JP2003009297A - Signal processing circuit and signal processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a signal processing circuit that can reproduce a proper audio signal even when a decode system is switched. SOLUTION: When 'SW' exists, a control section connects a switch SW11 to a position 2. When 'L' and 'R' are small, switches SW1, SW3 are closed and switches SW6, SW8 are thrown to the position 2. When no 'C' exists, a switch SW13 is closed and when 'C' exists and is small, a switch SW2 is closed and a switch SW7 is thrown to the position 2. When no 'Sl', 'Sr' exist, the SW13, SW14, SW15 or SW16, SW17 are closed. When 'Sl', 'Sr' exist and are small, switches SW4, SW5 are closed and switches SW9, SW10 are thrown to the position 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing circuit and a signal processing method.

[0002]

2. Description of the Related Art In recent years, due to advances in audio compression technology and signal processing technology, in place of conventional two-channel audio signals,
AV (audio / visual) devices capable of reproducing multi-channel audio signals having three or more channels have become widespread. For example, DVD (Digi
Digital audio encoded by a predetermined method is recorded on an optical disc such as a tal versataile disk), and a DVD player decodes this digital audio recorded on a DVD by a corresponding decoder to perform multi-channel decoding. Play the audio signal of. Specifically D
The VD player is, for example, an A developed by Dolby Laboratories.
C3 method (Dolby Digital), DT
DTS method (Digital Theater System;
Digital Theater System), MPEG (Motion Pic)
tureExperts Group) Multi-channel system and D
A decoder such as a VD audio multi-channel system (PCM multi-channel) is provided. Of these, AC3
Regarding the system type decoder, refer to "Dolby Licensee Information Manual: Dolby Digital Consumer Decoder" of Dolby Laboratories, which corresponds to the number of loudspeakers connected to a DVD player etc. and the low frequency reproduction capability. Techniques for appropriately adding signals and appropriately changing low-frequency components are standardized.

A signal processing circuit incorporated in a DVD player or the like will be described below with reference to FIG. 6 and the like.
FIG. 6A is a block diagram showing an example of an AC3 decoder 91 and a sub-management 92 which form a signal processing circuit, and FIG. 6B shows one of other decoders which form a signal processing circuit. 3 is a block diagram showing a DTS decoder 93 which is The signal processing circuit may additionally include a decoder compatible with the MPEG multi-channel system and the DVD audio multi-channel system.

The AC3 decoder 91 is a decoder for decoding a digital signal of the AC3 system, and also the DTS.
The decoder 93 is a decoder that decodes a DTS system digital signal. That is, the signal processing circuit is
When a digital signal encoded by the AC3 system is input by streaming by reproducing D, the AC3 decoder 9
1 and the sub management 92 are used to generate a multi-channel audio signal. When an audio streaming encoded by the DTS method is input, the DTS decoder 93 is used to generate a multi-channel audio signal. Specifically, the AC3 decoder 91 decodes a digital signal encoded by the AC3 system to obtain Lch, Cch, Rch, Slc.
6 channels of h, Srch, and LFEch (5.1
Channel) audio signal. The AC3 decoder 91 supplies the generated audio signal of each channel to the sub management 92.

As shown in FIG. 7, the sub-management 92 includes high-pass filters F1 to F5, low-pass filter F6, attenuators A1 to A6, an amplifier A7, and
It is composed of switches SW1 to SW11 and adders AD1 to AD3. The high-pass filters F1 to F5 are, for example, 100 Hz from the signals respectively supplied via the input side Lch, Cch, Rch, Slch and Srch.
Cut the following low-frequency components and switch SW6 to SW1
Supply to 0. The low-pass filter F6 has an adder AD1.
For example, the high-frequency component of 100 Hz or higher is cut from the signals added in step S4 and supplied to the switch SW11.

The attenuators A1 to A5 are, for example, -1.
5dB attenuator, Lch, Cc on input side
The signals supplied via h, Rch, Slch, and Srch are attenuated and supplied to the switches SW1 to SW5. Further, the attenuator A6 is, for example, an attenuator of −5 dB, attenuates the signal supplied via the LFEch on the input side, and supplies the attenuated signal to the adder AD1. The amplifier A7 is, for example, a +10.5 dB amplifier, amplifies the signal supplied via the switch SW11, and supplies the amplified signal to the adders AD2 and AD3.

The switches SW1 to SW5 turn on / off the connection between the attenuators A1 to A5 and the adder AD1. The switches SW6 to SW10 are Lc on the input side.
Any one of the signals supplied via h, Cch, Rch, Slch, and Srch and the signals passed through the high-pass filters F1 to F5 is selected and supplied to the adders AD2, AD3 and the like. Then, the switch SW11 passes the signal that has passed through the low-pass filter F6 to the amplifier A7 and the output-side S.
Supply by switching to any of Wch.

