JPS601571A - Audio signal comparing circuit - Google Patents

Abstract

PURPOSE:To determine the identity of two audio signals at a sufficient accuracy with a simple construction by comparing and determining results of the comparison of delayed voltages for detecting the rising and falling of signal waveforms. CONSTITUTION:When a need arises to match the audio signal in the polarity as inputted from the terminal B, the audio signal inputted from the terminal A is inverted with a voice signal inversion circuit 1 and processed with a DELTAt delay voltage comparator 3 which compares the signal with the other input thereof delayed by the time DELTAt through a capacitor or the like by way of an LPF2. The audio signal inputted from the terminal B is likewise processed with an LPF4 and a DELTAt delay voltage comparator 5. The comparison pulses corresponding to the rising and the falling of a waveform based on variations with the time DELTAt of the respective audio signals from the comparators 3 and 5 are compared with a voltage comparator 6 and when both the signals coincide, the output of the comparator 6 becomes zero. Thus, with a simple construction, the identity of the audio signals is determined at a sufficient accuracy with a stable comparison depending on the rising and the falling of the waveform.

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, two signals are directly compared using a voltage comparator using a differential amplifier such as an operational amplifier, and based on the result, it is determined whether the audio signals are the same or different.
However, since this type of method directly compares the instantaneous voltages of the signals, the levels of the two audio signals must be adjusted within a range that can be considered sufficiently equal compared to the evils of voltage comparators. Must be. 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 very difficult but also uncommon to manage them to the same level.

Furthermore, if a delay occurs between two audio signals due to a difference in transmission path, etc., there is a disadvantage that the comparison output will show a difference even though the exact same signal is input.

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

(Objective of the Invention) The present invention has been proposed in view of the above points, and has a simple configuration and is capable of detecting the sameness of two audio signals with sufficient accuracy.
It is an object of the present invention to provide an audio signal comparison circuit that can determine whether the signals are different or not.

(Configuration of the Invention) FIG. 1 is a configuration block diagram showing an embodiment of the present invention. In the figure, A and B indicate two audio signals to be compared, and one signal A is selected by a changeover switch SW to be passed through the audio signal inverting circuit 1 or directly applied to the low-pass filter 2. The signal B is directly input to the low-pass filter 4. Here, the audio signal inversion circuit 1 is provided because 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, etc. This is to check the polarity of the signal and set the changeover switch SW in advance.

In addition, the low-pass filter 2.4 is provided to cut out high frequency components within a range that allows recognition of the sameness of the audio signals and to facilitate comparison.
A low-pass filter of +2) is used.

Then, the output signal of the low-pass filter 2.4 is inputted to the delayed voltage comparator 3.5, and the output signal of the delayed voltage comparator 3.5 is inputted to the voltage comparator 6, 6 is followed by a low-pass filter 7 and a voltage comparator 8.
are connected in sequence and the output OUT is taken out. Here, the delay voltage comparator 3.5 determines the rising and falling edges of the input signal waveform and outputs a high-level or low-level signal.For example, it has a configuration as shown in FIG. 2 (A). be done. In FIG. 2(a), the input signal is divided into two paths by resistors R1 and R2, one end of resistor R1 is connected to the inverting input terminal of operational amplifier A1, and one end of resistor R2 is connected to the non-inverting input terminal. Further, a capacitor C is connected between the non-inverting input terminal of the operational amplifier A1 and ground. Figure 2 (b) shows the voltage waveforms at the points shown in Figure 2 (a), that is, at both input terminals and output terminal of operational amplifier A+, and the voltage waveform at point b is due to the delay effect of capacitor C. Therefore, the voltage change at point a is delayed by Δt in time. Here, the delay time Δt is set sufficiently short with respect to the period of the audio signal, and the operational amplifier A determines the magnitude relationship between the input audio signal and the signal obtained by delaying this audio signal. This converts changes in the audio signal within a minute time, that is, changes in the signal such as the rise and fall of the signal waveform, into a signal that characterizes the change. That is, the second
In the figure (b), during the rising period when signal a rises with time, the signal l delayed by Δt is always at a lower voltage than the original signal a, and during the falling period when signal a falls with time. Since the signal is always at a higher voltage than the original signal, the rainy period can be easily determined from the magnitude relationship of the voltage. Therefore, the 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 of the signal can be characterized. Note that the polarity of the input terminal of operational amplifier A1 is the second
It is not limited to the one shown in Figure (a), 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 voltage comparator 6 in FIG.
Points E and E are connected to the inverting input terminal and non-inverting input terminal of operational amplifier A2 through resistors R3 and R4, respectively, and a resistor Rs is connected between the inverting input terminal and the output terminal, and a resistor Rs is connected between the non-inverting input terminal and the ground. A resistor R6 is connected to each. 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. First, the following relationship is required: Rs R6 R3R4. For example, R3=R4=R5=Rs
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.

