Abstract:
An audio apparatus, which is compatible with multi-channel audio sources, is capable of achieving reproduction without sound drop-out even in use with only two speakers. The audio apparatus includes an audio mixing circuit that inputs an L audio signal, R audio signal, C audio signal, SL audio signal, SR audio signal and SW audio signal, respectively mixes the C audio signal, SL audio signal, SW audio signal with the L audio signal in a predetermined ratio and mixes the C audio signal, SR audio signal, SW audio signal with the R audio signal in a predetermined ratio; and an audio signal conditioning circuit that inputs the output signal of the audio mixing circuit and adjusts the signal waveform thereof.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an audio apparatus compatible with multi-channel audio sources.  
         [0003]     2. Description of the Related Art  
         [0004]     In recent years, an audio apparatus compatible with multi-channel (for example, so-called 5.1 channel) audio sources used in, for example, a home theatre has been commercialized. Such an audio apparatus makes it possible to obtain an effect like that of a theatre or concert hall by arranging speakers on the left and right and centrally in front of the audience and on the left and right to the rear of the audience (see, for example, Laid-open Japanese Patent Application No. 2002-345097). A 5.1 channel audio apparatus, like the conventional stereo audio apparatus, processes stereo audio signals including an audio signal of a left channel (L) for the front left-hand speaker and an audio signal of a right channel (R) for the front right-hand speaker with respect to the audience. In addition, such a 5.1 apparatus processes surround audio signals including an audio signal of the center channel (C) for the speaker at the front in the middle, an audio signal of the surround left channel (SL) for the speaker to the rear on the left-hand side, an audio signal of the surround right channel (SR) for the speaker to the rear on the right-hand side and an audio signal of a sub-woofer channel (SW) for a speaker that outputs in deep bass audio bands (for example, bass guitar or drum sounds). Audio sources corresponding to the performed content are assigned to these respective channels. Also, in a DVD optical disc, the audio sources of these multiple channels are recorded and, typically, the audio apparatus for these multiple channels performs reproduction thereof.  
         [0005]     The block diagram of  FIG. 4  shows the output section of a conventional audio apparatus compatible with 5.1 channel audio sources. This audio apparatus  101  includes an audio signal conditioning circuit  103 , power amplifiers  104 L,  104 R,  104 C,  104 SL,  104 SR,  104 SW, speakers  105 L,  105 R,  105 C,  105 SL,  105 SR and  105 SW. The audio signal conditioning circuit  103  inputs the L audio signal, R audio signal, C audio signal, SL audio signal, SR audio signal, and SW audio signal respectively from the input terminals L, R, C, SL, SR and SW into the LinA terminal, RinA terminal, CinA terminal, SLinA terminal, SRinA terminal and SWinA terminal of the audio signal conditioning circuit  103 . Adjustment of the waveform of the audio signals, i.e., adjustment of for example the quantity of sound, treble and bass is then performed and the signals are then respectively output from the LoutA terminal, RoutA terminal, CoutA terminal, SLoutA terminal, SRoutA terminal and SWoutA terminal of the audio signal conditioning circuit  103 .  
         [0006]     Power amplifiers  104 L,  104 R,  104 C,  104 SL,  104 SR and  104 SW then input the respective audio signals from the LoutA terminal, RoutA terminal, CoutA terminal, SLoutA terminal, SRoutA terminal and SWoutA terminal of the audio signal conditioning circuit  103  and thereby drive the speakers  105 L,  105 R,  105 C,  105 SL,  105 SR, and  105 SW.  
         [0007]     In this way, with an audio apparatus having multi-channel audio sources, the audience can enjoy an effect like that of a theatre or concert hall. However, depending on the environment of use of this audio apparatus (such as, for example, the size of the room), speakers could sometimes only be arranged in front of and to left and right of an audience in the same way (in the case of a stereo set) as in the case of a conventional stereo audio apparatus, without providing a very large number of speakers. In this case, as shown in  FIG. 5 , only the LoutA terminal and RoutA terminal of the audio signal conditioning circuit  103  are connected with the power amplifiers  104 L,  104 R, and stereo audio signals including an L audio signal and R audio signal from the speakers  105 L and  105 R are thereby converted to sound, and then output.  