The adder AD1 includes attenuators A1 to A5.
The signal passed through (when the switches SW1 to SW5 are on) and the signal passed through the attenuator A6 are added and supplied to the low pass filter F6. Also, the adder AD2
Adds the signal supplied via SW6 and the signal passed through the amplifier A7, and supplies the result to the Lch on the output side. Then, the adder AD3 adds the signal supplied via the SW8 and the signal passed through the amplifier A7, and outputs the R on the output side.
supply to ch.

The initial setting process for switching the connection of the switches SW1 to SW11 in the sub management 92 will be described below with reference to FIG. Figure 8
In order to appropriately change the distribution of low frequency components, etc., in accordance with the number of speakers and the bass reproduction capability, the switches SW1 to S1
It is a flowchart explaining the initialization process which switches the connection of W11. The initial setting process is executed by a control unit (microcomputer or the like) (not shown), and the connection settings of the switches SW1 to SW11 that have been switched are held in the memory or the like.

First, the control unit is a subwoofer ("SW").
It is determined whether or not (step S101). That is, the control unit determines whether or not the “SW” is connected to the DVD player or the like according to the setting information or the like input via a predetermined operation unit or the like. When determining that there is "SW", the control unit connects the switch SW11 to 2 (on the SWch side) (step S102). That is, the control unit switches the switch SW11 so that the signal that has passed through the low-pass filter F6 is supplied to the SWch on the output side.

Next, the control section determines the size of the left speaker ("L") and the right speaker ("R") (step S103). That is, the control unit determines whether “L” and “R” connected to the DVD player or the like have a size capable of reproducing a frequency band of 100 Hz or less.
When the control unit determines that “L” and “R” are small (the frequency band of 100 Hz or less cannot be reproduced), the switch SW
1, SW3 is turned on, and switches SW6 and SW
8 is connected to 2 (high-pass filter side) (step S
104). On the other hand, "L" and "R" are large (100Hz
When it is determined that the following frequency bands can be reproduced), the control unit turns off the switches SW1 and SW3 and connects the switches SW6 and SW8 to 1 (Lch, Rch side) (step S105).

Subsequently, the control unit determines the presence / absence of the center speaker ("C") and the size thereof (step S10).
6). That is, the control unit determines the presence / absence of “C” and whether or not the frequency band of 100 Hz or less can be reproduced when “C” is present. When the control unit determines that there is no "C", the control unit A
The C3 decoder 91 downmixes Cch into Lch and Rch (step S107). That is, Cc
The signal of h is added to the signals of Lch and Rch and output. If "C" is present and it is determined that "C" is small, the control unit turns on the switch SW2 and connects the switch SW7 to 2 (on the high-pass filter side) (step S108). On the other hand, if "C" is present and it is determined that "C" is large, the control unit
The switch SW2 is turned off, and the switch SW7 is connected to 1 (Cch side) (step S109).

Subsequently, the control unit controls the surround left speaker ("Sl") and the surround right speaker ("Sl").
r ”) and the size thereof are discriminated (step S110).
That is, the control unit determines whether or not “Sl” and “Sr” are present, and
If "l" and "Sr" are present, it is determined whether or not the frequency band of 100 Hz or less can be reproduced. The control unit is "Sl",
If it is determined that "Sr" is not present, the AC3 decoder 91 downmixes Slch and Srch into Lch and Rch (step S111). That is, Slch,
The Srch signal is added to the Lch and Rch signals and output. Further, when there are “Sl” and “Sr” and it is determined that “Sl” and “Sr” are small, the control unit turns on the switches SW4 and SW5 and sets the switches SW9 and SW10 to 2 ( It is connected to the high-pass filter) (step S112). On the other hand, "Sl", "S
If "r" is present and it is determined that "Sl" and "Sr" are large, the control unit turns off the switches SW4 and SW5 and sets the switches SW9 and SW10 to 1 (Sl).
ch, Srch side) (step S113).

In step S101 described above, "S
If it is determined that "W" does not exist, the control unit switches SW11.
Is connected to 1 (amplifier side) (step S114). That is, the control unit connects SW11 so that the signal that has passed through the low-pass filter F6 is supplied to the amplifier A7.
Next, the control unit determines the magnitude of "L" and "R" (step S115). When determining that "L" and "R" are large, the control unit turns off the switches SW1 and SW3 and sets the switches SW6 and SW8 to 1 (Lch, Rch).
Side) (step S116). In addition, "L",
Even if it is determined that “R” is small, the control unit switches SW
1 and SW3 are turned off, and switches SW6 and SW
8 is connected to 1 (step S117). This is because the low frequency component cannot be output from anywhere.

