Patent Publication Number: US-2006008094-A1

Title: Wireless multi-channel audio system

Description:
BACKGROUND OF INVENTION  
      1. Field of the Invention  
      The present invention relates to an audio system, and more particularly to a wireless, multi-channel audio system.  
      2. Description of the Prior Art  
      Sounds are a fundamental way in which people communicate with others. Regardless, if it is voice or music, all are sent by sounds. As new technologies are developed progressively, sounds remain an important way for people to communicate or relax. Products such as audio systems are important products for people to enjoy music and relax. This is especially true of wireless audio systems. The most convenient way to transmit sounds is via air transmission. For instance, a wireless radio utilizes a wireless connection instead of a wired connection, and transmits and receives signals wirelessly. If a user wears a wireless headphone and stays within the wireless signal coverage, the user can hear audio through the wireless headphone. This makes it convenient for the user to move at will within the wireless signal coverage.  
      As stereo systems have developed, the user enjoys better surround effects. However, the surround effects of such a stereo coverage is limited due to the position of the user. If the user moves a little from the optimal reception area, the surround effects are enormously reduced. Therefore, manufacturers propose a system of 5.1 stereo channel to create better stereo surround effects. The system of 5.1 stereo channel has left/right channels, a center channel, left/right surround channels, and a low frequency effect channel. The system of 5.1 stereo channel includes digital theater system (DTS) and Dolby Digital 5.1, called audio code-3 (AC-3). The two systems are supported by Sony/Philips digital interface format (SPDIF), which is a standard interface for a digital audio system. Such a digital audio system can transmit signals formatted for Dolby or DTS and is also supported by DVD and home theater, transmitting 5.1 stereo channel signals through wired connections.  
      5.1 stereo channel includes six channels, two front channels, two rear channels, a center channel, and a low frequency effects channel and thereby six speakers, and six wires are needed to connect corresponding channels to an audio/video receiver (AVR), or to six analog output ports of a DVD player. Due to the complexity of the six connections, the user must make sure that the six connections are correct, or the entire multi-channel surround effects are disordered. The prior art wired headphone can achieve the multi-channel surround effect, but the connections are complex and the user is confined due to the length of wires.  
      In the prior art, some wireless headphones also provide the stereo surround effect and are more convenient than wired headphones. For example, U.S. Pat. No. 6,614,912 discloses an infrared-ray wireless headphone using two speakers to simulate the multi-channel effects. The principle is to transform multi-channel signals into left/right channel signals, and then wirelessly send the transformed signals to the headphone. However, the sound effect simulation using two speakers cannot perform perfect stereo surround effects. Furthermore, the transmission coverage of infrared-ray is small and infrared-rays cannot travel through objects. Hence, the user is confined to the room where the signal source is.  
      The following is transmission data rate for AC3 and DTS:  
      Dolby Digital (AC 3): 384˜448 kb/s  
      DTS: average ˜1500 kb/s  
      MPEG 2 Layer II: 640 kb/s  
      MPEG 2 AAC: 320 kb/s  
      As known in the prior art, the wireless transmission data rate for Bluetooth is 723 kb/s, not conforming (not fast enough) to all the above specifications. Analog transmissions (such as FM, AM) do not conform to SPDIF. Moreover, a specification of a signal delay time among each channel for AC3 is strict. For instance, the signal delay time between the rear channels and front channels depends on the distance from each speaker to the user, and should be within 10 ms. If the signal delay time does not conform to the specification, or the wireless transmission is not transmitted in real time, the Dolby multi-channel surround effects are not achieved.  
      Take WLAN for example. The wireless transmission data rate for WLAN conforms to the specifications. However, if the transmission is disturbed leading to errors in packets, the solution is to re-transmit the packets. The solution is feasible for general data but not audio signals. This would cause the stereo surround effect to be discontinuous. Take Bluetooth 1.1 for example, most signal delay time does not conform to AC3. From the above discussion, a digital wireless multi-channel audio system, equipped with a wireless transmitter of low signal delay time (less than 2 ms) and high transmission data rate (2000 kb/s), is needed to simultaneously send multi-channel signals to a wireless headphone having multiple speakers, such that the wireless headphone can provide the real multi-channel surround effects.  
