JP2000222826A - Mute apparatus at d/a conversion apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a good S/N ratio at the time of D/A conversion to non- compressed and compressed signals by sending a mute signal when the non- compressed signal becomes a signal indicating silence, not sending the mute signal when an extension signal becomes the signal indicating silence and sending an auxiliary mute signal when an analog sound signal which is a D/A converted extension signal becomes the signal indicating silence. SOLUTION: A data-processing part 4 sends a digital sound signal obtained by extending a compressed signal when a restored digital sound signal is the compressed signal, or a non-compressed signal when the restored signal is the non-compressed signal to a D/A converter 5 and a mute judge part 6. Moreover, the data-processing part sends to an auxiliary mute judge part 8 an output 34 indicating whether it is the compressed signal or non-compressed signal. The mute judge part 6 sends out a mute signal to an output 32 only when the non-compressed signal is sent and the signal is a signal indicating silence. The auxiliary mute judge part 8 outputs an auxiliary mute signal when an analog sound signal is soundless at the time of reproducing the compressed signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a D / A converter for converting a compressed digital audio signal and an uncompressed digital audio signal into an analog audio signal, and more particularly, to a D / A converter. The present invention relates to a mute device for setting a signal amplifying circuit for amplifying an analog audio signal to a mute state when silence occurs during reproduction of both uncompressed digital audio signals.

[0002]

2. Description of the Related Art A DVD, which is a recording medium that has begun to be widely used, records a digital audio signal (hereinafter, referred to as an uncompressed signal) of a linear PCM which enables high-quality recording, and compresses the signal. It is possible to record a digital audio signal (hereinafter, referred to as a compressed signal). For this reason,
An apparatus for reproducing a DVD has a function of converting an uncompressed signal into an analog audio signal and a function of converting a compressed signal into an analog audio signal. Also, S /
In order to set the N ratio to a good value, a mute determination unit that generates a mute signal when the uncompressed signal indicates silence is provided, and when a mute signal is generated, a signal amplification circuit that amplifies an analog audio signal is provided. It is set to a mute state (referred to as a first related art).

[0003] Further, in the prior art for muting,
There is a technique proposed as JP-A-57-55511. In other words, with this technology, like between music pieces,
When the audio signal becomes silent, a recognition signal is recorded on a magnetic tape. When reproducing, when a recognition signal is detected, the mute circuit is turned on to prevent the hissing noise of the magnetic tape from being output (this is referred to as a second related art).

[0004]

However, when the above technique is used, the following problems have occurred. That is, the mute determination unit in the first related art is configured to operate only at the time of reproducing an uncompressed signal requiring particularly high sound quality. That is, the mute determination unit generates a mute signal when the uncompressed signal indicates silence, but does not generate a mute signal when the decompressed signal obtained by expanding the compressed signal becomes silence. Therefore, when a DVD on which a compressed signal is recorded is reproduced, the signal amplifier circuit is not set to the mute state even when there is no sound. Therefore, even when there is no sound, the noise component generated in the path of the signal amplification circuit (such as an OP amplifier) is transmitted from the signal amplification circuit. As a result, the DV in which the compressed signal is recorded
When reproducing D, a DVD on which an uncompressed signal is recorded
In this case, the S / N ratio is greatly deteriorated as compared with the case of reproducing.

The second prior art is a technique applied to a recording medium capable of recording a recognition signal when a sound signal to be recorded is silent. Therefore, it has been difficult to apply the present invention to an apparatus for reproducing a DVD in which a recognition signal is not allowed to be recorded in a silent portion.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an analog audio signal obtained by D / A conversion when reproducing a compressed signal. When the signal indicates silence, the signal amplifying circuit for amplifying the analog audio signal is set to a mute state, so that the S / N signal is obtained both when the D / A conversion of the uncompressed signal and the D / A conversion of the compressed signal are performed. It is an object of the present invention to provide a mute device in a D / A converter that can improve a ratio.

Another object of the present invention is to provide a D / A converter capable of improving the S / N ratio when reproducing a DVD on which a compressed signal is recorded. An object of the present invention is to provide a mute device.

