JPS6249765B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transmission frequency characteristic correction device for correcting, in an audio reproduction system, changes in the bass range due to differences in the installation positions of speakers in a listening room.

In general, the transmission frequency characteristics of speakers in a listening room vary depending on the volume of the room, the type of interior materials, the installation position of the speakers, the listening position, and the like. The degree of this change tends to be small in the mid-high range and large in the low range. A characteristic of this change is that large peaks or dips tend to occur within the band of approximately 100 to 400 Hz. As an example, FIG. 1 shows changes in transmission frequency characteristics due to differences in speaker installation positions in a listening room of approximately 6 tatami mats. According to this, it can be seen that different peaks or dips occur depending on the speaker installation positions S ₁ to _{S 9} . In such a case, although sound is being emitted at a uniform level from the speaker, a feeling of excess or deficiency of low temperature occurs at the listening position.

Conventionally, the following remedies have been used to solve this problem, but all of them have practical drawbacks.

(1) How to change the speaker installation position.

This is the simplest method and is also effective in terms of acoustic theory. However, in listening rooms in Japan, where the room volume is small and is often equipped with furniture and fixtures, it is difficult to secure the optimal installation position for the speakers, and this is not necessarily highly practical.

(2) How to eliminate harmful reflected sounds.

It is possible to remove acoustically harmful reflected sounds by applying sound absorption treatment to walls where reflected sounds that cause harmful level changes in the frequency characteristics of the bass range occur. However, this method is often not applicable to listening rooms in ordinary homes.

(3) Method using a graphic equalizer.

A typical graphic equalizer allows level adjustment in 1/3 to 1/1 octave bands. Therefore, there are various uses other than correcting the level of the bass range. However, they are more expensive than audio equipment and are rarely used in general households.

(4) Method using tone control.

Generally, tone control devices built into audio equipment have a frequency range below or above a certain cutoff frequency, as shown in Figure 2.
It is designed to adjust the level increase/decrease with a nearly constant slope. Therefore, the peak on the transmission frequency characteristic in a general listening room,
It is not possible to correct for dips.

The present invention has been made in view of the above, and operates as a peak/dip filter within a certain frequency band, and furthermore, the center frequency of the peak/dip,
It is an object of the present invention to provide a transmission frequency characteristic correction device that can independently vary three parameters, level and bandwidth, with a simple circuit configuration.

The present invention will be explained below using examples.

FIG. 3 is a block diagram of one embodiment of the present invention.

This embodiment includes an all-pass type variable phase shift circuit 1 whose phase changes monotonically from 0 to -2π radians as the frequency of an input signal increases, and whose phase change gradient is variable; 1, a subtracter 10 that subtracts the output signal of the variable attenuator 8 from the input signal, and a subtracter 10 that subtracts the output signal of the variable attenuator 8 from the output signal of the variable attenuator 9. and an adder 11 that adds the output signal of the adder 10 and the output signal of the subtracter 12, and adds the output signal of the adder 10 to the variable phase shift circuit 1.
and the output signal of adder 11 is input to the output terminal.
It is configured to be taken out from OUT.

Further, the variable phase shift circuit 1 is connected in cascade and receives as input the input signal to the first phase shift circuits 2 and 3, both of which have a transfer function of (1-jωT)/(1+jωT), and the variable phase shift circuit 1. A variable attenuator 5 receives the output signal of the variable phase shift circuit 1 and operates in conjunction with the variable attenuator 4 and has the same attenuation ratio. A subtracter 6 subtracts the output signal of the variable attenuator 5 and outputs an input to the primary phase shift circuit 2, and adds the output signal of the primary phase shift circuit 3 and the output signal of the variable attenuator 4 to obtain an output signal. Adder 7 for output signal of variable phase shift circuit 1
It is made up of. Here, IN is an input terminal of the transmission frequency characteristic correction device, and OUT is an output terminal of the transmission frequency characteristic correction device.

Further, ω is the angular frequency of the input signal of the transmission frequency characteristic correction device, and T is the time constant of the primary phase shift circuits 2 and 3. Further, the angular frequency ω of the input signal is the same as the angular frequency of the input signal of the variable phase shift circuit 1.

Next, before explaining the operation of this embodiment configured as described above, the principle of this embodiment will be explained.

FIG. 4 is a block diagram for explaining the principle of the present invention, and the subtracter 1 in the block diagram shown in FIG.
2, the loop from the variable attenuator 8 to the subtracter 12 is omitted.

