JPH0321120Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] This invention is a monaural-to-stereo conversion circuit that converts a monaural signal into a pseudo-stereo signal by connecting multiple twin T circuits with different zero point frequencies in series. Regarding.

[Prior art]

2. Description of the Related Art A circuit that pseudo-converts a monaural signal into a stereo signal by connecting a plurality of twin T circuits having different zero point frequencies in series is conventionally known. 1st
The figure shows an example of the circuit. Two twin T circuits T ₁ and T ₂ are connected in series, a monaural signal is input from input terminal 1, and a signal H is input via the twin T circuits T ₁ and T ₂ . (S) is led to the output terminal 2 as the reproduction signal of the right channel, and the subtracter 3 converts the input signal into the output signal H(S) of the twin T circuits T ₁ and T ₂ .
The signal 1-H(S) obtained by subtracting 1-H(S) is led to the output terminal 4 as a left channel reproduction signal.

FIG. 2 shows the right channel reproduction signal H(S),
This shows the frequency characteristics of the left channel reproduction signal 1-H (S), and these signals H (S), 1-H
(S) has complementary frequency characteristics. In other words, frequency components around frequencies ₁ and ₂ are mainly reproduced from the left channel, and frequencies below frequency ₁ and frequencies
Frequency components above ₂ and around the peak ′ between frequencies ₁ and ₂ are mainly reproduced from the right channel. By separating the band into the right channel and the left channel and reproducing in this way, a pseudo-stereo realistic feeling can be obtained. For example, if ₁ = 150Hz, ₂ = 4.5KHz, ′1K
Hz, bass is reproduced primarily from the left, and soprano is reproduced from the right.

However, in the circuit of FIG. 1, the output signal H(S) via the twin T circuits T ₁ and T ₂ is
As shown in FIG. 2, the two zero points mutually attenuate each other, and for example, when frequencies ₁ and ₂ are set to the above-mentioned values, the frequency decreases by about 12 dB. Also,
Therefore, from the input signal to the right channel signal H(S)
Left channel signal 1-H (S) obtained by subtracting
The peak value also deviates from 0dB. Therefore, the peak values of each channel signal H(S) and 1-H(S) are no longer aligned to 0 dB, resulting in an unbalanced band.

[Purpose of invention]

The purpose of this invention is to overcome the drawbacks of the prior art, and to provide a monaural-to-stereo conversion circuit that aligns peak values and balances the band.

[Structure of the idea]

This idea reduces the peak value by reducing the frequency characteristics outside the zero points in response to the reduction in the frequency characteristics between the zero points when multiple twin T circuits with different zero point frequencies are connected in series. This was done so that they would be aligned. That is, the low frequency side is reduced by a low frequency attenuation resistor, and the high frequency side is reduced by a high frequency attenuation filter. Then, in order to equalize the level with the input signal when subtracting, the signal is enhanced (or the input signal is lowered) by the amount of the reduction.

〔Example〕

An embodiment of this invention is shown in FIG. In this embodiment, the same reference numerals are used for parts common to the conventional circuit shown in FIG.

In FIG. 3, two twin T circuits T ₁ and T ₂ connected in series are connected to the input terminal 1.
A resistor R ₁ is installed on the output side of the twin T circuits T ₁ and T ₂ .
and a low-pass filter 5 are connected in series.
Resistor R ₁ sets the peak value in the band below frequency ₁ ,
This reduces the frequency to the peak value between frequencies ₁ and ₂ . The low-pass filter 5 lowers the peak value of the frequency band higher than frequency ₂ to the peak value between frequencies ₁ and ₂ . The signal with the peak values aligned, which is obtained via the low-frequency attenuation resistor _R1 and the low-pass filter 5, is sent to the output terminal 2 via the amplifier 6.
is guided as the right channel signal H(S). Here, the amplifier 6 is used to equalize the level of the input signal during subtraction, and to compensate for the drop in level by increasing the signal by the amount of the drop in the peak value. For example, if the decrease is -12 dB, the amplifier 6 is set to have a gain of 12 dB.

The subtracter 3 subtracts the output signal H(S) of the amplifier 6 from the signal input from the input terminal 1, and guides the subtracted value 1-H(S) to the output terminal 2 as a left channel signal. .

The configuration of the twin T circuits T ₁ and T ₂ is shown in FIG. 4.
This circuit is constructed by combining a resistor and a capacitor as shown in the figure, and its transfer characteristic is e ₀ /e _i =S ² +1/S ² +j4S+1 (S=jw/w ₀ , w=2πf, w ₀ = 1/CR). Further, Q is 1/4.