         [0008]     Consequently, the audio signals of the CoutA terminal, SLoutA terminal, SRoutA terminal and SWoutA terminal of the audio signal conditioning circuit  103  are not output from the speakers, so the sound that is assigned to the C audio signal, SL audio signal, SR audio signal and SW audio signal drops out and cannot be heard by the audience.  
       SUMMARY OF THE INVENTION  
       [0009]     In order to overcome the problems described above, preferred embodiments of the present invention provide an audio apparatus wherein reproduction of multi-channel audio sources can be achieved without drop-out, both for multi-channel audio sources where a speaker is connected to each audio source and where the number of connected speakers is less than the number of audio sources.  
         [0010]     An audio apparatus according to a preferred embodiment of the present invention includes an audio mixing circuit that inputs a left channel audio signal, a right channel audio signal, a center channel audio signal, a surround left channel audio signal, a surround right channel audio signal and a sub-woofer channel audio signal and that is capable of delivering output by respectively mixing a center channel audio signal, a surround left channel audio signal, and a sub-woofer channel audio signal with a left channel audio signal in a predetermined ratio, a center channel audio signal, a surround right channel audio signal, and a sub-woofer channel audio signal with a right channel audio signal in a predetermined ratio; an audio signal conditioning circuit that inputs the output signal of the audio mixing circuit and adjusts the signal waveforms; a power amplifier section including a plurality of power amplifiers that amplify audio signals whose signal waveform has been adjusted; and a speaker section including a plurality of speakers driven by the amplified audio signals.  
         [0011]     Preferably, the audio mixing circuit of this audio apparatus is capable of selecting one of a condition in which output is delivered after mixing and a condition in which output is delivered without mixing the left channel audio signal, right channel audio signal, center channel audio signal, surround left channel audio signal, surround right channel audio signal and sub-woofer channel audio signal.  
         [0012]     With the audio apparatus according to preferred embodiments of the present invention, since the audio mixing circuit is provided, even if a speaker is connected with each audio source or even if, for example, only two speakers are connected such that the number of connected speakers is less than the number of audio sources, reproduction can be achieved without dropping out of the audio sources of the multiple channels, making it possible to enjoy an effect like that of a theatre or concert hall.  
         [0013]     Other features, elements, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a block diagram of a full set of an audio apparatus according to a preferred embodiment of the present invention.  
         [0015]      FIG. 2  is a block diagram of a stereo set of an audio apparatus according to a preferred embodiment of the present invention.  
         [0016]      FIG. 3  is a circuit diagram of an audio mixing circuit according to a preferred embodiment of the present invention.  
         [0017]      FIG. 4  is a block diagram of a full set of an audio apparatus according to the background art.  
         [0018]      FIG. 5  is a block diagram of a stereo set of audio apparatus according to the background art. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0019]     Preferred embodiments of the present invention will now be described with reference to the drawings.  FIG. 1  and  FIG. 2  are block diagrams of an audio apparatus  1  compatible with multi-channel audio sources according to a preferred embodiment of the present invention. This audio apparatus  1  is preferably 5.1 channel audio apparatus. One of the unique features of the audio apparatus  1  is that an audio mixing circuit  2  is arranged upstream of the audio signal conditioning circuit  3 . The audio signal conditioning circuit  3  is a circuit that is preferably substantially the same as the audio signal conditioning circuit  103 .  
         [0020]     Specifically, in the case of a full set (home theatre set) shown in  FIG. 1 , this audio apparatus  1  includes an audio mixing circuit  2 , audio signal conditioning circuit  3 , power amplifier section  4 , more specifically, power amplifiers  4 L,  4 R,  4 C,  4 SL,  4 SR,  4 SW and a speaker section  5 , more specifically, speakers  5 L,  5 R,  5 C,  5 SL,  5 SR and  5 SW. On the other hand, in the case of a stereo set shown in  FIG. 2 , the audio apparatus  1  includes an audio mixing circuit  2 , an audio signal conditioning circuit  3 , a power amplification section  4  including power amplifiers  4 L,  4 R, and a speaker section  5  including speakers  5 L and  5 R.  
