JPH04176280A - Stereo/monoral decision device - Google Patents

Abstract

PURPOSE:To reduce adverse effect due to misjudgement by taking out the level difference of each input audio signal and delaying the output signal after level decision based on the signal with this level difference, and turning this delay output signal to be a stereo/monoral decision signal. CONSTITUTION:An attenuator 32 is inserted and connected to the input side of the sum signal (L+H) components of a comparison device 31. The output signal from the comparison device 31 is sent to a delay circuit 34. In this delay circuit 34, a delay output signal (l) from a comparison device 39 indicates stereo at the time of 'H' and monoral at the time of 'L' respectively, to be sent to a three input AND gate 27. The 'H' is outputted from an output terminal 29 as the stereo only when all the stereo/monoral decision due to the stereo pilot signal at the time of TV broadcasting, the output signal from a hysterisis decision circuit part 20, and the output signal from a delay circuit 34 are decided as stereo H from the three input AND gate 27.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a stereo/monaural discrimination device that discriminates whether an input audio signal is a stereo signal or a monaural signal.

[Summary of the invention]

The present invention provides a stereo/monaural discrimination device for discriminating whether a two-channel audio input signal is a stereo signal or a monaural signal. By delaying the output signal that has been discriminated and using this delayed output signal as a stereo/monaural discrimination signal, it is possible to perform stereo/monaural discrimination that reflects the steady trend of the input audio signal, and also to distinguish between each input audio signal. Stereo/
By performing monaural discrimination, effective discrimination is performed.

[Conventional technology]

It is performed to determine whether the input audio signal is a two-channel audio signal, a stereo signal, or a monaural signal, and to switch and control various signal processing contents for the input audio signal according to the result of this determination.

For example, in recent years, it has become common to perform so-called sound field expansion processing on input audio signals to enhance the sense of reality.This sound field expansion processing is processed depending on whether the input signal is a stereo signal or a monaural signal. The content needs to be different.

In other words, various sound field expansion processing methods for expanding the sound field can be roughly divided into stereo sound field expansion methods that expand the sound field of a stereo input signal, and methods that transform a monaural input signal into a pseudo stereo signal or a signal with a more realistic feeling. Is there a monaural sound field expansion method that expands the sound field, or is there a circuit for the stereo sound field expansion method?
In principle, it operates normally only for stereo audio input signals, and only provides sufficient sound spread when the input signal is a monaural audio signal. Conversely, if a stereo audio signal is input to a monaural sound field expansion (for example, pseudo-stereo) circuit, there is a possibility that an unnatural feeling may occur. As described above, since different processing is required depending on whether the input audio signal is stereo or monaural, a stereo/monaural discrimination circuit that can reliably discriminate between stereo and monaural is desired.

[Problem to be solved by the invention]

By the way, in television broadcast signals, it is possible to distinguish between stereo and monaural by detecting the presence or absence of a so-called stereo pilot signal that is selectively superimposed on the broadcasting station side. If a stereo pilot signal is superimposed even though it is a monaural audio signal, as in the case of insertion, the stereo pilot signal will be detected and determined to be stereo, and the result will be incorrectly determined. This results in inappropriate sound field expansion processing or the like being performed.

Another disadvantage is that this stereo picograph signal can only be used for television broadcast signals, and cannot be applied to audio signals from other sources (VTR, video disc, audio disc, etc.). .

In addition, as a method for determining from the input audio signal itself, it is possible to determine whether it is stereo or monaural by level-discriminating the difference signal of the two-channel input audio signal, but even if it is a stereo signal, the sound image is localized to the center. If there is a sudden change, such as when there is Furthermore, when determining the absolute level of an input audio signal, there is a risk that the determination may become unstable when the input level is low.

The present invention has been made in view of the above circumstances, and provides a stereo/monaural discrimination device that can effectively discriminate whether a supplied audio signal is stereo or monaural, and that can reduce the negative effects of erroneous discrimination. The purpose is to provide.

[Means to solve the problem]

A stereo/monaural discrimination device according to the present invention includes a pair of input terminals to which two-channel audio signals are supplied;
a difference component detection circuit that extracts the level difference between the audio signals of each channel supplied to the pair of input terminals;
It has at least a level discrimination circuit that discriminates the level based on the output signal from this difference component detection circuit, and a delay circuit that delays the output signal from this level discrimination circuit, and the output signal from this delay circuit is stereo/ The above problem is solved by using a monaural discrimination signal.