According to the circuit of FIG. 3, twin T circuits T ₁ , T ₂
As in the case of the conventional circuit, the output decreases between the two zero points, and when setting ₁ = 150 Hz and ₂ = 4.5 KHz, as shown by the solid line in Figure 5a,
It drops by about 12dB and the peak values no longer align. However, the outputs of the twin T circuits T ₁ and T ₂ pass through the low-frequency attenuation resistor R ₁ , so the frequency is reduced _{to 1.}
The following low frequency components are attenuated, and by passing through the low pass filter 5, high frequency components of frequency ₂ or higher are attenuated, so the signal output from the low pass filter 5 is shown by the dotted line in Figure 5a. As shown, the overall attenuation is -12dB, and the peak value is -12dB.
It will be aligned to . Therefore, by amplifying the output of the low-pass filter 5 by the attenuation amount of 12 dB by the amplifier 6, the peak value becomes equal to 0 dB as shown in FIG. 5b. Also, as a result, the peak value of the output signal of the subtracter 3 is also equal to 0 dB, and from the output terminals 2 and 4, the peak value of the output signal of the subtracter 3 is
As shown in the figure, the left and right channel signals H have all peak values equal to 0 dB and the bands are balanced.
(S) and 1-H(S) are obtained.

Here, an actual design example of the circuit shown in FIG. 3 is shown in FIG. The circuit in Figure 6 uses frequencies ₁ and ₂ as ₁ =
This shows the case when set to 150Hz, ₂ = 4.5KHz,
The output that has passed through the twin T circuits T ₁ and T ₂ has a characteristic that is reduced by 12 dB between the two zero points. If the low-frequency attenuation resistor R is 6.8kΩ as shown in this design example, then in the band below frequency ₁ : 6.8KΩ / 4.7KΩ x 2 + 6.2KΩ x 2 + 6.8KΩ = 0.238≒
−12dB attenuated characteristics are obtained. Further, the cut-off frequency of the low-pass filter 5 is set to approximately 15 KHz, thereby obtaining a characteristic in which the peak value is attenuated by -12 dB in the band of frequency ₂ or higher. As a result of the above, the peak value from the low-pass filter 5 is -
Characteristics that are uniform at 12dB can be obtained. The amplifier 6 is designed to have a gain of about 2 dB, and amplifies the output of the low-pass filter 5 by 12 dB, making the peak value 0 dB. , the subtracter 3 subtracts the output of the amplifier 6 from the input signal, and the peak value is complementary to the output of the amplifier 6.
Outputs a 0dB signal.

FIG. 7 shows the frequency characteristics of the left and right channel signals H(S) and 1-H(S) obtained by the circuit of FIG. 6.

〔Example〕

In the above embodiment, the case where two twin T circuits are provided is shown, but the present invention can also be applied to a case where three or more twin T circuits are provided.

In the embodiment described above, the amplifier 6 is provided on the output side of the low-pass filter 5 to amplify the signal by, for example, 12 dB. Therefore, instead of providing it at this position, it may be provided on the input signal input side of the subtracter 3 to attenuate the input signal by, for example, 12 dB.

[Effect of idea]

As explained above, according to this invention, in a monaural-to-stereo conversion circuit in which a plurality of twin T circuits having different zero point frequencies are connected in series, in response to the attenuation of the frequency characteristics between the zero points, By attenuating the frequency characteristics, the peak values of the signals of one channel are aligned, and the level of that signal and the level of the input signal are aligned with the amplifier and subtraction is performed, so that all the peak values are aligned. characteristics, and a good band balance can be obtained.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing a conventional monaural-to-stereo conversion circuit, Figure 2 is a diagram showing the frequency characteristics of the output signal from the circuit in Figure 1, and Figure 3 is a diagram showing an embodiment of this invention. Figure 4 is a circuit diagram showing the configuration of the twin T, Figure 5 is an explanatory diagram of the operation of the circuit in Figure 3, Figure 6 is a circuit diagram showing an actual design example of the circuit in Figure 3, and Figure 7 is a circuit diagram showing the configuration of the twin T. This figure is a circuit diagram showing the frequency characteristics of the output signal by the circuit of FIG. 6. 1...Input terminal, 2...Right channel output terminal, 3...Subtractor, 4...Left channel output terminal, 5...Low pass filter, 6...Amplifier,
T ₁ , T ₂ ... Twin T, R ₁ ... Low frequency attenuation resistor.

Claims (1)

[Scope of utility model registration request] A plurality of twin T circuits with different zero point frequencies are connected in series, a monaural signal is inputted, the output is outputted as a signal of one stereo channel, and a subtracter extracts the signal of the one channel from the monaural signal. In a monaural-to-stereo conversion circuit that outputs the subtracted output as a signal of the other stereo channel, the cascade-connected twin T
A low-frequency attenuation resistor and a high-frequency attenuation filter are interposed on the output side of the circuit, and the cascade-connected twin T
The level peak values of each frequency band divided by the zero point frequency of the frequency-level characteristic in the output signal of the circuit are made equal, and the level of the signal with the equal level peak values and the level of the monaural signal are made equal with the level of the monaural signal. A monaural-to-stereo conversion circuit characterized in that input is input to a subtracter.