     SUMMARY OF INVENTION  
      It is therefore a primary objective of the claimed invention to provide a wireless multi-channel audio system to solve the above-mentioned problems.  
      The claimed invention discloses a wireless multi-channel audio system. The system includes a receiving unit, a decoder, a sound channel mixing and processing unit, and a plurality of speakers. The receiving unit receives and demodulates a wireless audio signal. The decoder is electrically connected to the receiving unit and decodes the demodulated audio signal into a plurality of multi-channel signals. The sound channel mixing and processing unit mixes and processes the multi-channel signals to generate a plurality of mixing signals for different stereo effects. The plurality of speakers output sounds according to the mixing signals.  
      These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.  
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       FIG. 1  to  FIG. 6  are diagrams of a wireless multi-channel headphone system according to the present invention.  
       FIG. 7  is a diagram of a wireless multi-channel audio system according to the present invention.  
       FIG. 8  is a diagram of a wireless transmitter according to the present invention.  
       FIG. 9  is a diagram of a wireless receiver according to the present invention. 
    
    
     DETAILED DESCRIPTION  
      Please refer to  FIG. 1 , which is a diagram of an analog-output, wireless multi-channel headphone system  10 . The wireless multi-channel headphone system  10  includes a receiving unit  12 , a decoder  14 , a digital-to-analog converter (DAC)  16 , a sound channel mixing and processing unit  18 , an amplifier  22 , and a speaker  24 . The receiving unit  12  receives and demodulates a wireless signal having multi-channel signals or conforming to Sony/Philips digital interface format (SPDIF). After that, the decoder  14  decodes each channel signal and transmits each decoded signal to the DAC  16 . In the embodiment of  FIG. 1 , each decoded channel signal is mixed and processed in analog manner. The DAC  16  transforms the decoded digital signals into analog signals and then the analog signals are transmitted to the sound channel mixing and processing unit  18 . The signals processed by the sound channel mixing and processing unit  18  are inputted into the amplifier  22  to drive the speaker  24 . The speaker  24  outputs sounds according to the signals outputted from the amplifier  22 .  
      Please refer to  FIG. 2 , which is a diagram of an all-digital wireless multi-channel headphone system  20  according to the present invention. The wireless multi-channel headphone system  20  is a digital example of the present invention. The wireless multi-channel headphone system  20  comprises a receiving unit  12 , a decoder  14 , a digital signal processor (DSP)  26 , a pulse-width modulation (PWM) unit  28 , a digital amplifier  32 , and a speaker  24 . The function of the wireless multi-channel headphone system  20  of  FIG. 2  is similar to that of the wireless multi-channel headphone system  10  of  FIG. 1 . In  FIG. 1 , the digital signals are transformed into the analog signals after the multi-channel signals are decoded. After that, the signals are processed and amplified in analog manner. However, the signals of  FIG. 2  are all processed digitally. The receiving unit  12  receives and demodulates a wireless signal having multi-channel signals or conforming to SPDIF. The decoder  14  decodes each channel signal and outputs the signals to the DSP  26  to provide a variety of stereo effects. The PWM unit  28  and the digital amplifier  32  are used to amplify the signals to drive the speaker  24 . Finally, the speaker outputs Dolby surround sounds based on each channel signal.  
      Please refer to  FIG. 3 , which is a diagram of a wireless multi-channel headphone system  30  according to the present invention. The wireless multi-channel headphone system  30  comprises a receiving unit  12 , a decoder  14 , a sound channel mixing and processing unit  34 , an amplifier  37 , a headphone  36 , and four speakers  24 . The receiving unit  12  and the decoder  14  perform the same function mentioned above to decode six-channel audio signals for Dolby Digital effect. The six-channel audio signals are a left channel signal L 0 , a right channel signal R 0 , a center channel signal C 0 , a low frequency effect signal LFE 0 , a rear-left channel signal RL 0 , and a rear-right channel signal RR 0 . The sound channel mixing and processing unit  34  combines, composes, or mixes different channel signals in a digital or analog manner, and outputs such signals to the amplifier  37 . As shown in  FIG. 3 , the six-channel signals are transformed into a left channel signal L 32 , a right channel signal R 32 , and a low frequency effect signal LFE 32 . The signals L 32  and R 32  are derived from the five signals, L 0 , R 0 , C 0 , RL 0 , and RR 0 . The signal R 32  is amplified and transformed into the signal R 33  and then transmitted to the headphone  36  to drive a speaker  24  in the right side. The signal L 32  is amplified and transformed into the signal L 33  and then transmitted to the headphone  36  to drive a speaker  24  in the left side. The signal LFE 32  is amplified and transformed into the signal LFE 33  and then transmitted to the headphone  36  to drive two low frequency effect speakers  24  in the left and right side, respectively. After the user receives sounds outputted from the four speakers  24  according to different channel signals, the user can experience multi-channel surround effects.  