Further, the stereo/monaural discrimination device having the above configuration includes a sum component detection circuit for extracting a level sum of two channel audio signals supplied to the pair of input terminals, and the level discrimination circuit The above problem is solved by a stereo/monaural discrimination device that performs a relative level discrimination operation based on the ratio of the output signal from the component detection circuit and the output signal from the two-signal component detection circuit.

[For production]

By delaying the level discrimination output signal of the level difference signal between the two channel input audio signals, even if a sudden input change occurs, the discrimination result does not change suddenly, and misjudgment can be prevented. In addition, by performing relative level discrimination based on the ratio between the level difference and the level sum of each input audio signal, instability in the discrimination operation due to fluctuations in the absolute level, etc. is avoided, and the stability of the operation is increased. ing.

〔Example〕

FIG. 1 is a block circuit diagram showing an embodiment of a stereo/monaural discrimination device according to the present invention.

In this FIG. 1, the pair of input terminals 11 and 12 have
Two channels of audio signals, for example left and right stereo audio signals, or monophonic audio signals that are the same, are supplied. Each input audio signal from these input terminals 11.12 (
L, R) are sent to the 7-trix circuit 13, and the difference (L-R) and sum (L+R) of each signal are calculated. That is, the adder (subtracter) 15 in the matrix circuit 13 subtracts the input signal (R) at the terminal 12 from the input signal (L) at the terminal 11 to obtain a difference signal (L-R), and the adder 16
Then, the input signal (T, ) of the terminal 11 and the input signal (R) of the terminal 12 are added to obtain a sum signal (L+R). The difference signal (LR) and sum signal (L+R) from matrix circuit j3 are sent to peak hold circuits 17 and 18, respectively. These peak hold circuits 17.
Reference numeral 18 is used as a specific example of a signal level detection circuit, which detects the positive peak value of each supplied signal, holds it at a predetermined time constant, and outputs it. From these peak hold circuits 17 and 18, each input audio signal (L,
Signals representing the level difference and level sum of R) are extracted.

In the embodiment of the present invention, each hold time constant of the peak hold circuits 17 and 18 is set to several tens of ms.
(milliseconds), and the difference signal (L-R
) The time constant of the peak hold circuit 18 on the sum signal (L+R) side is set approximately 1.3 to 1.5 times longer than the time constant of the peak hold circuit 17 on the ) side. As a result, the input signal suddenly disappeared (level decreased)
Sometimes, it is determined that it is monaural, as is clear from the determination operation described later, so that the determination operation is prevented from becoming unstable. If each hold time constant is shorter than the tens of ms mentioned above,
There is a possibility that a misjudgment may occur.

Note that if such an effect is not required, the order of the matrix circuit 13 and the peak hold circuits 17 and 18 is reversed, and each signal level of the two channels of input audio signals is detected first. The difference or sum of these detected levels may be calculated. Further, instead of the peak hold circuits 17 and 18, various signal level detection circuits such as an envelope detection circuit may be used.

The level difference signal of the two-channel input audio signals (L, R) obtained in this way, that is, the output signal from the peak hold circuit 17, for example, is sent to a hysteresis discrimination circuit unit 20 that performs level discrimination with hysteresis.
is being sent to. This hysteresis discrimination twisting section 20 is
For example, it includes two comparators (level discriminators) 21 and 22 and a hysteresis circuit 23. Comparator 2
1 is provided for discriminating the upper level of the hysteresis, and a first reference voltage v1 corresponding to the upper level of the hysteresis is supplied to the inverting (-side) input terminal. Therefore, this comparator 21 is H'' when the level of the signal supplied to the non-inverting (+ side) input terminal is equal to or higher than the first reference voltage 73.

(high level). The comparator 22 has a non-inverting (+ side) input terminal with a second reference voltage V2 (v+
>V2), and performs a level discrimination operation in which the signal level supplied to the inverting input terminal becomes 'H' when the signal level is equal to or higher than the second reference voltage 72. Therefore, for example, from the peak hold circuit 17, When a level difference signal as shown in a in FIG. The level discrimination output (comparison output) signals of are as shown in c and d of FIG. In response to the rising edge of output signal C, the output changes from L''' (low level) to H''', and comparator 2
In response to the rising edge of the output signal d from 2, the output becomes “H”
It performs a switching operation in which the output from the hysteresis circuit 23 changes from ``H'' to ``L'', and when the output from this hysteresis circuit 23 is ``H'', it is stereo, and when it is ``L'', it is monaural (the final determination will be described later). (preliminary determination prior to final determination) is performed. As this hysteresis circuit 23, a so-called positive edge trigger type S-R (set-reset) flip-flop can be used, and the comparator 21
The output signal from the comparator 22 may be supplied to the set terminal, and the output signal from the comparator 22 (via the switch 25, which will be described later) may be supplied to the reset terminal.