[0008]

According to a first aspect of the present invention, there is provided a mute device for a digital-to-analog (D / A) conversion apparatus, wherein when a compressed signal, which is a compressed digital audio signal, is guided, An analog audio signal is generated by performing D / A conversion of an expanded signal obtained by expanding the compressed signal. When an uncompressed signal that is an uncompressed digital audio signal is derived, the uncompressed signal is converted to a digital signal. The present invention is applied to a D / A converter that generates an analog audio signal by performing a / A conversion. When the uncompressed signal becomes a signal indicating silence, a mute signal is transmitted. When the decompressed signal becomes a signal indicating silence, A mute determining unit that does not transmit a mute signal;
An auxiliary mute determination unit for transmitting an auxiliary mute signal when the A-converted analog audio signal becomes a signal indicating silence; and a signal amplifier for amplifying the analog audio signal when the mute signal or the auxiliary mute signal is transmitted. And a mute setting unit for setting the circuit to a mute state.

That is, when the uncompressed signal becomes a signal indicating silence, a mute signal is transmitted, and the signal amplifier circuit is set to a mute state. When the expanded signal is a signal indicating silence, the analog audio signal is also a signal indicating silence. Therefore, when the decompression signal becomes a signal indicating silence, the auxiliary mute signal is transmitted, and the signal amplifier circuit is set to the mute state.

[0010] In the D / A converter according to the second aspect of the present invention, in addition to the above configuration, the compressed signal is a signal obtained by reproducing a DVD.

That is, when reproducing a DVD on which a compressed signal is recorded, when the compressed signal becomes a signal indicating silence, the signal amplifier circuit is set to a mute state.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below.
This will be described with reference to the drawings. FIG. 1 shows the D / according to the present invention.
FIG. 2 is a block diagram illustrating an electric configuration of an embodiment of a mute device in the A-converter.
And a D / A converter 1 for converting a digital audio signal read by the pickup 3 into an analog audio signal.

In FIG. 1, a disk 2 is a compressed digital audio signal (hereinafter referred to as a compressed signal) such as an AC-3 signal or an uncompressed digital audio signal such as a linear PCM signal. Signal (below,
The DVD is recorded with an uncompressed signal. The pickup 3 is a block for reading a digital audio signal recorded on the DVD 2, and sends the read digital audio signal to the data processing unit 4.

The data processing section 4 is a block for restoring the recorded digital audio signal by decoding and error correcting the digital audio signal sent from the pickup 3. If the restored digital audio signal is a compressed signal, the digital audio signal obtained by expanding the compressed signal (hereinafter referred to as an expanded signal) is determined by the D / A converter 5 to be muted. And sends it to the section 6. When the restored digital audio signal is an uncompressed signal, the restored uncompressed signal is
The signal is sent to the A converter 5 and the mute judging unit 6. Further, an output 34 indicating whether the signal from the pickup 3 is a compressed signal or an uncompressed signal is sent to the auxiliary mute determination unit 8.

The D / A converter 5 performs D / A conversion of a digital audio signal (decompressed signal and uncompressed signal) sent from the data processing section 4 to convert an analog audio signal 31L for the left channel into a right analog signal 31L. This is a block for generating a channel analog audio signal 31R. Then, the generated analog audio signals 31L and 31R are sent to the signal amplifier circuits 9L and 9R.

The mute judging section 6 sends a mute signal (L level) to an output 32 when the signal sent from the data processing section 4 is an uncompressed signal and when the uncompressed signal becomes a signal indicating silence. It is a block. When the signal transmitted from the data processing unit 4 is a compressed signal, the mute signal is not transmitted even when the compressed signal is a signal indicating silence. That is, the mute determination unit 6
Is an uncompressed signal sent from the data processing unit 4, and
The mute signal is transmitted only when the uncompressed signal becomes a signal indicating silence.

The auxiliary mute judging section 8 outputs the expanded signal to D /
When the A-converted analog audio signal becomes a signal indicating silence, the block outputs an auxiliary mute signal (L level) to the output 33. That is, when the output 34 from the data processing unit 4 indicates that the compressed signal is reproduced, when the levels of the analog audio signals 31L and 31R transmitted from the D / A converter 5 become levels indicating silence, The output 33 is set to L level.

