be obtained with respect to the head switching signal B (see FIG. 2).

Therefore, the hold pulse C is created as a pulse that rises during the period when the detection output is at the H level and falls until the edge of the next head switching pulse. Such a pulse can be created by using mono-multi based on the edge of the head switching signal.

FIG. 3 is a waveform diagram for explaining the comparison operation.
The reproduction output from the head 14 includes a difference in output level between the heads as shown in (b).

A signal of a predetermined frequency is extracted from such a reproduction output,
When the envelope is detected and DC amplification is performed, the waveform becomes as shown in C. On the other hand, the waveform after the hold operation is performed on the signal before the DC amplification is as shown in FIG.
At the output of the DC amplifier 7, the DC level is amplified (level shift in the increasing direction).

A voltage comparison is made between the C and D signals. This is shown in E. Here, in the shaded portion, the output of the holding means 5 becomes larger than the output of the DC amplifier 7, and therefore a pulse that is at the H level during this period is obtained. This is the case in bilingual mode.

When not in the bilingual mode, the holding means 5
Since the output level of 1 does not exceed the level of the DC amplifier 7, the output of the comparator 8 is always L level. DC
The reason why the level shift is performed using the amplifier 7 is to ensure the L level state of the output of the comparator 8 in the non-birigal mode.

The output of the comparator 8 has a relationship with the head switching pulse as shown in FIG. Further, in the embodiment, in order to prevent erroneous discrimination due to noise mixing, bilingual discrimination is made when a predetermined number or more pulses are generated from the comparator. The counter 9 is used for that purpose.

The reset pulse (FIG. 3C) is supplied to the counter 9. This reset pulse (Fig. 3C) is created in this embodiment by triggering, for example, a monomulti, based on one edge of the pulse obtained by dividing the head switching pulse (Fig. 3B) by 1/2. It In FIG. 3, it occurs at every other falling edge of the original head switching pulse. That is, the cycle of the reset pulse is twice as long as that of the head switching pulse.

Further, in the embodiment, when two pulses from the comparator 8 are counted, the output of the counter 9 becomes H level (see FIG. 3B and D). Then, the output of the counter 9 is latched at a predetermined timing to obtain a continuous determination output of H level or L level.

In the embodiment, the latch pulse is created in synchronization with the head switching pulse, and its cycle is D, which is the same as the cycle of the reset pulse, and is a signal delayed by one cycle of the head switching pulse. By using such a latch pulse, the output of the counter 9 can be held without error and continuous level output can be obtained. Then, the reproduction signal is output from the latch circuit 11 to a stereo matrix circuit (not shown).
Is controlled.

In special reproduction mode (during high-speed reproduction, etc.), the special reproduction control signal becomes H level, the analog switch of the latch control circuit 15 is turned off (in the configuration in which the latch pulse is bypassed, it is turned on), and a new latch operation is performed. Is not performed and the previous determination result is retained. This is because during the special reproduction, the level of the reproduction output changes greatly and the possibility of misjudgment increases.

In the embodiment, two outputs of the comparator 8 are determined to be bilingual when they occur within the reset pulse cycle (N = 2), but this N is set to a higher number (for example, four). It is also possible. Further, in order to make a more reliable judgment, a signal obtained by latching the output of the comparator 8 at a predetermined timing may be supplied to the counter 9.

(G) Effect of the Invention As described above, according to the present invention, it is possible to reliably determine a multi-tone mode such as bilingual, which is advantageous.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment, FIG. 2, FIG. 3 and FIG. 4 are waveform diagrams for explaining the operation, and FIG. 5 is an explanatory diagram for explaining a polyphonic system of 8 mm VTR system. is there. 1 ... band pass filter, 3 ... detection circuit, 5 ... holding means, 8 ... comparison circuit (comparator), 9 ...
Counter, 11 …… Latch, 14 …… Head.

Claims (1)

(57) [Claims] 1. A means for reproducing a signal from a medium in which the level of a voice carrier signal is emphasized for a predetermined period in accordance with a polyphonic mode, a means for extracting the carrier signal from the reproduced signal, and an extraction. Detecting means for detecting the envelope of the generated carrier signal, extending means for extending the corresponding period by holding the level of the period corresponding to the predetermined period in the output of the detecting means, and output and extension of the extending means. A sound multi-mode discriminating circuit, which comprises a comparing means for comparing a signal not reproduced, and discriminates a sound multi-mode by the output of the comparing means.