JPH0474675B2 - - Google Patents

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an audio signal comparison circuit.

(Prior Art) There is often a need to determine whether two audio signals are the same. However, "identical" here does not mean that the instantaneous signal voltages are strictly equal, but rather refers to whether the signals obtained from two different receivers are related to the same broadcast. be.

By the way, when performing the above discrimination, it is possible to directly compare two signals using a voltage comparator using a differential amplifier such as an operational amplifier, and then use the result to determine whether the audio signals are the same or not. In this type of method, since the instantaneous voltages of the signals are directly compared, the levels of the two audio signals must be adjusted within a range that can be considered sufficiently equal compared to the sensitivity of the voltage comparator. That is, a voltage comparator that uses an operational amplifier or the like as it is has a very high gain, so even if the same audio signal is input, the output will be saturated even with slight voltage fluctuations. Furthermore, since the audio signals to be compared are usually detected from different circuits, it is not only extremely difficult but also uncommon to manage these signals to the same level. Furthermore, if a delay occurs between two audio signals due to a difference in transmission path, etc., there is a problem that the comparison output will show an inconsistency even though exactly the same signal is input.

On the other hand, apart from the above method, there is also a method of digitizing audio signals and making delicate comparisons, but this method is extremely complex, large, and expensive, and therefore lacks versatility.

(Object of the Invention) The present invention has been proposed in view of the above points, and it is an object of the present invention to provide an audio signal comparison circuit that has a simple configuration and can determine whether two audio signals are the same or not with sufficient accuracy. With the goal.

(Structure of the Invention) FIG. 1 is a block diagram showing an embodiment of the invention. In the figure, A and B indicate two audio signals to be compared, and one of the first audio signals A is selected by a changeover switch SW to be passed through the audio signal inverting circuit 1 or directly applied. The second audio signal B is applied directly to the second low-pass filter 4. here,
The reason why the audio signal inversion circuit 1 is provided is that even if the audio signals to be compared are substantially the same, one of them may be inverted due to the characteristics of the amplifier at the detection point, so this is to deal with such cases. This is because the polarity of the first audio signal A is checked in advance and the changeover switch SW is set. Further, the first and second low-pass filters 2 and 4 are provided to cut high frequency components within a range that allows identification of the first audio signal A and the second audio signal B, and to facilitate comparison. In practice, a low-pass filter of about 2 (KHz) is used.

Next, the output signals of the first and second low-pass filters 2, 4 are input to first and second Δt delay voltage comparators 3, 5, respectively, and
The output signals of the Δt-delayed voltage comparators 3 and 5 are input to the first voltage comparator 6, and the first voltage comparator 6 is followed by a third low-pass filter 7 and a second voltage comparator 8. are connected in sequence and the output OUT is taken out. Here, the first and second △t delay voltage comparators 3 and 5 determine the rising and falling edges of the input signal waveform and output a high-level or low-level signal. For example, as shown in FIG. It is configured as shown in . In Figure 2A, the input signal is divided into two paths by resistors R ₁ and R ₂ , one end of resistor R ₁ is connected to the inverting input terminal of operational amplifier A ₁ , and one end of resistor R ₂ is connected to the non-inverting input terminal. ing. Furthermore, a capacitor C is connected between the non-inverting input terminal of the operational amplifier _A1 and ground. Figure 2 B shows the point shown in Figure 2 A, that is, the operational amplifier A ₁
This figure shows the voltage waveforms at both input terminals and output terminals, where the voltage waveform at point b lags the voltage change at point a by Δt in time due to the delay effect of capacitor C. Here, the delay time Δt is set sufficiently short with respect to the period of the audio signal, and the magnitude relationship between the input audio signal and the signal obtained by delaying this audio signal is determined by the operational amplifier.
By determining based on A ₁ , the change in the audio signal within a minute time, that is, the change in the signal such as the rise and fall of the signal waveform, is converted into a signal that characterizes the change in the signal. That is, during the rising period in which signal a rises with time in Figure 2B, signal b, which is delayed by △t, is always at a lower voltage than the original signal a, and during the rising period in which signal a falls with time. Since the signal b always has a higher voltage than the original signal during the falling period, both periods can be easily distinguished from the magnitude relationship of the voltages. Therefore, operational amplifier _A1 , which receives the voltage signals at points a and b, outputs a low level signal during the rising period of the signal voltage, and a high level signal during the falling period of the signal voltage. The state of change in the audio signal can be characterized by its high and low levels. Note that the polarity of the input terminal of the operational amplifier _A1 is not limited to that shown in FIG. 2A, and may be reversed. However, at this time, the output levels corresponding to the above-mentioned rising period and falling period are inverted.