      Please refer to  FIG. 4 , which is a diagram of a wireless multi-channel headphone system  30  according to the present invention. The operation of the embodiment of  FIG. 4  is similar to that of the embodiment of  FIG. 3 . As shown in  FIG. 4 , the six-channel signals are combined and processed into four audio signals: a left channel signal L 42 , a right channel signal R 42 , a rear-left channel signal RL 42 , and a rear-right channel signal RR 42 . For instance, the signal L 42  is a mixture of the signals L 0  and C 0 . The signal R 42  comprises R 0  and C 0 . The signal RR 42  is derived from the mixture of RR 0  and LFE 0  while the signal RL 42  is derived from the mixture of RL 0  and LFE 0 . The signals L 42  and RL 42  are amplified and simultaneously transmitted to the headphone  36  to drive the speakers  24  in the left side. In the same way, the signals R 42  and RR 42  are amplified and simultaneously transmitted to the headphone  36  to drive the speakers  24  in the right side.  
      Please refer to  FIG. 5 , which is a diagram of another wireless multi-channel headphone system  30  according to the present invention. The embodiment of  FIG. 5  is similar to that of  FIG. 4 . The six-channel audio signals L 0 , R 0 , C 0 , LFE 0 , RL 0 , and RR 0 , outputted from the decoder  14  are transformed into the signals L 52  and RL 52  transmitted to the speakers  24  in the left side, the signals R 52  and RR 52  transmitted to the speakers  24  in the right side, and the low frequency effect signal LFE 52 . As shown in  FIG. 5 , the five signals are transmitted to the speakers  24  of the headphone  36  to provide stereo effects.  
      Please refer to  FIG. 6 , which is a diagram of a wireless multi-channel headphone system  30  according to the present invention. In this case, the six-channel audio signals L 0 , R 0 , C 0 , LFE 0 , RL 0 , and RR 0  outputted from the decoder  14  are not mixed. The sound channel mixing and processing unit  34  performs a digital-to-analog transformation or a digital signal process to produce the input signals of the amplifier  37  for stereo effects. There are four speakers  24  in each side of the headphone  36 . The four speakers  24  in the left side respectively output sounds based on the left channel signal, the rear-left channel signal, the center channel signal, and the low frequency effect signal. The four speakers  24  in the right side respectively output sounds based on the right channel signal, the rear-right channel signal, the center channel signal, and the low frequency effect signal.  
      Please refer to  FIG. 7 , which is a diagram of a wireless multi-channel audio system  100  according to the present invention. The audio system  100  comprises a multi-channel player  42 , such as a DVD player, a wireless transmitter  50 , a wireless receiver  80 , a decoder  14 , a sound channel mixing and processing unit  34 , an amplifier  22 , and a speaker  24 . The operations of the decoder  14 , the sound channel mixing and processing unit  34 , an amplifier  22 , and a speaker  24  are similar to those mentioned above. Due to a limitation of transmission data rate for audio code-3 (AC3) or digital theater system (DTS), and a rule of delay time for converting signals among each channel for AC3 specification, a conventional transmitter cannot transmit signals correctly and thereby the purposes of playing audio in real time and Dolby multi-channel effects are not achieved. The wireless transmitter  50  and the wireless receiver  80  of the present invention have properties of a low signal delay time (less than 2 ms) and a high transmission data rate (2000 kb/s) to modulate, transmit, receive, and demodulate a wireless signal formatted for SPDIF in real time. After a signal is transmitted from the player  42  to the wireless transmitter  50  through a cable, the wireless transmitter  50  transforms the signal into a wireless signal. The wireless receiver  80  simultaneously receives and demodulates the SPDIF signal sent by the wireless transmitter  50 , and then the signal is passed to the decoder  14  for other processes.  