Note that various configurations such as a so-called Schmitt trigger are possible as a circuit for performing a level discrimination operation with hysteresis like the hysteresis discrimination circuit section 2o.

By the discrimination operation with hysteresis as described above, that is, when the level difference between the two channel input audio signals is equal to or higher than the first reference voltage V, stereo is determined, and the second reference voltage lower than this voltage v1 is determined. When the voltage is lower than V2, it is determined that it is monaural, and a difference is made between each discrimination level. In the state between these discrimination levels, the previous discrimination result is maintained, and noise superimposition is prevented by giving hysteresis to the discrimination. This prevents the negative effects of misjudgment when the level difference changes in a short period of time, such as when the stereo sound field is centered, and achieves effective and accurate stereo/monaural discrimination based on the actual situation. ing.

In the embodiment of the present invention, a switch 25 is inserted and connected between the comparator 22 and the hysteresis circuit 23, and when the switch 25 is off, the output signal from the comparator 22 is not transmitted to the hysteresis circuit 23. , the above reset operation (operation to change the output from "H" to "L")
is prohibited. This switch 25 controls the level (
On/off control is performed according to an output signal obtained by level-discriminating the level sum (level sum) at a predetermined level (third reference voltage) L.

That is, the level sum signal (for example, the output signal from the peak hold circuit 18) is sent to the non-inverting (+ side) input terminal of the comparator (level discriminator) 24, and the inverting (+) input terminal of the comparator 24 - side) The third reference voltage V3 is supplied to the input terminal. Therefore, this comparator 24 performs a level discrimination operation in which it outputs 'H' (high level) when the signal level (above level sum) of the non-inverting (+ side) input terminal is equal to or higher than the third reference voltage 73. Specifically, when the above level sum signal becomes as shown in b in Fig. 2,
The comparison output (level discrimination output) signal from the comparator 24 is as shown in Fig. 2 e, and when this signal e is "H",
The switch 25 in the hysteresis discrimination circuit section 20 is turned on (conducting). The switch 25 has the comparator 2
Since a signal as shown in FIG. 2d from switch 2 is supplied, the output signal from switch 25 becomes as shown in FIG. 2f, and is sent to the hysteresis circuit 23. Therefore, the output from the hysteresis circuit 23 is
At the rising edge of the signal from the comparator 21 shown in FIG.
At the rising edge of the signal shown in Figure 2 f from
″→′°L′”. Therefore, the output signal from the hysteresis circuit 23 is as shown in g in Fig. 2, and this output signal g corresponds to stereo when it is "H" and monaural when it is "L". When viewing the hysteresis circuit 23 as a rising edge trigger type S-R flip-flop, it can be considered that the reset operation is inhibited by the output signal from the comparator 22 or by turning off the switch 25.

Alternatively, it can be seen that the discrimination operation from stereo to monaural is prohibited by turning off the switch 25.

Here, the effect of level discrimination with hysteresis is as described above, or the comparator 24
By providing the switch 25, the following effects are obtained. That is, when the level of the sum of the two-channel input audio signals becomes less than the predetermined level 3, the switch 25 is turned off and the operation of the hysteresis discrimination circuit section 20, especially the reset operation of the hysteresis circuit 23 (i.e., from stereo to monaural) is turned off. (discrimination operation) to prevent erroneously determining that the input signal is monaural when the overall level of the input signal is very small. This is done in consideration of the fact that when the input level is low, it is difficult to distinguish between stereo and monaural, and misidentification is likely to occur.Especially when switching the sound field expansion processing described above depending on stereo/monaural, it is necessary to Considering that the sound field expansion process may cause a sense of discomfort, the switching operation from stereo to monaural is prohibited to prevent the adverse effects of misjudgment.

The output signal from the hysteresis circuit 23 is the output signal from the hysteresis discrimination circuit section 20 and represents the stereo/monaural discrimination result (preliminary discrimination prior to the final stereo/monaural discrimination described later). can be,
3-person power AND Kay 1.27 has been sent.

Next, the input audio signals of the above two channels (L, R
), a level difference signal representing the level of the difference signal (I, -R);
For example, the output signal from the peak hold circuit 17 is sent to the non-inverting (+ side) input terminal of the comparator (level discriminator) 31, and a level sum signal representing the level of the sum signal (L + R), for example, the peak The output signal from the hold circuit 18 is sent to the inverting (-) input terminal of the comparator 24 via an attenuator 32. The attenuator 32 attenuates the input signal level to 1/7, for example, and outputs the attenuated signal level.