The signal amplification circuit 9L amplifies the left channel analog audio signal 31L sent from the D / A converter 5, and sends the amplified audio signal to the output terminal 10L as a line level signal. It has become.
That is, the analog audio signal 31L is guided to the amplifier circuit 11 having low-pass characteristics via the coupling capacitor C1 and amplified. The amplified signal is output to the output terminal 1 via the capacitor C2 and the resistor 1.
It is led to 0L. The signal amplification circuit 9R has the same configuration as the signal amplification circuit 9L. That is, D / A
The analog audio signal 31R for the right channel transmitted from the converter 5 is amplified, and the amplified audio signal is transmitted to the output terminal 10R as a line-level signal.

The mute setting section 7 outputs a mute signal from the mute judging section 6 (when the output 32 goes low) or an auxiliary mute signal from the auxiliary mute judging section 8 (output). 33 is at L level), by connecting each of the output terminals 10L and 10R to the ground level, the signal amplifying circuits 9L and 9R are connected.
9R is a block for setting the mute state.

FIG. 2 is a block diagram showing a detailed electrical configuration of the auxiliary mute judging section 8. As shown in FIG.

The analog audio signal 31L is guided to a minus input of the OP amplifier 21 via a coupling capacitor C3 and a resistor R2. The analog audio signal 31R is guided to the minus input of the OP amplifier 21 via the coupling capacitor C4 and the resistor R3. A resistor R4 is connected between the negative input and the output of the OP amplifier 21, and a capacitor C5 for obtaining low-pass characteristics is connected. A reference voltage r for setting the operating point of the OP amplifier 21 is applied to a connection point between the capacitor C3 and the resistor R2 via a resistor R6. Also, the capacitor C4 and the resistor R
A reference voltage r is applied to a connection point with the reference 3 through a resistor R7. Further, a reference voltage r is applied to the plus input of the OP amplifier 21 via a resistor R5.

The connection between the analog audio signals 31L and 31R and the OP amplifier 21 has the above-described relationship. For this reason, the OP amplifier 21 performs addition and amplification of the analog audio signal 31L and the analog audio signal 31R. Then, the amplified signal is sent to the A / D converter 22. Note that the amplification factor of the OP amplifier 21 is the analog audio signal 31
In order to increase the detection sensitivity of whether or not L and 31R are silent, for example, a high amplification factor such as 1000 times is set.

The A / D converter 22 is a block for converting an analog signal transmitted from the OP amplifier 21 into a digital value and transmitting the digital value to the determination unit 23. Also, the judgment unit 2
3 indicates that when the output 34 indicates the reproduction of a compressed signal, A /
By determining the level of the D converter 22, it is a block for determining whether or not the analog audio signals 31L and 31R are silent. When it is determined that the analog audio signals 31L and 31R are silent, an auxiliary mute signal (L level) is sent to the output 33.

The A / D converter 22 and the determination unit 23 are constituted by a microcomputer provided for controlling the main operation of the device.

FIG. 3 is a circuit diagram showing a detailed electrical connection of the mute setting section 7. As shown in FIG. The output 32 from which the mute signal is sent is connected to the cathode of the diode D3, and the output 33 from which the auxiliary mute signal is sent is the diode D4.
Connected to the cathode. And the diode D3
And the anode of the diode D4 are connected to each other, and the transistor Q2 is connected via a resistor R8.
Led by the base. The emitter of the transistor Q2 is connected to a positive power supply.

The collector of the transistor Q2 is led to the base of the transistor Q3 via the resistor R9, and the emitter of the transistor Q3 is grounded.
The collector of the transistor Q3 is guided to the signal amplification circuit 9L as an output 35L for setting the signal amplification circuit 9L to a mute state. Also, the transistor Q3
Of the transistor Q3 between the collector of
The resistor R10 and the capacitor C7 are connected in order to prevent the occurrence of switching noise due to the change of ON / OFF of the switch. The block 25R for setting the signal amplifying circuit 9R to the mute state is a block 2 including resistors R9 and R10, a capacitor C7, and a transistor Q3.
It has the same configuration as 5L.