         [0021]     In this audio mixing circuit  2 , a stereo audio signal including a left channel (L) audio signal and right channel (R) audio signal is input from the respective input terminals L, R to the LinM terminal and RinM terminal; and a surround audio signal including a center channel (C) audio signal, surround left channel (SL) audio signal, surround right channel (SR) audio signal and sub-woofer channel (SW) audio signal is input from the respective input terminals C, SL, SR, SW to the CinM terminal, SLinM terminal, SRinM terminal and SWinM terminal. Processing of the stereo audio signal and surround audio signal is controlled by the mixing control circuit  20 , described in detail below. This mixing control circuit  20  has an SinM terminal as input terminal, and has an inversion output terminal and non-inversion output terminal. Changeover is effected between the condition in which the SinM terminal is grounded and the condition in which the SinM terminal is connected to the power source Vcc, via an external changeover switch (not shown).  
         [0022]     First of all, in the case of a full set, as shown in FIG.  1 , the audio mixing circuit  2  is arranged such that the SinM terminal, i.e. the input terminal of the mixing control circuit  20 , is grounded. In this way, the audio signals that are input to the LinM terminal, RinM terminal, CinM terminal, SLinM terminal, SRinM terminal and SWinM terminal are respectively directly output from the LoutM terminal, RoutM terminal, CoutM terminal, SLoutM terminal, SRoutM terminal and SWoutM terminal.  
         [0023]     The audio signal conditioning circuit  3  performs the adjustment of the waveform, i.e. the adjustment of, for example, the amount of sound, treble and bass, of the audio signals that are input from the LoutM terminal, RoutM terminal, CoutM terminal, SLoutM terminal, SRoutM terminal and SWoutM terminal of the audio mixing circuit  2  into the respective LinA terminal, RinA terminal, CinA terminal, SLinA terminal, SRinA terminal and SWinA terminal, and respectively outputs these audio signals on which waveform adjustment has been performed from the LoutA terminal, RoutA terminal, CoutA terminal, SLoutA terminal, SRoutA terminal and SWoutA terminal.  
         [0024]     The power amplifiers  4 L,  4 R,  4 C,  4 SL,  4 SR,  4 SW of the power amplifier section  4  input the audio signals that have respectively been adjusted in waveform from the LoutA terminal, RoutA terminal, CoutA terminal, SLoutA terminal, SRoutA terminal and SWoutA terminal of the audio signal conditioning circuit  3  and amplify these, and drive the speakers  5 L,  5 R,  5 C,  5 SL,  5 SR and  5 SW of the speaker section  5  via the amplified audio signals.  
         [0025]     In contrast, in the case of a stereo set, as shown in  FIG. 2 , the SinM terminal, i.e., the input terminal of the mixing circuit  20  is connected with the power source Vcc. In this way, the audio signals that are input to the CinM terminal, SLinM terminal and SWinM terminal are mixed with the audio signal that is input to the LinM terminal, the audio signals that are input to the CinM terminal, SRinM terminal and SWinM terminal are mixed with the audio signal that is input to the RinM terminal, and are output as a stereo audio signal from the LoutM terminal and RoutM terminal. Audio signals from the CoutM terminal, SLoutM terminal, SRoutM terminal and SWoutM terminal are not output (the outputs are in a no-signal condition).  
         [0026]     The audio signal conditioning circuit  3  performs adjustment of the waveform of the audio signals that are input to the respective LinA terminal and RinA terminal from the LoutM terminal and RoutM terminal of the audio mixing circuit  2 , and respectively outputs these audio signals whose waveforms have been adjusted from the LoutA terminal and RoutA terminal. Also, in the case of a stereo set too, just as in the case of a full set, the CinA terminal, SLinA terminal, SRinA terminal and SWinA terminal of the audio signal conditioning circuit  3  are respectively connected with the CoutM terminal, SLoutM terminal, SRoutM terminal and SWoutM terminal of the audio mixing circuit  2 .  
