Electronic Attenuator Apparatus

This invention relates to an electronic attenuator apparatus and more particularly to an apparatus for setting a plurality of levels in an audio instrument, for example, a volume level, a tone level and a balance level therein.

An electronic level setting apparatus (an electronic attenuator) used in a conventional audio instrument needs rather a long time to change from a given set level to other desired level. The time is represented as follows: ##EQU1##

Therefore, the apparatus has a disadvantage in that the larger the difference between the level prior to setting and the level after setting is, the longer the required time will be. Moreover, where it is required to set a plurality of levels, each of the plural level settings requires the respective level setting device and a required time for completing the change of levels increases greatly.

Therefore, an object of this invention is to provide an electronic attenuator apparatus capable of instantaneously changing a plurality of setting levels to desired ones in an audio instrument and the like.

Further, another object of this invention is to attain simplification of an electronic attenuator apparatus by reducing the number of required level setting devices to one.

In order to attain the above objects, according to this invention, the attenuation factor of a voltage controlled attenuator is controlled by the level of a voltage supplied from a memory circuit selectively set. Moreover, in this invention, a plurality of switches may be used, as level setting means, to provide a level signal.

FIG. 1 is a block diagram of a preferred form of an electronic attenuator according to this invention.

FIG. 2 is a block diagram of one level setting portion of another form of an electronic attenuator according to this invention.

FIG. 3 is a block diagram of still another form of an electronic attenuator according to this invention.

FIG. 4 is a circuit diagram showing a modification of voltage sources illustrated in FIGS. 2 and 3.

In FIG. 1, a voltage controlled attenuator VCA (VCA.sub.1 -VCA.sub.3) operates to determine an attenuation factor between an input IN (IN.sub.1 -IN.sub.3) and an output OUT (OUT.sub.1 -OUT.sub.3) in response to the level of an analog signal (voltage) from a D - A converter DAC (DAC.sub.1 -DAC.sub.3). The D - A converter DAC converts a digital signal temporarily stored in a memory circuit (latch circuit) LA (LA.sub.1 -LA.sub.3) into the analog signal. A decimal to binary converter circuit DBC converts a decimal level signal set by switches SW.sub.1 -SW.sub.n, connected in parallel thereto, to a binary level signal and provides it to the memory circuit LA. The switches are weighted in accordance with the decimal system.

A memory circuit LA.sub.1 stores the binary level signal from the decimal-binary converter circuit DBC when the output signal of a NOR gate G is high. A memory circuit LA.sub.2 stores the binary level signal when the output signal of a tone timer TMT is high and a memory circuit LA.sub.3 stores it when the output signal of a balance timer TMB is high. The tone timer TMT and the balance timer TMB are triggered by make signals of manual switches SWT and SWB, respectively, and then provide output signals to the memory circuits LA.sub.2 and LA.sub.3 and to the NOR gate G for a given time irrespective of the make times of said switches. Further, the timer TMT provides its output signal to the timer TMB and vice versa so that an output signal of one of them may be inhibited from being supplied to the memory circuit while the other operates, and switches of non-lock type may be preferred as the switches SW.sub.1 -SW.sub.n, SWT and SWB.

Now, an audio signal is applied to the input IN.sub.1 of the voltage controlled attenuator VCA.sub.1 and is attenuated in accordance with an attenuation factor set therefor to provide an attenuated audio signal at an output OUT.sub.1 thereof. Its volume level is indicated by a digital indicator IND.sub.1 based on the binary level signal stored in the memory circuit LA.sub.1. Illuminated-type switches (not shown) may alternatively be coupled with the switches SW.sub.1 -SW.sub.n instead of the digital indicator.

When any one of the switches SW.sub.1 -SW.sub.n is selected and depressed to obtain a desired volume level, the decimal-binary converter circuit DBC converts a decimal level signal set by the selected switch to a binary level signal and provide it to the input of the memory circuits. At that time, the output signals of the tone timer TMT and the balance timer TMB are at low levels and, therefore, the output signal of the NOR gate G is at a high level, so that only the memory circuit LA.sub.1 stores the binary level signal. This signal stored in the memory circuit LA.sub.1 is converted to an analog signal (voltage) by the D-A converter DAC.sub.1. The voltage controlled attenuator VCA.sub.1 attenuates an audio signal applied to the input IN.sub.1 thereof in accordance with the output of the D-A converter DAC.sub.1 to provide an attenuated audio signal to the output OUT.sub.1 thereof. The aforesaid attenuating level change of volume in the voltage controlled attenuator VCA.sub.1 can be done instantaneously.

Where it is intended to set a desired tone level, the tone switch SWT is depressed. In this case, the switches SW.sub.1 -SW.sub.n are representative of the respective tone levels. The tone timer TMT holds the output signal thereof at a high level during a time which is usually required from depression of the tone switch SWT to depression of any one of the switches SW.sub.1 -SW.sub.n, and inhibits the output signal of the balance timer TMB from being produced. Said time is freely adjustable. The decimal level signal provided by the switches SW.sub.1 -SW.sub.n is stored only in the memory circuit LA.sub.2 while the output signal of the tone timer TMT is high. A tone setting signal applied to the input IN.sub.2 of the voltage controlled attenuator VCA.sub.2 may be controlled in a similar manner to that in the volume level setting as previously described. When the tone timer TMT output changes to low after the preset time has passed, the output of the converter DBC returns to such condition that it may be stored in the memory. Balance level setting may be done in a similar manner to the tone level setting.

FIG. 2 is a circuit diagram of another embodiment of this invention, showing only one level setting portion thereof. In this embodiment, by selection of one of the switches SW.sub.1 -SW.sub.n, a voltage is selected from voltage sources V.sub.1 -V.sub.m and is supplied to a voltage controlled attenuator VCA.

FIG. 3 shows still another embodiment of this invention. In the circuit as illustrated in the figure, in order to selectively set a plurality of levels, for example three levels, memory circuits (latch circuits) LA.sub.1 -LA.sub.3 and a selector circuit comprising a NOR gate G and two timers TMT and TMB analogous to like elements shown in FIG. 1, are disposed between a level setting circuit comprising switches SW.sub.1 -SW.sub.n and voltage sources V.sub.1 -V.sub.m, and voltage controlled attenuators VCA.sub.1 -VCA.sub.3.

The operation of the above embodiment will be easily understood by referring to the operation of the foregoing embodiments illustrated in FIGS. 1 and 2. Further, as shown in FIG. 4 the voltage sources may be replaced with a plurality of resistors R.sub.1 -R.sub.i connected in series across one voltage source V.sub.o.

As described above, according to this invention, a defect involved in a conventional electronic attenuator, in that it takes a considerable time to obtain a desired level setting condition, can be eliminated. Furthermore, even when plural level setting is required, the attenuating apparatus of this invention needs not more than one level setting circuit and a selector circuit, simplifying the construction of the apparatus. In addition, the time required for level setting is much reduced.