JPH012413A - Fade-in/fade-out circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fade-in/fade-out circuit suitable for an audio signal system having a signal level adjustment circuit.

[Conventional technology]

Conventionally, when performing standard audio recording in a video tape recorder (VTR), for example, in order to fade in and fade out the audio in accordance with the image, as shown in Fig. 4, an audio signal processing IC 2 and an electronic A combination with a volume IC 4 is being carried out. That is,
The input signal ■i applied to the input terminal 6 from a signal source such as a microphone is faded in and faded out using the electronic volume IC 4 to adjust the level as desired, and then sent from the terminal 8 to the audio signal processing IC 2. and predetermined processing is performed. Then, the output signal ■ obtained by the audio signal processing IC 2.

is recorded from the output terminal 10 onto a magnetic tape as a recording medium.

[Problem that the invention seeks to solve]

If the fade-in/fade-out circuit is configured by placing the electronic volume IC 4 in the front stage in this way, signal processing will become complicated, leading to a deterioration of the S/N ratio, and it will be necessary to install the electronic volume IC 4 separately. There are disadvantages such as increased equipment cost.

Therefore, the present invention aims at reducing the area of the circuit by using the existing level adjustment circuit, and at the same time, prevents the deterioration of the S/N ratio.

[Means for solving problems]

The fade-in/fade-out circuit of the present invention has a first
As shown in the figure, an arbitrary external control is applied to the output side of a filter 34 that applies a level control signal according to the output signal to the level adjustment means (volume circuit 22) for the input signal level. A control input means (variable voltage source 42) that provides 111 input is installed, and fade-in/fade-out is performed by adjusting the control input.

[Function] With this configuration, it is possible to use the control input means (variable voltage source 42) from the output side of the filter 34 that provides a level control signal to the existing level adjustment means (volume circuit 22). Fade-in and fade-out can be performed by applying arbitrary control inputs, and fade-in and fade-out can be realized using, for example, an existing audio signal processing IC without adding an electronic volume IC.

〔Example〕

FIG. 1 shows an embodiment of the fade-in/fade-out circuit of the present invention.

This fade-in/fade-out circuit is an A L
C (Automatic Level Control)
l) It is composed of a system of volume circuits and mute circuits that form a circuit.

An input signal vi, such as a voice for recording, is applied to the input terminal 12 from a signal source such as a microphone, and this input signal V is applied to the amplifier 16 through a resistor 14. The input side of this amplifier 16 has a mute input terminal 1.
A mute switch 20 which is opened and closed by a mute signal (1) applied to the circuit 8 is installed to add a mute circuit, and a volume circuit 22 is installed as a level adjustment means.

Output signal of amplifier 16■. is taken out as a recording output from the output terminal 24, and A for level detection.
This ALC detection circuit 26 is added to the LC detection circuit 26.
The detected output is converted to a DC level by a filter 34, for example, made up of a resistor 30 and a capacitor 32, which is connected to a filter terminal 2B formed as an external terminal of the IC. This DC level is applied as a control input to the base of transistor 36, through which the impedance of volume circuit 22 is controlled.

The volume circuit 22 includes a transistor 224 that flows an operating current through a differential pair of transistors 220 and 222, and transistors 226 and 228 that form a current mirror circuit as a load, and connects the base of the transistor 220 to the input and output terminals. part, transistor 222
A reference voltage (2) is set to the 0 base by the voltage a230.

In the audio signal system circuit including the volume circuit 22 and the mute circuit as described above, the switch 40 is connected to the control input side of the volume circuit 22, that is, the filter terminal 28.
A variable voltage T is used as a control input means to provide a control input for performing fade-in/fade-out from the outside via
Connect A42.

With this configuration, when the switch 40 is open, a normal ALC circuit is configured, the impedance of the volume circuit 22 is controlled according to the input level, and an output signal v0 of a constant level is taken out from the output terminal 24.

Then, the switch 40 is closed, and the control voltage 2 is applied by the variable voltage source 42 as shown at A in FIG. When gradually increasing the volume circuit 2 through the transistor 36,
2 increases, its input impedance decreases and the degree of level suppression increases, resulting in a fade-out condition as shown in FIG. 2C. At the lower limit of this fade-out state, as shown in B in Figure 2,
When the mute signal V changes from the low (L) level to the high (H) level and the mute switch 20 is closed, the input signal V to the amplifier 16 is released and no signal is output.

Furthermore, when the control voltage VC provided by the variable voltage source 42 is gradually lowered with the switch 40 closed, the operating current flowing to the volume circuit 22 through the transistor 36 is reduced, so its input impedance increases.
The degree of level suppression is reduced, resulting in a fade-in state. Therefore, by adjusting the control voltage (1) of the variable voltage source 42, fade-in and fade-out can be obtained.

In the embodiment shown in FIG. 1, the variable voltage a@42 is connected to the filter terminal 28 as a control input means, but as shown in FIG. By installing a current mirror circuit 48 as a control input means for fade-in/fade-out, and adjusting the control current 1c applied from the terminal 50 to the base and collector of the transistor 46, which are shared with the base of the transistor 44, , the impedance of the volume circuit 22 can be forcibly increased or decreased from the outside, and fade-in/fade-out can be similarly achieved.

〔Effect of the invention〕

According to this invention, it is possible to perform level control by applying an arbitrary control input using the control input means from the output side of the filter that applies a level control signal to the existing level adjustment means. Without adding a volume IC, the circuit can be simplified by using the existing level adjustment circuit, and fade-in/fade-out can be realized while preventing deterioration of the S/N ratio.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the fade-in/fade-out circuit of the present invention, FIG. 2 is a diagram showing the operation of the fade-in/fade-out circuit shown in FIG. 1, and FIG. 3 is a circuit diagram showing an embodiment of the fade-in/fade-out circuit of the present invention.・Circuit diagram showing another embodiment of the fade-out circuit. FIG. 4 is a diagram showing a conventional fade-in/fade-out circuit. 22...Volume circuit 34...Filter 42...Variable voltage source (control input means) 48...Current mirror circuit Fig. 3 Fig. 4

Claims (1)

[Claims] Control input means for applying an arbitrary control input from the outside is installed on the output side of the filter that applies a level signal according to the output signal to the level adjustment means for the input signal level, and fade-in and Fade-in/fade-out circuit that performs fade-out.