Subsequently, the control section determines whether or not "C" is present (step S118). When the control unit determines that there is no “C”, the AC3 decoder 91 sets Cch to Lch,
Down-mix with Rch (step S119).
On the other hand, when determining that “C” is present, the control unit turns off the switch SW2 and sets the switch SW7 to 1 (Cc).
(h side) is connected (step S120). Then, the control unit determines the presence or absence of "Sl" and "Sr" (step S121). If the control unit determines that “Sl” and “Sr” are not present, the AC3 decoder 91 causes Slch and Src to be output.
h is downmixed to Lch and Rch (step S122). When it is determined that “Sl” and “Sr” are present, the control unit turns off the switches SW4 and SW5, and sets the switches SW9 and SW10 to 1 (Slch, Sr).
to the rch side) (step S123).

By such an initial setting process, "L",
Each speaker of "R", "C", "Sl", "Sr" is 1
When the reproduction capability of 00 Hz or less is not provided, the low-pass components are cut by the high-pass filters F1 to F5, and the low-pass component signals are not supplied to the output side Lch, Cch, Rch, Slch, and Srch. And 100H
The low-frequency component signal of z or less is set to be supplied from the SWch on the output side via the low-pass filter F6. Also,
There is no "SW", "L" and "R" have a reproduction capability of 100 Hz or less, and "C", "Sl", and "S".
When “r” does not have a reproduction capability of 100 Hz or less, low-pass components are cut by the high-pass filters F2, F4, and F5, and the low-pass component signals are not supplied to the output side Cch, Slch, and Srch. . And 100 Hz
The following low-frequency component signals are set to be supplied from the Lch and Rch on the output side via the low-pass filter F6 and the amplifier A7.

Further, the AC3 decoder 91 sets Cch to L
When down-mixing to ch and Rch, the signal component of Cch is attenuated by −4.5 dB and distributed to Lch and Rch, and at the same time, a function of compressing so as not to clip is provided. Similarly, the AC3 decoder 91 uses Slch, S
When downmixing rch to Lch and Rch,
Compress so that it does not clip. Further, when there is no "SW", the AC3 decoder 91 sets the low frequency components to Lch, R.
It can also be assigned to ch. As a result, even in the case of town mixing, for example, audio reproduction can be performed so that the volume of dialogue does not change.

[0018]

The conventional signal processing circuit as described above performs the D setting by the initialization process shown in FIG.
Corresponding to the number of speakers and the low frequency reproduction capability connected to the VD player, the sub management 9 shown in FIG.
The connection of the two switches SW1 to SW11 is set. Then, when reproducing a digital signal encoded by the AC3 method, the signal processing circuit can reproduce an appropriate audio signal without being affected by the number of speakers or the like.

However, since the sub-management 92 shown in FIG. 7 corresponds only to the AC3 decoder 91,
When another decoder (DTS decoder 93 or the like) is used, the reproduced audio signal will be affected by the number of speakers and the like. This is the AC3 decoder 91
9 and other decoders (DTS decoder 93 etc.)
This is because there is a difference in function as shown in. That is, as shown in FIG. 9, according to each decoding method, the setting of the size of each speaker, the setting of the presence or absence of each speaker, and
Since there is a difference in functions such as signal compression at the time of downmix, if the decoder of the signal processing circuit is switched,
Depending on the number of speakers and the like, an appropriate audio signal cannot be reproduced.

For example, in the same DVD, the AC3 system and
When each digital signal encoded by the DVD audio multi-channel system is recorded, the user arbitrarily selects the decoder of the signal processing circuit to reproduce the audio signal. At this time, when the AC3 system decoder (AC3 decoder 91) is selected and played back, the number of speakers is less than the number of channels, or the low-frequency playback capability of the speaker is partially insufficient. However, as described above, the signal processing circuit outputs the components of all frequency bands in correspondence with the number of speakers and the like. However, if the decoder of the signal processing circuit is switched to the DVD audio multi-channel system in this state, unreproduced channels, frequency bands (low-frequency components), etc. will occur due to differences in the functions of the decoder. As described above, the conventional signal processing circuit has a problem in that, when the number of speakers and the low frequency reproduction capability are insufficient, the decoders are switched to cause a significant difference in reproduced audio signals. there were.

The present invention has been made in view of the above situation, and an appropriate audio signal can be reproduced even if the decoding system is switched in a state where the number of speakers and the low frequency reproduction capability are insufficient. The present invention relates to a signal processing circuit and a signal processing method that can be performed.

[0022]

In order to achieve the above object, a signal processing circuit according to a first aspect of the present invention provides a signal for supplying a multi-channel audio signal to a plurality of speakers corresponding to the channels. Decoding means, which is a processing circuit, receives a digital signal encoded by an arbitrary method, and decodes the signal into an audio signal of a predetermined number of channels corresponding to the encoding method of the input digital signal; Among the audio signals of each channel decoded by the means, a signal adding means for adding an audio signal of a predetermined channel to an audio signal of another channel according to the number of speakers constituting the channel, and decoding by the decoding means Audio signal and the audio signal added by the signal adding means. First filter means for cutting low-frequency components below a predetermined frequency band from the audio signal according to the low-frequency reproduction capability of the speaker corresponding to the channel, the audio signal decoded by the decoding means, and the signal Of the audio signals added by the adding means, a second filter that passes only low-frequency components below a predetermined frequency band from the audio signal corresponding to the channel whose low-frequency components have been cut by the first filter means. Means and are provided.