         [0027]     Also, the power amplifiers  4 L,  4 R of the power amplification section  4  input and amplify the audio signals that have been respectively subjected to waveform adjustment from the LoutA terminal and RoutA terminal of the audio signal conditioning circuit  3  and the speakers  5 L and  5 R of the speaker section  5  are driven by the amplified audio signal. The CoutA terminal, SLoutA terminal, SRoutA terminal and SWoutA terminal of this audio signal conditioning circuit  3  are not connected to anything.  
         [0028]     Next, the internal circuitry of the audio mixing circuit  2  will be described with reference to  FIG. 3 .  
         [0029]     One end of the resistor  21  is connected with the LinM terminal and one end of the resistor  23  is connected with the SLinM terminal and one terminal of the switch  47  is connected therewith. The control terminal of the switch  47 , like the control terminals of the respective switches  48  to  50 , to be described later, is connected with the inversion output terminal of the mixing control circuit  20 . The other terminal of the switch  47  is connected with the SLoutM terminal. The other end of the resistor  23  is connected with one terminal of the switch  41 . The control terminal of the switch  41 , like the control terminals of the respective switches  42  to  46 , to be described later, is connected with the non-inversion output terminal of the mixing control circuit  20 . The other terminal of the switch  41  and the other end of the resistor  21  are mutually connected and connected to the one end of the resistor  22  and the inversion input terminal of an operational amplifier  11 . The non-inversion input terminal of the operational amplifier  11 , like the non-inversion input terminal of the operational amplifiers  12  to  14 , to be described later, is connected with a reference voltage Vref. The output terminal of the operational amplifier  11  and the other end of the resistor  22  are mutually connected and connected with one end of the resistor  24 . Also, one end of the resistor  26  and one end of the resistor  33  are connected with the CinM terminal and connected with one terminal of the switch  49 . The other terminal of the switch  49  is connected with the CoutM terminal. The other end of the resistor  26  is connected with one terminal of the switch  42  and the other end of the resistor  33  is connected with one terminal of the switch  45 . One end of the resistor  27  and one end of the resistor  34  are connected with the SwinM terminal and connected with one terminal of the switch  50 . The other terminal of the switch  50  is connected with the SWoutM terminal. The other end of the resistor  27  is connected with one terminal of the switch  43  and the other end of the resistor  34  is connected with one terminal of the switch  46 . Also, the other end of the resistor  24  and the other terminals of the respective switches  42  and  43  are mutually connected and connected with one end of the resistor  25  and with the inversion input terminal of the operational amplifier  12 . The output terminal of the operation amplifier  12  and the other end of the resistor  25  are mutually connected and connected with the LoutM terminal. The resistors  21  and  22  and resistors  24  and  25  are set to respectively equal resistances.  
         [0030]     One end of the resistor  28  is connected with the RinM terminal and one end of the resistor  30  is connected with the SRinM terminal and with one terminal of the switch  48 . The other terminal of the switch  48  is connected with the SRoutM terminal. The other end of the resistor  30  is connected with one terminal of the switch  44 . The other terminal of the switch  44  and the other end of the resistor  28  are mutually connected and connected with one end of the resistor  29  and the inversion input terminal of the operational amplifier  13 . The output terminal of the operational amplifier  13  and the other end of the resistor  29  are mutually connected and connected with one end of the resistor  31 . The other end of the resistor  31  and the respective other terminals of the switches  45  and  46  are mutually connected and connected with one end of the resistor  32  and the inversion input terminal of the operational amplifier  14 . The output terminal of the operational amplifier  14  and the other end of the resistor  32  are mutually connected and connected with the RoutM terminal. The resistors  28  and  29  are set to and resistors  31  and  32  are set to respectively equal resistances.  