The mute setting section 7 has the above-described configuration. Therefore, when the mute signal is sent from the mute judging section 6 (when the output 32 goes low) or when the auxiliary mute signal is sent from the auxiliary mute judging section 8 (when the output 33 goes low). ), The transistor Q2 is turned on and the transistor Q3 is turned on. Therefore, both the outputs 35L and 35R are connected to the ground level, and the signal amplifying circuit 9
L and 9R are set to the mute state.

The operation of the embodiment having the above configuration will be described. Now, since the reproduction of the DVD 2 is not performed, the mute judging section 6 is in a state of transmitting a mute signal (the output 32 is set to L level), and the auxiliary mute judging section 8
Is in a state in which an auxiliary mute signal is transmitted (output 33 is set to L level). In this state, when the reproduction of the DVD 2 on which the compressed signal is recorded is started, the data processing unit 4 sends the expanded signal obtained by expanding the compressed signal to the D / A converter 5 and the mute judging unit 6. Send out. Further, the data processing unit 4 notifies the auxiliary mute determination unit 8 that the compressed signal is to be reproduced.

The output level of the OP amplifier 21 provided in the auxiliary mute judging section 8 is determined by the analog audio signals 31L and 3L.
When 1R is a signal indicating silence, that is, when the expanded signal is a signal indicating silence, the level is equal to the reference voltage r. Also, the analog audio signals 31L, 31R
Is a signal indicating a sound, that is, when the decompressed signal is a signal indicating a sound, the level is out of the reference voltage r.

Therefore, when a signal indicating sound appears in the analog sound signals 31L and 31R obtained by D / A converting the expanded signal, the output level of the OP amplifier 21 becomes a level deviating from the reference voltage r. The determining unit 23 that has detected that the output level of the OP amplifier 21 has deviated from the reference voltage r determines that the output of the sound by the reproduction of the expanded signal has started, and immediately changes the output 33 from the L level to the H level. . On the other hand, when the decompression signal is transmitted from the data processing unit 4, the mute determination unit 6 stops transmitting the mute signal (changes the output 32 to the H level). As a result, the transistor Q2 turns off and the transistor Q3 turns off.
Therefore, the signal amplifier circuits 9L and 9R are set in a state where the mute is released.

When the expanded signal changes from the above state to a signal indicating silence, the output value of the A / D converter 22 shows a value equal to the reference voltage r. The determining unit 23, which has detected that the output value of the A / D converter 22 has become equal to the reference voltage r, sets this state (a state in which the output value of the A / D converter 22 is equal to the reference voltage r) for a certain period of time. (E.g., one second), it is determined whether or not to continue. Then, the state (A /
When the output value of the D converter 22 is equal to the reference voltage r) for a certain period of time, it is determined that the decompressed signal is silent, and the output 33 has an L level (auxiliary mute signal).
Is sent. As a result, the transistor Q2 changes from the off state to the on state, and the transistor Q3 turns on. Therefore, the signal amplification circuits 9L and 9R are set to a mute state.

On the other hand, when the state in which the output value of the A / D converter 22 indicates the reference voltage r is a temporary one and does not continue for a certain period of time, the determination unit 23 sets the instantaneous silent period. It is determined that there is, and the output is not changed from the H level.
Therefore, the signal amplifying circuits 9L and 9R are maintained in the mute release state.

The operation at the time of reproducing a compressed signal has been described above, and then the operation at the time of reproducing an uncompressed signal will be described. D
When the reproduction of the DVD 2 on which the non-compressed signal is recorded is started in a state where the reproduction of the VD 2 is not performed, the data processing unit 4 sends the non-compressed signal to the D / A converter 5 and the mute determination unit 6. . Further, the data processing unit 4 notifies the auxiliary mute determination unit 8 that the reproduction of the uncompressed signal is performed. The determination unit 23 notified of the reproduction of the uncompressed signal keeps the output 33 at the H level and does not transmit the auxiliary mute signal until the reproduction of the uncompressed signal ends.