In order to achieve the above object, a signal processing circuit according to a second aspect of the present invention is a signal processing circuit for supplying a multi-channel audio signal to a plurality of speakers corresponding to channels. Fixed channel by inputting a digital signal encoded by an arbitrary method among digital signals encoded by a plurality of predetermined encoding methods and decoding the input digital signal by a corresponding method A decoder for generating a number of audio signals, and an audio signal of a predetermined channel is added to the audio signals of other channels, depending on the number of speakers of the audio signals of the respective channels decoded by the decoder. And an audio signal decoded by the decoder. A high-pass filter that cuts low-frequency components below a predetermined frequency band from the audio signals added by the adder according to the low-frequency reproduction capability of the speaker corresponding to the channel; and the audio decoded by the decoder. A low-pass filter that passes only a low-frequency component of a predetermined frequency band or less from the signal and the audio signal added by the adder and corresponding to the channel whose low-frequency component is cut by the high-pass filter; , Are provided.

In order to achieve the above object, a signal processing circuit according to a third aspect of the present invention is a signal processing circuit for supplying a multi-channel audio signal to a plurality of speakers corresponding to channels. Fixed channel by inputting a digital signal encoded by an arbitrary method among digital signals encoded by a plurality of predetermined encoding methods and decoding the input digital signal by a corresponding method A decoder for generating a number of audio signals, an adder for adding an audio signal of a predetermined channel to an audio signal of another channel, a high-pass filter for cutting low-frequency components below a predetermined frequency band from the audio signal of the predetermined channel, A low frequency component below a specified frequency band from the audio signal of a specified channel A low-pass filter that passes only the signal, a connection that switches the connection according to the number of speaker configurations corresponding to the channel, and supplies the audio signal decoded by the decoder to the adder; and a speaker corresponding to the channel. A connection is switched according to the low-frequency reproduction capability of the second audio signal, and the audio signal decoded by the decoder and the audio signal added by the adder are supplied to the high-pass filter.
Of the switch, the audio signal decoded by the decoder, and the audio signal added by the adder, the audio signal corresponding to the channel in which the low-pass component is cut by the high-pass filter is supplied to the low-pass filter. And a third switch for switching.

In order to achieve the above object, a signal processing method according to a third aspect of the present invention is a signal processing method for supplying a multi-channel audio signal to a plurality of speakers corresponding to channels. A decoding step of inputting a digital signal encoded by an arbitrary method and decoding into an audio signal of a predetermined number of channels according to the encoding method of the input digital signal, and the decoding step Among the audio signals of each channel, a signal adding step of adding an audio signal of a predetermined channel to an audio signal of another channel in accordance with the number of speakers constituting the channel, and an audio signal decoded in the decoding step. And from the audio signals added in the signal adding step, A low-frequency component below a predetermined frequency band according to the low-frequency reproduction capability of the speaker corresponding to the channel, the audio signal decoded in the decoding process, and the signal addition process. A second filtering step of passing only low-frequency components below a predetermined frequency band from the audio signals corresponding to the channels whose low-frequency components have been cut in the first filtering step among the added audio signals. And are provided.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION A signal processing circuit according to an embodiment of the present invention will be described below with reference to the drawings. The signal processing circuit is, for example, a circuit incorporated in a DVD player or the like, and is a circuit that supplies a multi-channel audio signal to a plurality of speakers corresponding to the channels.

FIG. 1 is a block diagram showing an example of the configuration of a signal processing circuit applied to the embodiment of the present invention.
As shown in the figure, this signal processing circuit comprises a multi-channel decoder 1 and a sub-management 2.

The multi-channel decoder 1 is, for example,
The decoder is capable of decoding digital signals encoded by the AC3 system, the DTS system, the MPEG multi-channel system, and the DVD audio multi-channel system. The multi-channel decoder 1 inputs streaming encoded digital signals,
By decoding the input digital signal by a corresponding method, Lch, Cch, Rch, Slch, Sr
Audio signals of 6 channels (5.1 channels) of ch and LFEch are generated. The multi-channel decoder 1 supplies the generated audio signal of each channel to the sub management 2.

As shown in FIG. 2, the sub-management 2 includes high-pass filters F1 to F5, low-pass filter F6, attenuators A1 to A6 and A8 to A14, an amplifier A7, switches SW1 to SW17, and an adder AD.
1 to AD6.

The high-pass filters F1 to F5 are adders A
The signals supplied via the D5, Cch, the adders AD6, Slch, and Srch, for example, cut low-frequency components of 100 Hz or less, and switch SW6 to SW10.
Supply to. The low-pass filter F6 cuts a high-frequency component of 100 Hz or higher from the signal added by the adder AD1 and supplies the signal to the switch SW11.