Here, when a specific example of the level ratio of each of the above-mentioned signals (L-R) and (L+R), for example, the level of the signal (L-R)/(L+R), is 11 in FIG. The switching threshold (discrimination level) of the comparator (level discriminator) 31 is 1/7, and the output from the comparator 31 is as shown in i in FIG.

In this comparison output signal 1, "H" (high level) corresponds to stereo, and "L" (low level) corresponds to monaural.

Generally, this is done by comparing the levels of the (L-R) component and the (L+R) component, and the (L-R) component is set at a certain ratio (for example, 115 to 1/9) to the (L+R) component. ) or above, it is determined as stereo.

Here, the (L + R) component of the input audio signal is (L-
The level is higher than that of the R) component, and it is better to attenuate this (L + R) component than to amplify the (L-R) component.
Taking into consideration the fact that errors due to offsets, etc. can be reduced,
In this embodiment, in order to obtain the above constant ratio, the comparator 31
An attenuator 32 is inserted and connected to the input side of the (L + R) component.

The output signal from the comparator 31 is processed by a delay circuit 3 in which the delay time is different between the rising edge and the falling edge of the signal.
It has been sent to 4. This delay circuit 34 includes a switch 3 which is controlled on/off according to an output signal from a comparator 31.
5, a resistor 36 with a resistance value R connected at one end to this switch 35, and a current (2) connected to the other end of this resistor 36.

a current source 37 that flows, and a capacitor 38 having a capacitance value C, one end of which is connected to the connection point between these resistors 36 and the current source 37.
The other ends of the switch 35 and the capacitor 38 are grounded. The terminal voltage of the capacitor 38 is supplied to the inverting (- side) input terminal of the comparator 39, and is compared with the fourth reference voltage V4, which is supplied to the non-inverting (+ side) input terminal of the comparator 39, to determine the level. It is now being discriminated against.

In this delay circuit 34, when the switch 35 is off, a current ■ from the current source 37 is generated. flows into the capacitor 38 and is charged, and when the switch 35 is on, the charge in the capacitor 38 is discharged via the resistor 36. When the comparison output from the comparator 31 is H'', the switch 3 is
5 is turned on, the capacitor 38 is charged and discharged as shown in FIG. 3j in response to the comparison output signal 1 shown in FIG. 3, and the terminal voltage changes as shown in FIG. By level-discriminating this terminal voltage k using the fourth reference voltage 4, a delayed output signal as shown in FIG. 3 is obtained from the comparator 39. This output signal p is also similar to the above signal i, ゛H
'' represents stereo, and ``L''° represents monaural.

Here, as is clear from 1 in Figure 3, monaural (
The delay time τ1 for switching from "L") to stereo ("H") is shortened to, for example, about several + ms (Mi'J seconds),
The switching delay time τ2 from stereo (H'') to monaural ("L") is set to be as long as, for example, several seconds.This is because instantaneous silence is ignored during monaural discrimination,
This is to be able to respond to rapid changes in the input audio signal during stereo discrimination.

In the embodiment of the present invention, the upper limit (for example, 5.2 V) and the lower limit (for example, OV
) The above voltage v4 is set in the upper limit range between 4.
OV), the delay time τ at the rise of the comparison output signal 1 (at the rise of the delayed output signal!),
(and the delay time τ2 at the falling edge is increased. Specifically, for example, the resistance value R is set to 56Ω, the current I
. When the voltage is 10 μA and the capacitance value C is 10 μF, the rise delay time τ1 is 0.16 s, and the rise delay time τ2 is 48 seconds. In addition, for example, the capacitor 38
The respective delay times can also be made different by making the discharging time constant and the charging time constant different from each other.

Also, the relationship between the on/off of the switch that operates according to the output from the comparator 31 and the charging and discharging of the capacitor, and the positive and negative polarity (inverted , non-inversion) can be arbitrarily changed.In short, each circuit constant may be set so as to shorten the delay time during stereo discrimination and lengthen the delay time during monaural discrimination.

The output signal from such a delay circuit 34 is
It is sent to D gate 27.

This three-man power AND gate 27 further has an input terminal 28.
Stereo pilot signals are also supplied from This stereo pilot signal is obtained by detecting a stereo pilot signal inserted into a television broadcast signal, and indicates stereo when it is "H".

However, when the audio signal supplied to the input terminal 1112 is other than the audio signal of television broadcasting, the signal supplied to the input terminal 28 is configured to be H''°.