Hereinafter, the operation of comparing audio signals will be explained using the embodiment shown in FIG. Now, of the audio signals A and B to be determined as being the same or different, the signal @A is input directly or inverted to the low-pass filter 2 by operating the changeover switch SW, and the signal B is directly input to the low-pass filter 4. is input. The low-pass filters 2 and 4 cut high frequency components contained in the signals A and B, and provide the output signal Δ to a delayed voltage comparator 3.5. The delay voltage comparator 3.5 outputs a low level or high level signal according to the rising and falling periods of the signal liquid sent from the low-pass filter 2.4. Converts into a pulse-like signal that characterizes waveform changes. Therefore, the input J
-ru audio No. 45 △.

It is completely unaffected by the amplitude level of B.
Therefore, audio signals detected from arbitrary points can be compared.

Next, the voltage comparator 6 compares Δ with the output signal of the delayed voltage comparator 3゜5, and when both are high level or low level, the output becomes zero, and when both are different from each other, the output signal is low level or low level. Outputs a high level signal. In other words, if the audio signals A and B are the same, the pulse signals sent from the delay voltage comparator 3.5 will be the same, so the output of the voltage comparator 6 will be zero, and the difference will be different. If it is a signal, positive and negative signals will be output irregularly. Note that when comparing voltages, external noise and voltage fluctuations due to various elements are considered, but since the signal input to the voltage comparator 6 is a signal saturated at a low level or a high level, the sensitivity of the voltage comparator 6 can be set sufficiently low (gain 1 in the example of FIG. 3), so stable operation can be performed without any influence on the comparison results. Also, audio signal A.

There may be a delay between B and B due to differences in transmission paths, etc. In this case, the output signal of the voltage comparator 6 appears as a short pulse corresponding to the delay time, so the subsequent low-pass It can be removed by filter 7. Figure 4 shows Δ as the output d of the delayed voltage comparators 3 and 5.
, e shows the voltage waveforms of the output f of the voltage comparator 6 and the output q of the low-pass filter 7, where (a) and (c) show the period when the two signals are the same, and (b) shows the period when the two signals are different. Indicates the period of time during which it has been suspended.

Next, a low-pass filter 7 filters the signals based on the delay between the signals (
The signal from which the pulses have been removed is shaped into a rectangular waveform by the voltage comparator 8 and becomes a signal 0υ. Therefore, it is possible to determine the identity of the audio signals A and B based on the presence or absence of the voltage of the signal 0tlT.

(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 Δ which detects the rising and falling edges of the signal waveform is connected to the delayed voltage comparator. and a second Δ which inputs a second audio signal and detects the rise and fall of the signal waveform, and a delay voltage comparator, and the first and second Δ are both output terminals of the delay voltage comparator. It is equipped with a voltage comparator that compares the voltages of the audio signals, and compares the audio signals not by the instantaneous voltage but by the substantial characteristics of the rise and fall of the waveform, so there is no influence on the level of the input audio signal. This has the effect of allowing stable comparisons to be made without any influence.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 (
A) is a specific circuit example of the Δtill voltage comparator 3.5,
3 is a specific circuit example of the voltage comparator 6, and FIG. 4 is an explanatory diagram of the operation of FIG. 1. 1. Audio signal inversion circuit; 2. 4.7...Low pass filter, 3.5...Δ delayed voltage comparator, 6
．． 8... Voltage comparator, A+, A2... operational amplifier, C... capacitor, R+, R2, ~, R6
°. ...Resistance Figure 1 448- Figure 3 5 / Figure 4

Claims (1)

[Claims] A first Δtl voltage comparator that receives the first audio signal and detects the rising and falling edges of the signal waveform.A first Δtl voltage comparator that receives the second audio signal and detects the rising and falling edges of the signal waveform. 2 Δtill extended voltage comparators, and a voltage comparator for comparing the voltages of both river force signals of the first and second Δ delayed voltage comparators;
An audio signal comparison circuit for determining whether second audio signals are the same or different.