The attenuators A1 to A5 are, for example, -1.
5 dB attenuator, adder AD5, Cch,
The signals supplied via the adders AD6, Slch, and Srch are attenuated and supplied to the switches SW1 to SW5. Also, the attenuator A6 is, for example, -5 dB.
Attenuator, which attenuates the signal supplied via the LFEch and supplies the attenuated signal to the adder AD1. Further, the attenuator A8 is, for example, an attenuator of −4.5 dB, attenuates the signal supplied via Cch, and supplies the attenuated signal to the switch SW13. Also, the attenuator A9,
A10 is, for example, an attenuator of -4.5 db (attenuator A9 is an attenuator for phase inversion), attenuates the signal supplied via the adder AD4, and supplies it to the switches SW14 and SW15. Also, the attenuators A11 and A12 are, for example, 0 dB attenuators, and supply the signals supplied via the Slch and Srch to the switches SW16 and SW17. The attenuators A13 and A14 are, for example, 0 dB attenuators, and supply the signals supplied via the Lch and Rch to the adders AD5 and AD6. The amplifier A7 is, for example, a +10.5 dB amplifier, and has a switch SW11.
Amplifies the signal supplied through the adder AD2, A
Supply to D3.

The switches SW1 to SW5 turn on / off the connection between the attenuators A1 to A5 and the adder AD1. The switches SW6 to SW10 are adders AD5 and Cc.
h, the signal supplied via the adders AD6, S1ch, Srch or the signal passed through the high-pass filters F1 to F5 is selected and supplied to the adders AD2, AD3 and the like. The switch SW11 switches and supplies the signal that has passed through the low-pass filter F6 to either the amplifier A7 or the switch SW12. Switch SW12 is SW1
Either the signal supplied via 1 or the signal added by the adder AD1 is selected and supplied to the SWch. The switches SW13 to SW17 are attenuators A8 to A1.
The connection between 2 and the adders AD5 and AD6 is on / off controlled.

The adder AD1 includes attenuators A1 to A5.
(When the switches SW1 to SW5 are on) and the signals passed through the attenuator A6 are added and supplied to the low-pass filter F6 and the switch SW12. Also, adder A
D2 is the signal supplied via SW6 and the amplifier A
The signals passed through 7 are added and supplied to Lch. Also,
The adder AD3 receives the signal supplied via SW8 and
The signals that have passed through the amplifier A7 are added and supplied to Rch. Further, the adder AD4 adds the signal supplied via the Slch and the signal supplied via the Srch, and supplies the result to the attenuators A9 and A10. Further, the adder AD5 receives the signal that has passed through the attenuator A12 and
The signals supplied via the switches SW13, SW14 and SW16 are added and supplied to the high pass filter F1 and the attenuator A1. Further, the adder AD6 detects the signal passed through the attenuator A14, the switch SW13,
The signals supplied via SW15 and SW17 are added,
The high-pass filter F3 and the attenuator A3 are supplied.

The attenuators A8 to A10 described above are used.
Also, the adders AD4 to AD6 are used for signal processing the Dolby-encoded digital signals. Note that Dolby encoding is a standard of Dolby Laboratories, which encodes encoded 2-channel signals into Cch,
This is a method that can be decoded into signals of 4 channels of Lch, Rch, and Sch. As a specific standard, as shown in Equation 1, C, L, R, and S 4ch signals are L
It is defined as a 2ch signal of t and Rt.

[0035]

[Formula 1] Lt = L + 0.7C + 0.7S Rt = R + 0.7C-0.7S

In Expression 1, “0.7” is −
It represents 3 dB, and is a coefficient for equalizing the total sum of sound energies when reproduced on 2ch and when decoded and reproduced on 4ch. Further, the reference numeral represents the phase.

By the way, in the sub-management 2 shown in FIG. 2, C, L, R, Sl and Sr
5ch signal is defined as a 2ch signal of Lt and Rt.

[0038]

(2) Lt = L + 0.6C + 0.6 (Sl + Sr) Rt = R + 0.6C-0.6 (Sl + Sr)

In Expression 2, "0.6" is-
It represents 4.5 dB. Further, the reference numeral represents the phase.

The initial setting process for switching the connection of the switches SW1 to SW17 in the sub management 2 will be described below with reference to FIG. FIG. 3 shows switches SW1 to SW for appropriately changing the distribution of low-frequency components and the like in accordance with the number of speakers and the bass reproduction capability.
17 is a flowchart illustrating an initial setting process of switching the connection of No. 17. The initial setting process is executed by a control unit (microcomputer or the like) (not shown), and the connection settings of the switched switches SW1 to SW17 are held in the memory or the like. Further, the switch SW12 is connected to 1 (on the switch SW11 side) in a normal state.

