JPH0125280B2 - - Google Patents

Description

[Detailed Description of the Invention] Stereo broadcasting of television broadcast audio has become popular, and in response to this, television sets equipped with two speakers are becoming standard. Efforts have been made to create a stereo effect.

FIG. 1 shows an example of such a stereo conversion circuit, in which 1 is a stereo demodulation circuit for a television set;
L and 1R are output terminals for the left and right channels, and stereo left and right channel audio signals are taken out from these terminals 1L and 1R during stereo broadcasting, and monaural audio signals are taken out during monaural broadcasting.

In addition, 2 is a delay circuit for slightly delaying the audio signal to give a stereo feeling, 3L, 3
R is a subtraction circuit, 4L and 4R are high-pass filters,
5L and 5R are amplifiers, and 6L and 6R are left and right speakers. Note that when the delay amount of the delay circuit 2 is large, the circuits 3L and 3R may be adder circuits.

In this way, a delay circuit is generally used to convert a monaural signal into stereo. However, with these stereo conversion circuits, although the stereo effect is great for music and sound effects, it may not always be possible to obtain a satisfactory stereo effect for programs that mainly consist of audio, such as news programs, depending on the user's preference. There were many.

This invention attempts to solve these problems.

First, an example of a filter circuit that can be used in the present invention will be explained.

In FIG. 2, 10 indicates the filter circuit as a whole, 10A indicates the variable gain amplifier, 1
1 and 12 are first and second input signal sources.

In this case, in this example, the amplifier 10A is constituted by two sets of differential amplifiers and a current mirror circuit serving as their constant current source, and the emitters of transistors Q ₁ and Q ₂ are connected to resistors R ₂ and R _{3 .} ( _R2 = _R3 )
The collectors of transistors Q _{1 and} Q ₂ are connected to the emitters of load transistors Q ₄ and Q ₅ to form a first differential amplifier. ,
The emitters of transistors Q ₆ and Q ₇ are connected to the collector of transistor Q ₈ for constant current source, the bases of transistors Q ₆ and Q ₇ are connected to the collectors of transistors Q ₁ and Q ₂ , and the collector of transistor Q 6 is connected to the collector of transistor Q ₈ for constant current source. It is connected to the power supply terminal T ₄ , and the collector of the transistor Q ₇ is connected to the terminal T ₄ through a resistor R ₄ to form a second differential amplifier.

Further, a transistor _Q13 is connected to the transistor _Q3 to form a first current mirror circuit, and the base and collector of the transistor _Q13 are connected to the terminal _T4 through a resistor _R5 . Further, a transistor _Q18 is connected to the transistor _Q8 to form a second current mirror circuit, and the base and collector of the transistor _Q18 are connected to the resistor _R6.
connected to terminal T ₄ through.

Furthermore, the first input terminal T ₁ and the transistor Q ₁
A resistor R ₁ is connected between the base of the transistor Q 1 and the second input terminal T ₂ is connected to the base of the transistor Q ₂ , and the collector of the transistor Q ₇ is connected to the transistor Q through the emitter follower transistor Q ₉ and the capacitor C ₁ . ₁ and the output terminal T ₃ is connected to this connection point.

In such a configuration, for simplicity, the terminal
Suppose T ₂ is grounded. In this state, when a signal S ₁ (including the base bias voltage) is supplied from the signal source 11 to the base of the transistor Q ₁ , this signal S ₁ is converted into a differential signal by the transistors Q ₁ and Q ₂ in the amplifier 10A. The signal is amplified, further differentially amplified by transistors Q ₆ and Q ₇ , and taken out to the emitter of transistor Q ₉ . Therefore,
The circuit 10 of FIG. 1 can be equivalently shown as shown in FIG. 3A, in which a capacitor C ₁ is connected in parallel between the input end and the output end of the amplifier 10A.

And like this, capacitor C ₁ is connected to amplifier 1
When connected to 0A, due to the Miller effect, the capacitance C when looking from the resistor _R1 to the amplifier 10A side is: C=C ₁ A A: Gain of amplifier 10A (A≫1), as shown in Figure 3A. The circuit is further shown in FIG. 3B. Therefore, the circuit 10 of FIG. 2 functions as a low-pass filter, and a low-pass output is taken out at terminal _T3 . Further, the cutoff frequency _c of this low-pass output is _c = 1/2πC ₁ AR ₁ . . . (i).

In this case, the gain A of the amplifier 10A is A=R ₄ /2R ₂ I ₈ /I ₃ I ₃ : Collector current of transistor Q ₃ I ₈ : Collector current of transistor Q ₈ , so equation (i) is obtained. _c = 1/2πC ₁ R ₁ 2R ₂ /R ₄ I ₃ /I ₈ ...(ii).

Furthermore, since transistors Q ₃ and Q ₁₃ constitute a current mirror circuit, the collector current I ₃ of transistor Q ₃ is equal to the collector current of transistor Q ₁₃ , and therefore I ₃ = V _CC /R ₅ . , Similarly, since I ₈ = V _CC /R ₆ , the cutoff frequency _c is obtained from equation (ii) as follows: _c = 1/2πC ₁ R ₁ 2R ₂ /R ₄ V _CC /R ₅ R ₆ /V _CC = 1 /πC ₁ R ₂ /R ₄ R ₆ /R ₁ 1/R ₅ ...(iii).