FIG. 3 specifically shows the first voltage comparator 6 in FIG. The points are connected to the inverting input terminal and non-inverting input terminal of operational amplifier A ₂ through resistors R ₃ and R ₄ respectively, and resistor R ₅ is connected between the inverting input terminal and the output terminal, and between the non-inverting input terminal and ground. are connected to a resistor _R6 , respectively. Here, each resistor must be selected to have an equal amplification degree for both signals so that when signals of the same level are applied to the two input terminals d and e, both signals cancel each other out and the output becomes zero. The following relationship is required: R ₅ /R ₃ =R ₆ /R ₄ . For example, R ₃ = R ₄ = R ₅ = R ₆
By doing so, it functions as a differential amplifier with a gain of 1, and when signals of the same level are input, the output is zero, and when signals of opposite polarity are input, the output is saturated to a low level or a high level.

The operation of comparing audio signals will be described below with reference to the embodiment shown in FIG. Now, the first audio signal A of the first and second audio signals A and B to be determined as identical or non-identical is selected by a changeover switch.
The second audio signal B is input directly or inverted to the first low-pass filter 2 by operating the SW, and the second audio signal B is directly input to the second low-pass filter 4. The first and second low-pass filters 2 and 4 receive the first and second audio signals A,
The high frequency components included in B are cut out, and the output signals are provided to first and second Δt delay voltage comparators 3 and 5, respectively. The first and second △t delay voltage comparators 3 and 5 output low or high level signals according to the rising and falling periods of the signal waveforms sent from the first and second low-pass filters 2 and 4. It outputs a signal and converts it into a pulse-like signal that characterizes the waveform change of the audio signal. Therefore, the amplitude levels of the input first and second audio signals A and B are not affected at all, and therefore audio signals detected from arbitrary points can be compared.

Then, the first voltage comparator 6
The output signals of the △t delay voltage comparators 3 and 5 are compared in voltage, and when both are high level or low level, the output is zero, and when both are different from each other, a low level or high level signal is output. do. That is, if the first and second audio signals A and B are the same, the pulse signals sent from the first and second Δt delay voltage comparators 3 and 5 on both paths will be the same. , the output of the first voltage comparator 6 will be zero, and if the signals are different, positive and negative signals will be output irregularly.
In addition, when comparing the voltages, external noise and voltage fluctuations due to various components are considered, but since the signal input to the first voltage comparator 6 is a signal saturated at a low level or a high level, the first Since the sensitivity of the voltage comparator 6 can be set sufficiently low (gain 1 in the example of FIG. 3), stable operation can be performed without any influence on the comparison results. In addition, there may be a delay between the first and second audio signals A and B due to differences in transmission paths, etc. In this case, the output signal of the voltage comparator 6 has a delay time equivalent to that delay time. Since it appears as a short pulse, it can be removed by the subsequent third low-pass filter 7. FIG. 4 shows the voltage waveforms of the outputs d and e of the first and second Δt delay voltage comparators 3 and 5, the output f of the first voltage comparator 6, and the output g of the third low-pass filter 7. In the figure, A and C indicate periods in which the two signals are the same, and B indicates a period in which different signals are input.

Next, the third low-pass filter 7 removes the pulses due to the delay between the signals, and the signal is waveform-shaped into a rectangular shape by the second voltage comparator 8 and becomes the signal OUT.
becomes. Thus, it is possible to determine the identity of the first and second audio signals A and B based on the presence or absence of the voltage of the signal OUT.

(Effects of the Invention) As described above, in the audio signal comparison circuit of the present invention, the first audio signal is inputted and the first audio signal is detected through the first low-pass filter to detect the rising and falling edges of the signal waveform. a second Δt delay voltage comparator which receives the second audio signal and detects the rising and falling edges of the signal waveform through a second low-pass filter; A first voltage comparator that compares the voltages of both output signals of the first and second Δt delay voltage comparators, and a third voltage comparator that outputs the output of the first voltage comparator via a third low-pass filter. 2 voltage comparators, converts the audio signal into an instantaneous voltage rather than an instantaneous voltage.
Furthermore, since the high frequency components are cut out and the comparison is made based on the substantial characteristics of the rise and fall of the waveform, it is possible to perform stable comparisons without being affected by the level of the input audio signal.

Furthermore, since the voltages are compared and then the waveforms are shaped through a low-pass filter, pulses due to phase shifts and noise can be removed.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention;
FIG. 2A shows a specific circuit example of the Δt delay voltage comparators 3 and 5, FIG. It is an operation explanatory diagram. 1... Audio signal inversion circuit, 2, 4, 7... First, second, third low pass filter, 3, 5...
First and second △t delay voltage comparators, 6, 8...first and second voltage comparators, _A1 , _A2 ...operational amplifier,
C...Capacitor, _R1 , _R2 to _R4 ...Resistance.

Claims (1)

[Claims] 1 A first Δt delay voltage comparator which receives a first audio signal and detects the rising and falling edges of a signal waveform via a first low-pass filter; A second Δt delay voltage comparator detects the rise and fall of a signal waveform via a second low-pass filter, and voltage comparison between both output signals of the first and second Δt delay voltage comparators is performed. and a second voltage comparator that outputs the output of the first voltage comparator via a third low-pass filter, , an audio signal comparison circuit characterized by discriminating non-identity.