First, the control section determines whether or not the digital signal decoded by the multi-channel decoder 1 is Dolby encoded (step S11). When determining that the Dolby encoding is performed, the control unit turns off SW16 and SW17 when the surround left speaker (“Sl”) and the surround right speaker (“Sr”) are not connected to the DVD player or the like (step S12). On the other hand, when it is determined that the Dolby encoding is not performed, the control unit determines if S1 and Sr do not exist, S
Turn off W13, SW14, and SW15 (step S
13).

Next, the control unit controls the subwoofer ("SW").
Whether or not is determined (step S14). The control unit
If it is determined that "W" is present, switch SW11 is set to 2 (SW
ch side) (step S15). That is, the signal that has passed through the low-pass filter F6 is output to the SWch.

Next, the control section determines the size of the left speaker ("L") and the right speaker ("R") (step S16). That is, "L" and "R" are 10
It is determined whether or not the frequency band below 0 Hz can be reproduced.
When the control unit determines that “L” and “R” are small (the frequency band of 100 Hz or less cannot be reproduced), the switch SW
1, SW3 is turned on, and switches SW6 and SW
8 is connected to 2 (high-pass filter side) (step S
17). On the other hand, when it is determined that “L” and “R” are large (the frequency band of 100 Hz or less can be reproduced), the control unit
The switches SW1 and SW3 are turned off, and the switches SW6 and SW8 are connected to 1 (Lch, Rch side) (step S18).

Subsequently, the control section determines the presence / absence of the center speaker ("C") and the size thereof (step S1).
9). That is, the presence / absence of “C” and 1 when “C” exists
It is determined whether or not the frequency band of 00 Hz or less can be reproduced. When the control unit determines that there is no "C", the switch S
W13 is turned on (step S20). That is, Cc
In order to add the signal of h to the signals of Lch and Rch, the switch SW13 is turned on. When it is determined that "C" is small and "C" is small, the control unit turns on the switch SW2 and turns on the switch SW7.
(High-pass filter side) (step S2)
1). On the other hand, if "C" is present and it is determined that "C" is large, the control unit turns off the switch SW2 and connects the switch SW7 to 1 (Cch side) (step S22).

Subsequently, the control unit determines the presence / absence of "Sl" and "Sr", and the size thereof (step S23). That is,
Whether or not "Sl" and "Sr" are present and whether or not a frequency band of 100 Hz or less can be reproduced is determined when "Sl" and "Sr" are present. When the control unit determines that there is no "Sl" or "Sr", the control unit SW13, SW14, SW15, or SW
16, SW17 is turned on (step S24). That is, when SW16 and SW17 are turned off in step S12 described above, SW13, SW14, and SW15 are turned on, and SW13 and SW15 are turned on in step S13 described above.
When SW14 and SW15 are turned off, SW16 and SW1
Turn on 7. Further, in the case where “Sl” and “Sr” are present and it is determined that “Sl” and “Sr” are small,
The controller turns on the switches SW4 and SW5 and connects the switches SW9 and SW10 to 2 (on the high-pass filter side) (step S25). On the other hand, "Sl",
When it is determined that “Sr” is present and “Sl” and “Sr” are large, the control unit switches SW4 and SW5.
Switch off and set switches SW9 and SW10 to 1
(Slch, Srch side) (step S2)
6).

In step S14 described above, "S
If it is determined that "W" does not exist, the control unit switches SW11.
Is connected to 1 (amplifier side) (step S27). That is, the signal that has passed through the low-pass filter F6 is amplified by the amplifier A7.
To be supplied to. Next, the control unit selects “L”,
The size of "R" is determined (step S28). When the control unit determines that “L” and “R” are large, the switch S
While turning off W1 and SW3, switches SW6 and S
Connect W8 to 1 (Lch, Rch side) (step S)
29). Even if it is determined that “L” and “R” are small,
The control unit turns off the switches SW1 and SW3, and connects the switches SW6 and SW8 to 1 (step S30). This is because the low frequency component cannot be output from anywhere.

Subsequently, the control section determines whether or not "C" is present (step S31). When determining that there is no "C", the control unit turns on SW13 (step S32). On the other hand, when it is determined that “C” is present, the control unit switches S
Turn off W2 and set switch SW7 to 1 (Cch
Side) (step S33).

Subsequently, the control section determines whether or not "Sl" and "Sr" are present (step S34). The control unit
If it is determined that "l" and "Sr" are not present, SW13 and SW1
4, SW15 or SW16, SW17 is turned on (step S35). That is, when SW16 and SW17 are turned off in step S12 described above, SW13,
When SW14 and SW15 are turned on, and when SW13, SW14, and SW15 are turned off in step S13 described above, SW16 and SW17 are turned on. In addition, "S
If it is determined that "l" and "Sr" are present, the control unit turns off the switches SW4 and SW5, and also switches SW
9, SW10 is connected to 1 (Slch, Srch side) (step S36).