On the other hand, if _the terminal T ₁ is grounded and the signal S ₂ is supplied to the terminal T ₂ , this circuit 10 is equivalently shown as shown in _FIG . The function H(ω) is H(ω) = Vout/Vin = R ₁ /R ₁ (1+1/A) + 1/jωC ₁ A = R ₁ /R ₁ +1/jωC ₁ A, which is shown in Fig. 4. This is equivalent to the characteristics of the high-pass filter shown in B. Therefore, in this case, the circuit 10 functions as a high-pass filter whose cutoff frequency _c is also expressed by equation (iii).

Therefore, as shown in FIG. 2, when signals S ₁ and S ₂ are simultaneously supplied to this filter circuit 10, the equivalent circuit becomes as shown in _FIG . It functions as a low-pass filter and also as a high-pass filter for the signal _S2 , and the frequency characteristics for the signals _S1 and _S2 are as shown in FIG.

In the present invention, for example, the filter circuit 10 is used to perform stereo conversion, and the stereo feeling or spread can be continuously changed.

An example of this will be explained below.

In FIG. 7, 10L and 10R indicate filter circuits, which are configured similarly to the above-mentioned filter circuit 10, but with transistor _Q13 and resistor
_R5 is common to filter circuits 10L and 10R, and resistor _R5 is a variable resistor.

The output signal of the terminal 1L of the stereo demodulation circuit 1 is supplied to the terminal _T1 of the filter circuit 10L, and is also supplied to the terminal _T2 of the filter circuit 10L through the delay circuit 2L. Also, the output signal of the terminal 1R of the demodulation circuit 1 is transmitted to the filter circuit 10R.
The signal is supplied to the terminal T ₂ of the filter circuit 10R, and is also supplied to the terminal T ₁ of the filter circuit 10R through the delay circuit 2R. And the terminals of the filter circuits 10L and 10R
The output signals of T ₃ and T ₃ are supplied to amplifiers 5L and 5R. Note that the delay circuits 2L and 2R are similar to the delay circuit 2 in FIG.

In such a configuration, if the variable resistor R ₅ is made small, the filter circuit 10 can be calculated from equation (iii).
The cutoff frequency _c of L and 10R becomes high, for example, can be set above the audible band. Therefore,
In this case, considering the audible band, the signals at terminals T ₁ and T ₁ of filter circuits 10L and 10R are
T ₃ , T ₃ are taken out as is, but terminals T ₂ , T ₂
Since the signal is no longer taken out to terminals T ₃ and T ₃ , the output signal of terminal 1L of demodulation circuit 1 is
L → terminal T ₁ → filter circuit 10L → terminal T ₃ → amplifier 5L is supplied to amplifier 5L through the line, and the output signal of terminal 1R is supplied to terminal 1R → delay circuit 2R → terminal T ₁ → filter circuit 10R → terminal T ₃ → Amplifier 5R through the amplifier 5R line
supplied to Therefore, in this case, the audio signal supplied to the speaker 6R is the same as the audio signal supplied to the speaker 6L, with only a slight delay, so at this time, the reproduction is almost monaural, and the sound is transmitted to the speaker 6L. 6L, 6R
The image is positioned approximately in the center of the image.

However, if the variable resistor _R5 is increased,
From equation (iii), the cutoff frequency _c of the filter circuits 10L and 10R becomes low and falls within the audible band. Therefore, in this case, in the filter circuit 10L, the low frequency component of the audio signal from the terminal 1L and the delayed high frequency component are mixed and taken out to the terminal _T3 , and in the filter circuit 10R, the low frequency component of the audio signal from the terminal 1L is mixed and taken out from the terminal 1R. The high-frequency components of the audio signal and the delayed low-frequency components are mixed and output to terminal _T3 . Therefore, in this case, the speakers 6L and 6R
Since audio signals having a time difference and different frequency components are supplied, similar to the apparatus shown in FIG. 1, sound with a stereophonic or spacious sound is reproduced.

At that time, the cutoff frequency _c of the filter circuits 10L and 10R is set by the variable resistor _R5 .
This allows the stereo feel or spread of the reproduced sound to be changed arbitrarily and continuously.

In this way, according to this invention, by adjusting the variable resistor _R5 , the user can perform playback with a desired stereo effect or spread, and can therefore achieve satisfactory stereo sound even in programs centered on audio such as news. You can feel it.

Furthermore, similar effects can be obtained during stereo broadcasting.

FIG. 8 shows another example of the filter circuit 10, in which the resistor R ₁ is divided into resistors R ₁₁ and R ₁₂ , and the terminal T ₃ is connected to the midpoint of the connection. . Therefore, this filter circuit 10 is equivalently as shown in FIG. 9, and for the signal _S1 , the first
As shown in Figure 0, it works as a high-frequency attenuation filter.

Therefore, even if this filter circuit 10 is used,
After all, you can get a stereo feeling or spread, and you can change the size freely.

[Brief explanation of drawings]

1, 2 to 6, and 8 to 10 are explanatory diagrams of this invention, and FIG. 7 is a system diagram of an example of this invention. 1 is a stereo demodulation circuit, and 2L and 2R are delay circuits.

Claims (1)

[Claims] 1. Each of the two audio signal lines is divided into a first and a second signal line, and is again coupled to the original signal line, and each of the two audio signal lines is connected to the divided first signal line. A high-pass filter is provided, and a delay circuit is connected in series to the high-pass filter in a first signal line of at least one of the two audio signal lines, and continuously changes the cutoff frequency of the high-pass filter. A sound image control circuit that continuously changes the stereo feeling or spread of a reproduced sound image.