On the other hand, the mute judging section 6 sends a mute signal (L level) to the output 32 when the uncompressed signal becomes a signal indicating silence, and outputs a mute signal when the uncompressed signal becomes a signal indicating sound. Is stopped (output 32 is set to H level). Therefore, when the uncompressed signal becomes a signal indicating silence, the signal amplifier circuits 9L and 9R are set to a mute state, and when the uncompressed signal becomes a signal indicating sound, the signal amplifier circuits 9L and 9R cancel muting. Set to state.

Note that the present invention is not limited to the above embodiment, and the D / A converter 1 has been described as having a configuration in which a signal from the pickup 3 is guided. However, as another configuration, for example, a digital The same can be applied to a configuration in which a signal from a tuner unit that receives a broadcast is guided.

In the above, a case where a line-level audio signal is output has been described. However, the present invention can be similarly applied to other configurations such as a configuration in which a power amplifier circuit and a speaker are added. Is possible.

[0037]

The mute device in the D / A conversion device according to the first aspect of the present invention provides a D / A conversion of an expanded signal obtained by expanding a compressed digital audio signal and an uncompressed uncompressed digital audio signal. The present invention is applied to a D / A converter that performs D / A conversion of a signal, and sends a mute signal when the uncompressed signal becomes a signal indicating silence, and outputs a mute signal when the decompressed signal becomes a signal indicating silence. A mute determination unit that does not transmit, and an auxiliary mute determination unit that transmits an auxiliary mute signal when the analog audio signal obtained by D / A converting the expanded signal becomes a signal indicating silence;
When the mute signal or the auxiliary mute signal is transmitted, a mute setting unit that sets a signal amplifier circuit that amplifies the analog audio signal to a mute state is provided. Therefore, when the uncompressed signal becomes a signal indicating silence, a mute signal is transmitted, and the signal amplifier circuit is set to a mute state. When the expanded signal becomes a signal indicating silence, an auxiliary mute signal is sent out, and the signal amplifier circuit is set to a mute state. Therefore, the D / A conversion of the uncompressed signal and the D / A
It is possible to improve the S / N ratio both at the time of conversion and at the time of conversion.

According to a second aspect of the present invention, in the D / A conversion device, the mute device includes:
Is a signal obtained by reproduction. For this reason, when reproducing the DVD on which the compressed signal is recorded, if the compressed signal becomes a signal indicating silence, the signal amplifying circuit is set to the mute state.
Is reproduced, it is possible to improve the S / N ratio.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an electrical configuration of an embodiment of a mute device in a D / A converter according to the present invention.

FIG. 2 is a block diagram showing a detailed electrical configuration of an auxiliary mute determination unit.

FIG. 3 is a circuit diagram showing detailed electrical connection of a mute setting unit.

[Explanation of symbols]

 Reference Signs List 1 D / A converter 2 DVD 4 Data processing unit 6 Mute determination unit 7 Mute setting unit 8 Auxiliary mute determination unit 9L, 9R Signal amplification circuit 32 Mute signal 33 Auxiliary mute signal 34 Output indicating that it is a compressed signal

Claims (2)

[Claims] When a compressed signal, which is a compressed digital audio signal, is derived, an analog audio signal is generated by performing D / A conversion of an expanded signal obtained by expanding the compressed signal. When a non-compressed signal that is a digital audio signal that is not compressed is introduced, a D / A converter that generates an analog audio signal by performing D / A conversion on the uncompressed signal, wherein the uncompressed signal indicates silence A mute determination unit that sends out a mute signal when the expansion signal becomes a signal indicating silence, and a mute determination unit that does not send a mute signal when the expansion signal becomes a signal indicating silence, and the analog audio signal obtained by D / A converting the expansion signal becomes a signal indicating silence. Sometimes an auxiliary mute determination unit that sends an auxiliary mute signal, and when the mute signal or the auxiliary mute signal is sent A mute setting unit for setting a signal amplification circuit for amplifying the analog audio signal to a mute state. 2. The mute device according to claim 1, wherein the compressed signal is a signal obtained by reproducing a DVD.