By such initialization processing, "L",
Each speaker of "R", "C", "Sl", "Sr" is 1
When the reproduction capability of 00 Hz or less is not provided, the low-pass components are cut by the high-pass filters F1 to F5, and the low-pass component signals are not supplied to the output side Lch, Cch, Rch, Slch, and Srch. And 100H
The low-frequency component signal of z or less is set to be supplied from the SWch on the output side via the low-pass filter F6. Also,
There is no "SW", "L" and "R" have a reproduction capability of 100 Hz or less, and "C", "Sl", and "S".
When “r” does not have a reproduction capability of 100 Hz or less, low-pass components are cut by the high-pass filters F2, F4, and F5, and the low-pass component signals are not supplied to the output side Cch, Slch, and Srch. . And 100 Hz
The following low-frequency component signals are set to be supplied from the Lch and Rch on the output side via the low-pass filter F6 and the amplifier A7. Further, when there is no "C", "Sl", or "Sr", the connection of SW13 to SW17 is on / off controlled according to the decoding method, and the signals of Cch, Slch, Srch are downmixed to the signals of Lch, Rch. can do.

Thus, the multi-channel decoder 1
However, by decoding the input digital signal by a corresponding method, the Lch, Cch, Rch, and Sl are uniformly distributed.
Audio signals of six channels of ch, Srch, and LFEch are generated and supplied to the sub management 2. Then, the sub management 2 shown in FIG.
According to the initial setting process shown in (1), the number of speakers connected to the DVD player etc.
The connection of the switches SW1 to SW17 is set. Therefore, when reproducing a digital signal encoded by an arbitrary method, the signal processing circuit can appropriately generate an audio signal without being affected by the number of speakers or the like. As a result, it is possible to reproduce an appropriate audio signal even if the decoding system is switched in a state where the number of speakers and the low frequency reproduction capability are insufficient.

Further, the sub management 2 shown in FIG.
Can also output the signals of all channels through in accordance with the DVD audio standard. That is, S
Turn off W1-SW5, connect SW6-SW10 to 1, connect SW12 to 2, and SW13-SW1
By turning off 7 and setting the attenuator A6 to 0 dB, the input side Lch, Cch, Rch, S
The Lch, Srch, and LFEch signals are directly output to the output side Lch, Cch, Rch, Slch, Srch,
It can be supplied to SWch.

In the above-described embodiment, in the initial setting process shown in FIG. 3, Dolby encoding is discriminated (step S11), setting for performing Dolby encoding (step S12) and setting for not performing Dolby encoding. Although (step S13) is performed, whether or not Dolby encoding is performed may be fixed and these settings and the like may be omitted.

In the above-described embodiment, in the sub-management 2 shown in FIG. 2, the adders AD5 and AD6 simply add the signals, so that the signals of the DVD audio multi-channel system (PCM multi-channel) are added. At this time, the signal may be clipped.
In this case, it is possible to avoid the signal clipping by reducing the attenuation values of the attenuators A8 to A14 with the same ratio, for example, by -10 dB. In addition, the adder AD2
Similarly, in AD3, by reducing the attenuation values of the attenuators A8 to A14 and the amplifier A7, it is possible to avoid the signal clipping. In this case, the signal level is lowered, but for example, when a DAC (digital-analog converter) is provided on the output side, the signal level may be increased and then returned to the original level after being converted into an analog signal.

Further, in order to avoid a clip at the time of downmixing, the target signal may be compressed by the sub management 2. Specifically, as shown in FIG. 4, a circuit surrounded by a broken line h is a sub management 2
Add to. That is, the compressors C1 and C2 and the amplifiers A15 and 16 are added to the output sides of the adders AD2 and AD3. The compressors C1 and C2 are adders AD
2, the signals added in AD3 are compressed only by the amount by which only the signals higher than the average reference level are clipped without compressing the signals lower than the average reference level. This means that the average reference level of the signal before compression is -20.
Since it is about dB, when the compressors C1 and C2 are added, in the adders AD2, AD3, AD5 and AD6,
Attenuator A8-A before the signal is clipped
It is necessary to reduce the attenuation value of 14 by the same ratio. For example, −
If it is lowered by 20 dB, the average reference level is -40d.
It becomes B. By the way, the compressors C1 and C2 have, for example, input / output characteristics as shown in FIG.
The signal at point B is compressed as shown by the curve connecting points A and C. Then, at the point C, the input is 0 dB and the output is -20 dB. Therefore, the dynamic range can be 20 dB. Then, in the amplifiers A15 and 16,
The signal level is amplified by about +20 dB.

As described above, the sub-management 2 shown in FIG. 4 includes the compressors C1 and C2, the amplifier A15,
By 16, the average reference level of the signal is maintained even when the signal is downmixed, as when the signal is not downmixed. Therefore, even when downmixing is performed, it is possible to reproduce without changing the volume of the dialogue of the movie. Also, since the dynamic range does not increase, even when the output signal is supplied to the amplifier, the signal is not clipped by the amplifier.

[0056]

As described above, according to the present invention,
Even when the decoding method is switched in a state in which the number of speakers and the low frequency reproduction capability are insufficient, an appropriate audio signal can be reproduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of a configuration of a signal processing circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an example of a specific configuration of sub-management.

