Abstract:
The present invention provides a method to convert the conventional two-channel uncoded audio system into multichannel system. There is no coding/decoding procedure in the invention, but just process the phases of the original two audio channels to provide different audio sources for surrounding distribution and achieve the best effect of reproducing the original audios. The present invention also provides an audio processor for implementing the method.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a method for converting a two-channel audio system into a multichannel audio system and to an audio processor thereof, and more particularly to a method of processing the phase of the original audio signal to achieve the object. 
   BACKGROUND OF THE INVENTION 
   Multichannel Dolby system and the like are very popular in current audio systems. Those systems emphasize that the original multichannel audios are first encoded into two-channel audios for transmitting, and then returned to the original multichannel audios by a specially designed decoder for playing. 
   However, if a system has audios of only two channels, using the aforementioned multichannel systems for processing will cause misleading operation and distortion. 
   Therefore, if a system is to convert a two-channel audio system into a multichannel audio system, a special design is required. 
   OBJECT OF THE INVENTION 
   It is therefore an object of the present invention to provide a method to convert a two-channel audio system into multichannel audio system and an audio processor thereof. The original two-channel audios are not coded and decoded, but just the phase of the original audio signals is processed to achieve the object. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows schematically the surrounding distribution of converting a two-channel audio system into multichannel audio system according to the present invention. 
       FIG. 2  shows schematically a circuit diagram of the audio processor according to the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , which shows schematically the surrounding distribution of converting a two-channel audio system into multichannel audio system according to the present invention. An audience  1  is in the center, 9 audio equipments are distributed surroundingly as CT, L, CRL, RL, RCT, RR, CRR, R and SUB respectively. 
   The conventional two-channel audios L in  (left channel audio) and R in  (right channel audio) are inputted into each of the 9 audio equipments, and are processed by a specially designed audio processor  2  (see  FIG. 2 ) for outputting special outputs. 
   The special outputs of the 9 audio equipments are as below:
     1. CT: L in +R in      2. L: L in      3. CRL: 2L in −(½)R in      4. RL: 2L in −R in      5. RCT: L in +R in      6. RR: 2R in −L in      7. CRR: 2R in −(½)L in      8. R: R in      9. SUB: (L in +R in )×LPF   

   L in  represents left channel audio, while R in  represents right channel audio, and LPF is a low-pass filter. The audio effects in the spaces between each two of the 9 audio equipments are 2L in +R in , 3L in −(½)R in , 4L in −(1+½)R in , 3L in , 3R in , 4R in −(1+½)L in , 3R in −(½)L in , 2R in +L in  and 2L in +2R in  respectively as shown. 
   Referring to  FIG. 2 , which shows schematically a circuit diagram of the audio processor according to the present invention, in which the left channel audio L in  and the right channel audio R in  are inputted respectively into operational amplifiers OP 1  and OP 2  through some resistors. A control signal CTRL in the center of the circuit diagram is used to control four switches SW 1 , SW 2 , SW 3  and SW 4 . An inverter IN is also included as shown. 
   When the control signal CTRL is low, SW 1  will open and SW 2  will close, the right channel audio R in  can&#39;t be inputted into OP 1 , so OP 1  is only influenced by the left channel audio L in . According to the principle of the operational amplifier, the voltage level of L out  at B must be the voltage level at A×(R 3 +R 4 )/R 3 , while the voltage level at A is L in ×R 2 /(R 1 +R 2 ) according to the circuit diagram, thus L out =L in ×R 2 /(R 1 +R 2 )×(R 3 +R 4 )/R 3 =L in  ∘ 
   When the control signal CTRL is high, SW 1  will close and SW 2  will open, the right channel audio R in  will be inputted into the “−” terminal of OP 1  through resistor R 3 . According to the principle of the operational amplifier, the right channel audio R in  will generate an output of R in ×(−)R 4 /R 3 =−½R in  at B, while the left channel audio L in  will generate an output of L in  at B (as described above), thus the composition voltage of L out  at B is L in −½R in  ∘ 
   In the circuit of the audio processor stated above, since it is designed by letting R 1 =R 4  and R 2 =R 3 , the left channel audio L in  can be reproduced at L out . If we need to demonstrate the influence of the right channel audio R in , it is only necessary to change the voltage level of the control signal CTRL, and the user can clearly distinguish the effect of adding the right channel audio R in  ∘ 
   In the circuit of the audio processor stated above, L out =L in , but if we change the ratio between R 1  and R 2 , the coefficient before L in  in L out  can be changed; and if we change the ratio between R 3  and R 4 , the coefficient before R in  in L out  can be changed. 
   Similarly, when the control signal CTRL is low, SW 3  will open and SW 4  will close, the left channel audio L in  can&#39;t be inputted into OP 2 , so OP 2  is only influenced by the right channel audio R in . According to the principle of the operational amplifier, the voltage level of R out  at D must be the voltage level at C×(R 7 +R 8 )/R 7 , while the voltage level at C is R in ×R 6 /(R 5 +R 6 ) according to the circuit diagram, thus R out =R in ×R 6 /(R 5 +R 6 )×(R 7 +R 8 )/R 7 =R in . 
   When the control signal CTRL is high, SW 3  will close and SW 4  will open, the left channel audio L in  will be inputted into the “−” terminal of OP 2  through resistor R 7 . According to the principle of the operational amplifier, the left channel audio L in  will generate an output of L in ×(−)R 8 /R 7 =−½L in  at D, while the right channel audio R in  will generate an output of R in  at D (as described above), thus the composition voltage of R out  at D is R in −½L in . 
   In the circuit of the audio processor stated above, since it is designed by letting R 5 =R 8  and R 6 =R 7 , the right channel audio R in  can be reproduced at R out . If we need to demonstrate the influence of the left channel audio L in , it is only necessary to change the voltage level of the control signal CTRL, and the user can clearly distinguish the effect of adding the left channel audio L in . 
   In the circuit of the audio processor stated above, R out =R in , but if we change the ratio between R 5  and R 6 , the coefficient before R in  in R out  can be changed, and if we change the ratio between R 7  and R 8 , the coefficient before L in  in R out  can be changed. 
   Referring to  FIG. 1  again, it is found that each of the outputs of the 9 audio processors has different coefficients before L in  and R in , this is because we change the ratio between related resistors. 
   The operational amplifiers, the voltage dividers, the switches, the resistors and the inverter in the audio processor of the present invention can be implemented by the digital simulation techniques of computer software. 
   The spirit and scope of the present invention depends only upon the following Claims, and is not limited by the above embodiment.