Therefore, this three-man-powered AND gate 27 can perform stereo/monaural discrimination based on the stereo pilot signal in the case of television broadcasting, and the hysteresis discrimination circuit section 20.
Stereo/monaural discrimination based on the output signal from the delay circuit 34 and stereo/monaural discrimination based on the output signal from the delay circuit 34. Only when stereo (PaH''') is determined, the final discrimination result is set to stereo, Output terminal 29
"H" is output from. This makes it possible to perform discrimination that takes advantage of the strengths of each of the three types of stereo/monaural discrimination.

In other words, in the discrimination based on the stereo pilot signal, the fact that the pilot signal is always monaural when there is no pilot signal is utilized, and the level discrimination of the difference signal (L-R) and/or the level of the sum signal (L + R) is performed. Absolute level discrimination using discrimination can detect instantaneous changes in the input audio signal, while relative level discrimination by comparing the levels of the difference signal (LR) and sum signal (L+R) can detect steady trends in the input. can be determined. Therefore, more accurate and effective stereo/monaural discrimination can be performed than discrimination using one of these types.

The stereo/monaural discrimination output signal obtained in this way is 1, for example, as a stereo/monaural switching display signal.
Alternatively, it is used as a switching signal for switching between stereo sound field expansion and monaural sound field expansion in the sound field expansion processing device.

Note that the present invention is not limited to the above-mentioned embodiments; for example, the final discrimination result may be obtained by only one type of stereo/monaural discrimination, or other types of stereo/monaural discrimination may be combined. You can do it like this. Further, the output determined by level discrimination of the LR signals may be supplied to the delay circuit 34.

〔Effect of the invention〕

As is clear from the above explanation, the stereo/monaural discrimination device according to the present invention extracts the level difference between the input two-channel audio signals, and performs level discrimination based on the extracted level difference signal. Since the stereo/monaural discrimination signal is obtained by delaying the output, it is possible to prevent erroneous discrimination when the level difference changes due to a sudden change in the input audio signal. In addition, by delaying the relative level discrimination output that determines the level based on the ratio between the level sum of each input audio signal and the above level difference to obtain a stereo/monaural discrimination signal, stable stereo/monaural discrimination operation that is resistant to absolute level fluctuations is achieved. I can do it.

Furthermore, as in the embodiments of the present invention, by setting the delay time relatively long during monaural discrimination and relatively short during stereo discrimination, momentary silence during monaural discrimination can be ignored; It is possible to respond to sudden changes in input when making a step-1-no-o determination.

Further, according to the embodiment of the present invention, in combination with the stereo/monaural discrimination using the level discrimination output of the level difference, the final stereo Since /monaural discrimination is performed, it is possible to perform stereo/monaural discrimination not only by determining a steady trend by the above-mentioned relative level discrimination but also by taking into account instantaneous changes in the input audio signal by the above-mentioned absolute level discrimination. Furthermore, by performing the final stereo/monaural discrimination in combination with the stereo/monaural discrimination result based on the stereo pilot signal of the television broadcast signal, the reliability and certainty of the discrimination result can be further improved.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram showing an embodiment of a stereo/monaural discrimination device according to the present invention, and FIGS. 2 and 3 are time charts for explaining the operation of the embodiment. 11.12...Audio signal input terminal
13...Matrix circuit 15.16...Adder 17.18...Peak hold circuit 20...
...Hysteresis discrimination circuit section 21.22.24.31
．． 39...Comparator 23...Hysteresis circuit 25.35...Switch 27...3 manual AND gate 28...Stereo pilot signal input terminal 29
...Stereo/monaural discrimination signal output terminal 34...
...Delay circuit 38...Capacitor

Claims (2)

[Claims] (1) A pair of input terminals to which two-channel audio signals are supplied, a difference component detection circuit that extracts the level difference between the audio signals of each channel supplied to these pair of input terminals, and at least this difference component detection circuit. A level discrimination circuit that discriminates a level based on an output signal from the level discrimination circuit, and a delay circuit that delays the output signal from this level discrimination circuit, and the output signal from this delay circuit is used as a stereo/monaural discrimination signal. A stereo/monaural discrimination device featuring: (2) It has a sum component detection circuit that extracts the level sum of the two-channel audio signals supplied to the pair of input terminals, and the level discrimination circuit detects the difference component between the output signal from the sum component detection circuit and the difference component. A claim characterized in that a relative level discrimination operation is performed based on a ratio with an output signal from a circuit
1) The stereo/monaural discrimination device described above.