The output signal of the variable attenuator 8 is subtracted by the subtracter 10 from the input signal applied to the input terminal IN, and the output signal of the subtracter 10 is input to the variable phase shift circuit 1, and the output signal of the variable phase shift circuit 1 is is input to the variable attenuator 8 and the variable attenuator 9, and the output signal of the subtracter 10 and the output signal of the variable attenuator 9 are input to the adder 1.
The configuration is such that the signal added by 1 is taken out from the output terminal OUT.

In the circuit shown in Figure 4, the input signal applied to the input terminal IN causes phase interference with the signal that has passed through the variable phase shift circuit 1, and the level changes in the band centered on the frequency where the phase changes by -π radians. It is emphasized or suppressed, producing peaks and dips.

Therefore _, when the gain of the variable attenuator 8 is g ₁ and the gain of the variable attenuator ₉ is g ₂ , as shown in FIG. When ₁ <gain g ₂ , a dip characteristic is exhibited, and its level is determined depending on the gain difference (g ₁ to _{g 2} ).

Furthermore, when the slope of the phase change of the variable phase shift circuit 1 changes, the bandwidth of the peak and dip changes as shown in Fig. 5b, and the larger the slope of the phase change, the narrower the bandwidth of the peak and dip. Become.

Next, the operation of the transmission frequency characteristic correcting device according to the embodiment of the present invention shown in FIG. 3 will be explained.

One embodiment of the present invention uses the operating principle of the block diagram of FIG. 4 explained above.
The transfer function R(jω) of the variable phase shift circuit 1 is expressed by equation (1).

R(jω) = (1+g ₀ )(1-ω ² T ² )-j2ωT(1-g ₀
)/(1+g ₀ )(1-ω ² T ² )+j2ωT(1-g
₀ )...(1) Since the numerator and denominator of equation (1) are mutually conjugate, the amplitude term |R(jω)| is 1. This indicates that the variable phase shift circuit 1 is an all-pass type circuit.

Next, the phase term (ω) and its derivative d/
dω is (ω)=-2tan ^-1 2(1-g ₀ )ωT/(1+g ₀ )
(1- ^ω2T2 )...(2) d/dω= ^-4 (1+ _g0 )(1- _g0 )(1+ ^ω2
T ² )T/(1+g ₀ ) ² (1-ω ² T ² )+4(1-
g ₀ ) ² ω ² T ² (3). Here g ₀ is the gain of variable attenuators 4 and 5.

The following equation (4) is derived from equations (2) and (3).

Therefore, from equation (4), the phase characteristics of the variable phase shift circuit 1 are as follows: (1) The phase monotonically decreases from 0 to -2π radians as the input signal increases.

(2) The phase rotates by exactly -π radians when the angular frequency ω becomes the reciprocal of the time constant T.

(3) The slope of the phase change is determined depending on the gain g ₀ of the variable attenuators 4 and 5, and the slope becomes steeper as the gain g ₀ becomes larger.

Therefore, _the transfer function S(jω) of the transmission frequency characteristic correction device of this embodiment shown in _{FIG .} )(1- ^{ω2T2 )} +2jωT(1- _g0 )(1+ _g1 - _g2 ) B=(1+ _g0 )(1+ _g1 )(1- ^{ω2T2 )} +2jωT(1- _g0 ) (1-g ₁ ).

Here, the amplitude term of the transfer function S(jω) |S(j
ω) | is |S(jω)|=√ …(6) However, C=(1−g ₀ ) ² (1−g ₁ +g ₂ ) ² (1−ω ² T ² ) ² + 4(1− g ₀ ) ² (1+g ₁ -g ₂ ) ² ω ² T ² D=(1+g ₀ ) ² (1+g ₁ ) ² (1-ω ² T ² ) ² + 4(1-g ₀ ) ² (1-g ₁ ) ² ω ² T ² .

From equation (6), the graph of the amplitude term |S(jω)| is ω=
It shows a peak characteristic or a dip characteristic having a local maximum value or a local minimum value at 1/T, indicating that this transmission frequency characteristic correction device is a peak/dip filter. Furthermore, if the peak characteristics and dip characteristics are shown on a logarithmic scale with the horizontal axis, they are symmetrical.

That is, the amplitude transmission frequency characteristic of this embodiment is a symmetrical peak or dip characteristic, and the angular frequency of the axis of symmetry is given by the reciprocal of the time constant T, 1/T.