FIG. 3 is a flowchart illustrating an initial setting process according to the embodiment of the present invention.

FIG. 4 is a circuit diagram showing an example of another configuration of sub-management.

FIG. 5 is a schematic diagram for explaining input / output characteristics of a compressor.

6A and 6B are block diagrams showing an example of a configuration of a conventional signal processing circuit.

FIG. 7 is a circuit diagram showing an example of a specific configuration of conventional sub-management.

FIG. 8 is a flowchart for explaining an initial setting process in conventional sub management.

[Fig. 9] Fig. 9 is a diagram for describing a difference in function between the decoders.

[Explanation of symbols]

1 multi-channel decoder 2 sub management F1 to F5 high pass filter F6 low pass filter A1 to A6, A8 to A14 Attenuator A7 amplifier SW1 to SW17 switches AD1 to AD6 adder

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Claims (4)

[Claims] 1. A signal processing circuit for supplying a multi-channel audio signal to a plurality of speakers corresponding to a channel, wherein a digital signal encoded by an arbitrary method is input, and the input digital signal Decoding means for decoding an audio signal of a predetermined number of channels, corresponding to the encoding method, and among the audio signals of the respective channels decoded by the decoding means, according to the number of speakers constituting the channel, The audio signal of a predetermined channel,
From the audio signal decoded by the decoding means and the audio signal added by the signal adding means, the signal adding means for adding to the audio signal of another channel, according to the low-frequency reproduction capability of the speaker corresponding to the channel, First filter means for cutting low-frequency components below a predetermined frequency band, audio signals decoded by the decoding means, and audio signals added by the signal adding means by the first filter means A signal processing circuit, comprising: a second filter unit that passes only a low-frequency component below a predetermined frequency band from an audio signal corresponding to a channel in which the low-frequency component is cut. 2. A signal processing circuit for supplying a multi-channel audio signal to a plurality of speakers corresponding to channels, the digital signal being encoded by a plurality of predetermined encoding methods. A decoder that generates an audio signal of a fixed number of channels by inputting a digital signal encoded by an arbitrary method and decoding the input digital signal by a corresponding method, and a decoder for each channel decoded by the decoder. Among the audio signals, an adder that adds an audio signal of a predetermined channel to an audio signal of another channel according to the number of speaker configurations corresponding to the channel, an audio signal decoded by the decoder, and the adder From the added audio signals,
A high-pass filter that cuts low-frequency components below a predetermined frequency band according to the low-frequency reproduction capability of the speaker corresponding to the channel, an audio signal decoded by the decoder, and an audio signal added by the adder. Of which
A low-pass filter that passes only a low-frequency component below a predetermined frequency band from an audio signal corresponding to a channel whose low-frequency component has been cut by the high-pass filter, a signal processing circuit. 3. A signal processing circuit for supplying a multi-channel audio signal to a plurality of speakers corresponding to channels, the digital signal being encoded by a plurality of predetermined encoding methods. Input a digital signal encoded by any method and decode the input digital signal by the corresponding method to generate a fixed number of channels of audio signals and a predetermined channel of audio signals of other channels. An adder that adds to the audio signal, a high-pass filter that cuts low-frequency components below a predetermined frequency band from the audio signal of a predetermined channel, and a low-pass component below a predetermined frequency band from the audio signal of a predetermined channel Low-pass filter and switch corresponding to the channel The connection is switched according to the number of the constituent speakers, and the connection is switched according to the low-frequency reproduction capability of the speaker corresponding to the channel and the first switch for supplying the audio signal decoded by the decoder to the adder. A second switch for supplying the audio signal decoded by the decoder and the audio signal added by the adder to the high-pass filter, the audio signal decoded by the decoder, and the adder added by the adder Of the audio signal
A signal processing circuit comprising: a third switch that supplies an audio signal corresponding to a channel whose low-pass component is cut by the high-pass filter to the low-pass filter. 4. A signal processing method for supplying a multi-channel audio signal to a plurality of speakers corresponding to channels, wherein a digital signal encoded by an arbitrary method is input, and the input digital signal Depending on the encoding method, a decoding step of decoding into a predetermined number of channels of audio signals, and among the audio signals of each channel decoded in the decoding step, depending on the number of speaker configurations corresponding to the channels , A signal adding step of adding an audio signal of a predetermined channel to an audio signal of another channel, the audio signal decoded in the decoding step, and the audio signal added in the signal adding step, corresponding to a channel Depending on the low-frequency reproduction capability of the speaker, the specified frequency band Of the audio signals decoded in the decoding step and the audio signals added in the signal adding step, the first filtering step of cutting the low-frequency components below is performed in the first filtering step. A second filtering step of allowing only low-frequency components below a predetermined frequency band to pass from an audio signal corresponding to a channel whose frequency components are cut off; and a signal processing method.