         [0031]     Next, the operation will be described. First of all, in the case of a full set, the SinM terminal is grounded, so low level is output from the non-inversion output terminal of the mixing control circuit  20  and high-level is output from the inversion output terminal. Consequently, the switches  41  to  46  do not conduct, but the switches  47  to  50  do conduct. Consequently, the audio signal that is input to the LinM terminal is inverted by the inversion amplifier constituted by the resistors  21  and  22  and operational amplifier  11 , and is further inverted by the inversion amplifier constituted by the resistors  24  and  25  and the operational amplifier  12 . Since the resistors  21  and  22  and the resistors  24  and  25  are set to respectively equal resistances, the audio signal that is output from the LoutM terminal is substantially equal to the audio signal that is input to the LinM terminal. Likewise, the audio signal that is output from the RoutM terminal is substantially equal to the audio signal that is input to the RinM terminal. Also, the audio signals that are input to the CinM terminal, SLinM terminal, SRinM terminal and SWinM terminal are output through the switches  47  to  50  to the CoutM terminal, SLoutM terminal, SRoutM terminal and SWoutM terminal.  
         [0032]     In contrast, in the case of a stereo set, the SinM terminal is connected with the power source Vcc, so high level is output from the non-inversion output terminal of the mixing control circuit  20  and low level is output from the inversion output terminal. Consequently, the switches  41  to  46  conduct, but the switches  47  to  50  do not conduct. Consequently, the audio signal that is input to the LinM terminal is mixed with the audio signal that is input to the SLinM terminal in a predetermined ratio determined by the resistor  23  and is inverted and this inverted signal is mixed with the audio signals that are input to the CinM terminal and the SwinM terminal in respective predetermined ratios determined by the resistors  26  and  27  and is further inverted before being output from the LoutM terminal. Likewise, the audio signal that is input to the RinM terminal is mixed in predetermined ratios with the audio signals that are input at the SRinM terminal, CinM terminal and SWinM terminal, before being output from the RoutM terminal. Also, since the switches  47  to  50  do not conduct, the outputs of the CoutM terminal, SLoutM terminal, SRoutM terminal and SWoutM terminal are in a no-signal condition.  
         [0033]     As described above, in the case of a full set shown in  FIG. 1 , by arranging speakers at each audio source, specifically, at the left and right and at the center at the front, and at the left and right at the rear, the audience can enjoy sound with the characteristic effects specific to multi-channel audio sources, and, in the case of a stereo set shown in  FIG. 2 , by arranging two speakers, for example, only on the left and right at the front, the audience can enjoy sound in which no audio sources of the multiple channels are lost.  
         [0034]     It should be noted that the audio mixing circuit  2  is not restricted to that of the above-described preferred embodiments but could be implemented by other circuits. Also, the changeover switch that changes over connections of the SinM terminal of the mixing control circuit  20  with the ground or the power source Vcc may be arranged to effect changeover after automatic detection of the number of power amplifiers, i.e. the number of speakers. Also, although the mixing control circuit  20  distinguishes between a full set and stereo set by the voltage of the SinM terminal, it could be arranged for the mixing control circuit  20  to be provided with a register in which data for distinguishing these is written.  
         [0035]     Also, while it may be envisioned that the audio mixing circuit  2  could be substituted by DSP, since DSP is expensive, costs could be lowered by this audio mixing circuit  2  constructed by comparatively simple analog circuits. Also, the audio apparatus can be reduced in cost and reduced in size by forming the audio mixing circuit  2  and the audio signal conditioning circuit  3  in the form of a single chip on the same semiconductor substrate.  
         [0036]     Also, the present invention is not restricted to the preferred embodiments described above and various design modifications are possible within the scope of the items set out in the claims. For example, although the above description was given for the case of a 5.1 channel audio apparatus  1 , the present invention could of course be applied to a 6.1 channel or 7.1 channel audio apparatus in which even more audio sources (for example additional surround background sound) are provided.  
         [0037]     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.