Also, the peak and dip level L
(dB) is L(dB)=20log(1+g ₁ -g ₂ )(1+g ₁ )/(
1-g ₁ )(1-g ₁ +g ₂ )...(7) The height of the peak or the depth of the dip can be determined by fixing the gain g ₂ of the variable attenuator 9.
When _{g 1 >} g ₂ /2, it exhibits a peak characteristic, and when g ₁ < g ₂ /2, it exhibits a dip characteristic.

Further, the smaller the gain g ₁ is, the deeper the dip is, and within the range of g ₁ < g ₂ , the larger the gain g ₁ is, the higher the peak height is.

The gain _g2 of the variable attenuator 9 defines the upper and lower limit values of the peak and dip, and is usually conveniently set to an appropriate value.

Next, the gains _g0 of variable attenuators 4 and 5 define the peak and dip bandwidths (or Q),
As the value of gain g ₀ increases in the range of g ₀ <1, the bandwidth decreases.

From the above explanation, the characteristics of the transmission frequency characteristic correction device of this embodiment are as follows.

(1) When the horizontal axis is plotted on a logarithmic scale, the amplitude frequency characteristics show symmetrical peak and dip characteristics, and ω
It reaches a maximum or minimum at an angular frequency of =1/T. Therefore, the center frequencies of the peak and dip can be set by changing the time constant T of the variable phase shift circuit 1.

(2) The maximum value of the peak and the minimum value of the dip are determined using the variable attenuator 8 while fixing the gain _g2 of the variable attenuator 9.
The gain g can be set independently by changing ₁ . For example, when the gain g ₂ is set to 0.7 and the gain g ₀ is set to 0, the peak and dip levels change as shown in FIG.

(3) The bandwidths of the peak characteristics and dip characteristics can be set independently by changing only the gains g ₀ of the variable attenuators 4 and 5. FIG. 7 shows an example of the peak characteristic when the bandwidth of the peak characteristic is changed with the gain g ₁ =0.7.

Next, a specific circuit will be explained.

FIG. 8 is a circuit diagram showing an example of a specific circuit configuration of the embodiment of the present invention shown in FIG. 3.

In Figure 8, OP ₁ , OP ₂ , OP ₃ , OP ₄ , OP ₅
is a buffer amplifier consisting of a voltage follower,
Operational amplifier OP ₆ , capacitor C ₁ and variable resistor r ₃
constitutes the primary phase shift circuit 2, and the operational amplifier OP7,
A variable resistor r ₄ operating in conjunction with a capacitor C ₂ and a variable resistor r ₃ constitutes a primary phase shift circuit 3 .
Also, resistor r ₁ and variable resistor r ₂ connect variable attenuator 4 to resistor r 1 and variable resistor r 2.
A variable resistor r6 operating in conjunction with _r5 and variable resistor _r2 constitutes a variable attenuator 5, _OP8 is _an operational amplifier constituting a subtracter 6, and _OP9 is an operational amplifier constituting an adder 7. It's an amplifier. Further, the resistor r ₇ and the variable resistor r ₈ constitute a variable attenuator 8, and the resistor r ₉ and the resistor r ₁₀ constitute a variable attenuator 9, but in this case, the gain g ₂ is fixed. Further, OP ₁₀ is an operational amplifier forming the attenuator 10 , OP ₁₁ is an operational amplifier forming the adder 11 , and OP ₁₂ is an operational amplifier forming the subtracter 12 .

Now, the resistance value between the output terminal of OP ₅ and the non-inverting input terminal of OP ₂ , the resistance value between the non-inverting input terminal of OP ₂ and ground, and the resistance value between the output terminal of OP ₉ and the non-inverting input terminal of OP ₄ . resistance between the non-inverting input terminal of OP ₄ and ground, the resistance between the output terminal of OP ₉ and the non-inverting input terminal of OP ₃ , and the resistance between the non-inverting input terminal of OP ₃ and ground. The resistance values between R ₁ , R ₂ , R ₅ , R ₆ ,
Let R ₇ and R ₈ and further resistors r ₃ , r ₄ , r ₉ and r ₁₀
Let the resistance values of R ₃ , R ₄ , R ₉ and R ₁₀ respectively,
If the capacitances of capacitors C ₁ and C ₂ are C ₁ and C ₂ ,
Each constant is _R1 / _R2 = _R5 / _R6 =1- _g0 / _g0 , _C1 = _C2 , _R3
= _R4 , _R7 / _R8 =1- _g1 / _g1 , _R9 / _R10 =2- _g2
/ _g2 .

