JPS6325772Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a loudness control circuit for a TV receiver or the like that uses an IC for audio signal processing.

The volume of sound that humans perceive (loudness) is not necessarily constant in relation to the absolute sound intensity.
It is known to be a function of sound intensity and frequency. If this fact is taken as a standard for the sound intensity of 1000Hz, the frequency characteristics of loudness will be as shown in Figure 1. If we look at this qualitatively, it means that the lower the intensity of the sound, the lower the intelligibility especially in the bass part, according to the human auditory sense.

In consideration of these points, audio equipment performs a type of hearing correction so that even when the volume is turned down, the same level of intelligibility can be obtained at an appropriate volume level. FIG. 2 shows an example of such a conventional loudness control circuit. Below, FIG. 2 will be briefly explained to clarify the problems to be solved by the present invention.

The circuit shown in FIG. 2 operates as a loudness control circuit when the loudness switch S is in the solid line position shown in the drawing, and operates as a simple resistive voltage divider circuit when it is in the dotted line position. The hearing correction curve usually exhibits a frequency characteristic as shown in FIG. 3A, although it depends on the constant settings of each element (capacitors C ₁ and C ₂ and resistors R ₁ R ₂ and R ₃ ). The same is the characteristic at the switch-off position. As can be seen from this characteristic diagram, in the conventional example shown in FIG. 2, the loudness control characteristic is fixed and is unrelated to the level of the audio input signal. Taking these points into consideration, the resistance shown in Figure 2
Although it is possible to replace R ₁ and R ₂ with a volume VR as shown surrounded by a dashed-dotted line frame, if the volume becomes small and the movable terminal of the sliding volume becomes lower than the fixed central terminal 0, the frequency We cannot deny the drawback that the characteristics become constant. In addition, even if the volume is at an appropriate level and loudness control is not required, the loudness control will be activated when the loudness switch is turned on, so the frequency characteristics of the output signal will vary greatly depending on whether the loudness switch is turned on or off. You end up doing it.

In view of these points, the present invention provides a loudness control circuit that changes the frequency characteristics of the audio input signal depending on the volume in the low volume range, and can always perform optimal auditory correction for the volume of the audio input signal. It is something to do.

The details of the present invention will now be explained with reference to the drawings showing different embodiments, particularly FIGS. 4 to 8.

In the implementation circuit diagrams of Figures 4 and 5, the IC
indicates the audio signal processing IC used (for example, TA-7630P manufactured by Tokyo Shibaura Electric Co., Ltd.). This IC is equipped with independent external terminals for controlling the volume, bass, and treble characteristics, and controls the volume, bass, and treble characteristics of the audio input signals input to the input terminals individually using a DC control voltage. I'm starting to get it. Incidentally, FIG. 6 shows the bass control characteristics, and FIG. 7 shows the treble control characteristics.

Volume in audio circuits using this type of IC,
Sound quality adjustment is performed by variable voltage dividing circuits VR ₁ , VR ₂ and VR ₃ which are provided independently.

Each variable voltage divider circuit is composed of a volume having a desired rotation angle and resistance characteristics, and each has a movable terminal.
Connect so that the divided voltage generated at u ₁ , u ₂ or u ₃ is applied to the corresponding IC external terminal or in a direct current manner.

The main points of the loudness control circuit of this invention are the bass characteristic DC control circuit,
That is, the variable impedance circuit is connected in parallel between the movable terminal u ₁ of the volume VR ₁ and the ground.

The variable impedance circuit has a direct current path including a resistor R ₁ , a diode D, a transistor TR, and a resistor R ₂ , and a voltage component generated at a movable terminal u ₁ of the volume adjustment volume VR ₁ with respect to the base of the transistor T. and a control circuit that supplies a proportional DC voltage.

When the loudness control switch SL is off, the base of the transistor T is connected to a resistor R ₅ ,
It is fixedly biased by a voltage divider circuit of R ₄ and R ₃ . This fixed bias level is maintained between the terminals of the variable impedance circuit including the transistor T even if the switch SL is closed when the movable terminal u ₁ of the volume VR ₁ is at the midpoint position, that is, at the optimum volume position. Select the voltage so that it is equal to the midpoint voltage of the movable terminal of the volume.

In other words, R ₃ , R ₄ and R ₅ are the respective resistances.
When the values of R ₃ , R ₄ and R ₅ are set, and the DC voltage is Vc, (R ₃ + R ₄ )/R ₃ + R ₄ + R ₅ · Vc is the midpoint of volume VR ₁ [movable terminal U ₁ is in the center] If the voltage is located at

The loudness control switch SL is closed, and the DC divided voltage output generated at the movable terminal _u1 of the volume _VR1 is transmitted to the transistor T through the resistor _R4 .
When applied to the base of the transistor T, the collector-emitter path impedance of the transistor T changes in proportion to the divided voltage of the volume, and therefore the volume of the audio signal, and accordingly the DC control voltage to be applied to the bass control terminal changes. control.

That is, when the volume decreases, the internal (collector-emitter path) impedance of the transistor decreases proportionally, reducing the amount of current diverted to the movable terminal _u1 of the volume _VR1 . As a result, the frequency characteristics of the volume in the bass range become as shown in FIG. 8A, and the audibility is improved.

Next, when the volume increases, the frequency characteristics of the volume become as shown in FIG. 8 by performing the opposite operation, and the hearing sensitivity is corrected accordingly.

Note that the diode D connected in series to the collector of the transistor T functions as a backflow prevention device.
The resistor _R1 provided for protection is an emitter resistor.
Together with R ₂ , it limits the range of sound quality change.

The embodiment shown in FIG. 5 differs from the embodiment shown in FIG. 4 in that the transistor T' constituting the variable impedance circuit is of a PNP type. However, the variable _impedance circuit
The basic operation is almost the same as that of the embodiment shown in FIG. 4 except that it is configured to control the amount of current flowing into u′ ₁ , so the components corresponding to the implementation circuit of FIG. In contrast, by adding a dash to the same symbol, the explanation thereof will be omitted.

According to the present invention as described above, not only is hearing correction performed automatically according to the sound level, but loudness control is also performed taking into account the hearing characteristics, especially for audio signal inputs with low volume levels, so that the drawbacks of the conventional example are completely eliminated.

[Brief explanation of drawings]

1 to 3 relate to a conventional example, in which FIG. 1 is a loudness frequency characteristic diagram, FIG. 2 is a loudness control circuit diagram, and FIG. 3 is a frequency characteristic diagram of the circuit shown in FIG. 2. 4 and 8 relate to the loudness control circuit of the present invention, FIGS. 4 and 5 are circuit diagrams of different embodiments, and FIGS. 6 and 7 show the frequency characteristics of the IC used, respectively. 8th
The figure is a frequency characteristic diagram of the loudness control circuit of the present invention. IC...IC,...Volume control terminal,...Bass (bass) control terminal,...Treble (treble)...
Control terminals, VR ₁ , VR ₂ , VR ₃ ...Volume, Z...
...variable impedance circuit.

Claims (1)

[Scope of utility model registration request] A variable voltage divider circuit for volume adjustment and a variable voltage divider circuit for sound quality adjustment are respectively connected to the terminals of an audio signal processing IC that includes a volume control terminal and a sound quality control terminal such as bass and treble, and the sound quality control terminal A variable impedance circuit is connected to the variable impedance circuit, the variable impedance circuit and the variable voltage divider circuit for volume adjustment are connected via a loudness switch, and the internal impedance of the variable impedance circuit is connected to the voltage divider of the variable voltage divider circuit for volume adjustment. Loudness control circuit configured to be controlled by output.