      Please refer to  FIG. 8 , which is a diagram of the wireless transmitter  50 . The wireless transmitter  50  comprises a media access controller (MAC)  52  for audio and data, a modulation module  68 , and a radio frequency (RF) transmitting circuit  70 . The media access controller  52  includes a digital format converter  58 , a synthesizing module  60 , and an SPDIF connection  54 , such as an optical fiber connection or a coaxial cable connection. The media access controller  52  receives multi-channel input signals for different formats, such as AC3 or DTS. The digital format converter  58  electrically connected to the SPDIF connection  54  transforms the digital audio signal outputted from the SPDIF connection  54  into a pulse code modulation (PCM) signal. Finally, the synthesizing module  60  connected to the digital format converter  58  transforms a control signal and the PCM signal into a bit-stream signal. The modulation module  68  electrically connected to the synthesizing module  60  modulates the bit-stream signal to a corresponding base-band signal. The modulation module  68  includes a modulating circuit  67  and a spreading circuit  69 . The modulating circuit  67  can be a π/4-differential quadrature phase shift keying (DQPSK) circuit for modulating the bit-stream signal outputted from the synthesizing module  60  to generate a modulated signal. The spreading circuit  69  electrically connected to the modulating circuit  67  utilizes the modulated signal and a spread-spectrum code to perform a convolution multiplication. That is, every bit of the modulated signal is replaced with a plurality of bits to generate the base-band signal. The base-band signal is transformed into an RF signal with high frequency by the RF transmitting circuit  70  and then wirelessly transmitted through the air.  
      Please refer to  FIG. 9 , which is a diagram of the wireless receiver  80 . The wireless receiver  80  comprises a media access controller (MAC)  82  for audio and data, a demodulation module  94 , and a radio frequency (RF) receiving circuit  92 . The media access controller  82  includes a separating module  84  and a digital format converter  88 . The separating module  84  separates the bit-stream signal into a control signal and a PCM signal. The digital format converter  88  electrically connected to the separating module  84  transforms the PCM signal into a digital audio signal. The format of the digital signal outputted from the media access controller  82  conforms to SPDIF or I2S format. The media access controller  82  of the present invention also outputs a control signal to control the audio signal, as shown in  FIG. 9 .  
      The RF receiving circuit  92  receives an RF signal and generates a corresponding base-band signal. The demodulation module  94  electrically connected to the RF receiving circuit  92  performs an anti-operation of the modulation module  68 ; that is, the demodulation module  94  demodulates the base-band signal into the bit-stream signal of  FIG. 8 . How the demodulation module  94  demodulates signals is described as follows. The demodulation module  94  includes a de-spreading circuit  93  and a demodulating circuit  95 . The de-spreading circuit  93  utilizes the base-band signal and a spread-spectrum code to perform a convolution multiplication to transform the base-band signal into a de-spreading signal. The demodulating circuit  95  demodulates the de-spreading signal in π/4-DQPSK manner to generate the bit-stream signal. Finally, the wireless receiver  80  sends the SPDIF signal to the decoder  14  of  FIG. 7 .  
      In the prior art, signals are transmitted to a multi-channel headphone through cables. Although the prior art can transmit SPDIF signals conforming to the multi-channel specification, the connection is complicated. This makes it inconvenient for the user to move around due to the length of cables. However, the present invention provides the user with the convenience of a wireless headphone. Another prior art of infrared-ray wireless headphone communicates the headphone with the player wirelessly. However, the transmission distance is very short and the infrared-ray cannot travel through objects. In addition, the infrared-ray wireless headphone utilizes two speakers to simulate multi-channel effects far from the real multi-channel effects. Moreover, Bluetooth transmission or analog transmission (such as FM, AM) cannot completely support SPDIF format. Although the wireless transmission data rate of WLAN is very high, it cannot transmit a complete SPDIF signal to the headphone having multiple speakers in real time and thereby the real multi-channel effect is not achieved. Compared with the prior art, the wireless multi-channel audio system of the present invention is capable of simultaneously transmitting and receiving signals formatted for SPDIF. The decoder and the sound channel mixing and processing unit of the present invention send SPDIF signals to the wireless headphone having multiple speakers wirelessly. Therefore, the wireless headphone of the present invention can achieve real multi-channel effects with high-end and high quality for AC3 or DTS.  
      Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.