Therefore, the circuit shown in FIG. 8 has a one-to-one correspondence with each block in the block diagram of this embodiment shown in FIG. Therefore, its operation is exactly the same as that described using FIG. 3.

Note that variable resistors r ₃ and r ₄ are variable resistors that set the time constant of the variable phase shift circuit.

Next, a method of using the transmission frequency characteristic correction device of the present invention will be explained.

FIG. 9 is a diagram showing an example of this method of use.

13 is a record player, tape recorder,
A sound source device such as an FM tuner, 14 a preamplifier including an RIAA characteristic equalizer, 15 a transmission frequency characteristic correction device according to the present invention, 16 a main amplifier, and 17 a speaker.

As described above, the transmission frequency characteristic correction device 15 connected between the preamplifier 14 and the main amplifier 16 operates as a peak or dip filter within a certain frequency band, for example, 100 to 400 Hz, and the center of the peak or dip. Frequency, level and its bandwidth can be set independently. Therefore, for example, if the transmission frequency characteristic during reproduction by the speaker 17 has a large level peak in the bass range, as shown in _S1 shown in FIG. The peak can be removed by setting it to act as an approximate dip filter.

Similarly, when a dip occurs in the transmission frequency characteristic as shown in _B9 of FIG. 1, the dip is removed by setting the transmission frequency characteristic correction device 15 to act as a peak filter. be able to.

As explained above, according to the present invention, it operates as a peak/dip filter within a certain frequency band, and the center frequency of the peak/dip,
The three parameters of level and bandwidth can be set independently, and the circuit configuration for this purpose is also simple.

Therefore, it can be constructed at a lower cost than a graphic equalizer, and can be built into an audio device.

Furthermore, by cascading a plurality of transmission frequency characteristic correction devices of the present invention, fine correction can be performed in response to more complex changes in transmission frequency characteristics.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing changes in transmission frequency characteristics due to differences in speaker installation positions. Figure 2 is a characteristic diagram of the tone control device. FIG. 3 is a block diagram of one embodiment of the present invention. FIG. 4 is a block diagram for explaining the principle of an embodiment of the present invention. Figure 5 a and b
4 is a characteristic diagram for explaining the operation of the block diagram in FIG. 4. FIG. FIG. 6 and FIG. 7 are diagrams for explaining the operation of one embodiment of the present invention. FIG. 8 is a specific circuit diagram of an embodiment of the present invention. FIG. 9 is a block diagram showing an example of use of the transmission frequency characteristic correction device of the present invention. 1... variable phase shift circuit, 2 and 3... primary phase shift circuit, 4, 5, 8 and 9... variable attenuator, 6,
10 and 12...subtractor, 7 and 11...adder.

Claims (1)

[Claims] 1. The phase becomes 0 as the frequency of the input signal increases.
an all-pass type variable phase shift circuit that monotonically changes up to -2π radians and has a variable gradient of phase change;
first and second variable attenuators that receive the output signal of the variable phase shift circuit as input; and a first subtracter that subtracts the output signal of the first variable attenuator from the input signal applied to the input terminal. , a second subtractor for subtracting the output signal of the first variable attenuator from the output signal of the second variable attenuator, and adding the output signal of the first subtractor and the output signal of the second subtractor. a first adder, the output signal of the first subtracter is used as an input signal of a variable phase shift circuit, and the output signal of the first adder is used as an output. . 2. The variable phase shift circuit includes first and second cascaded primary phase shift circuits whose time constants change in conjunction with each other, and third and second primary phase shift circuits whose attenuation rates can change to the same attenuation rate in conjunction with each other. a fourth variable attenuator; a third subtracter that subtracts the output signal of the fourth variable attenuator from the input signal of the variable phase shift circuit; and a second adder that adds the output signal of the attenuator, the output signal of the third subtracter is used as the input signal of the first primary phase shift circuit, and the output signal of the second adder is used as the input signal of the first primary phase shift circuit. Claim 1 characterized in that the input signal of the variable phase shift circuit is used as the input signal of the fourth variable attenuator and the output signal of the variable phase shift circuit, and the input signal of the variable phase shift circuit is used as the input signal of the third variable attenuator. Transmission frequency characteristic correction device as described in 2.