Abstract:
The invention provides a multiple audio output system comprising a second input buffer storing a second data stream output from a demodulation unit or a demultiplexing unit, a second processing unit receiving and processing the second data stream to output a third data stream, a data buffer receiving a third data stream from the second processing unit, a multiplexer having input terminals receiving a first audio signal and the third data stream, and an output terminal outputting an output data stream, and a first processing unit receiving and processing the output data stream to output a first output signal to drive a first output device. The second processing unit further comprises a second decoder receiving and decoding the second data stream, and a second post processing unit receiving and processing the decoded second data stream to output a second output signal to drive a second output device.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an audio output system, and more particularly to a multiple output audio system capable of simultaneously playing or switching between different audio sources. 
     2. Description of the Related Art 
       FIG. 1  is a schematic block diagram of a dual program audio apparatus in accordance with U.S. Pat. No. 5,910,996. The System  30  intends to receive multiple sources from its input jacks  32   a  through  32   e , and output two of the sources by jacks  33   a  and  33   b . One of the outputs is used as foreground sound which is intended to attract the attention of the listeners, for example, news broadcasting. The other output is used as background sound such as background music which may draw less concentration from the listeners. Dual program amplifier circuit  31  receives as its input signals at input jacks  32   a - 32   e  first and second audio programs from a radio tuner A  34 , radio tuner B  35 , cassette tape player  36 , or a compact disc player  37 . In an automotive environment car telephone  38  may also be coupled to an input jack  32   e.    
     Dual program amplifier circuit  31  is coupled to audio speaker sets  39  and  40  via output jacks  33   a  and  33   b , respectively, and comprises switching circuit  41 , amplifier A  42  and amplifier B  43 . The volume of the audio program output by amplifier A  42  is controlled by volume select circuit  44 , while the volume of the audio program output by amplifier B  43  is controlled by volume select circuit  45 . 
     Switching circuit  41  receives and directs the input audio signals via input jacks  32   a - 32   e  to amplifier A  42  or amplifier B  43  to drive the audio speaker sets  39  or  40 . Although the dual output devices can be driven by the dual program amplifier circuit  31  is easily implemented, the decoding, demodulation or the demultiplexing operation for the input sources  34 - 38  are independent. The system  30  uses multiple source processors and directs to different output with a multiplexer. Thus, extensive hardware or software resources are required. A multiple output driving system capable of reducing the hardware or software resource loading and having adaptive processing paths is desirable. 
     BRIEF SUMMARY OF THE INVENTION 
     A multiple audio output system comprises a second buffer storing a second data stream output from a demodulation unit or a demultiplexing unit, a second processing unit receiving and processing the second data stream to output a third data stream, a data buffer receiving a third data stream from the second processing unit, a multiplexer having input terminals receiving a first audio signal and the third data stream, and an output terminal outputting an output data stream, and a first processing unit receiving and processing the output data stream to output a first output signal to drive a first output device. The second processing unit further comprises a second decoder receiving and decoding the second data stream, and a second post processing unit receiving and processing the decoded second data to output a second output signal to drive a second output device. 
     A controlling method for a multiple audio output system is also provided, wherein the multiple audio output system comprises a first processing unit receiving and processing a first signal and a second processing unit. The controlling method comprises stopping the first processing unit, fading out an output signal of the first processing unit, switching the input of the second processing unit from the first signal to a third signal, starting processing the third signal by the first processing unit, and fading in the output signal of the first processing unit. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  is an illustrative schematic block diagram of an illustrative dual program audio apparatus constructed in accordance with U.S. Pat. No. 5,910,996. 
         FIG. 2  is a block diagram illustrating an embodiment of a dual output audio system. 
         FIG. 3  is a block diagram illustrating another embodiment of the dual output audio system. 
         FIG. 4  is a flowchart illustrating one embodiment of the control method of the dual output audio system in  FIG. 2 . 
         FIG. 5  is a flowchart illustrating one embodiment of the control method of the dual output audio system in  FIG. 3 . 
         FIG. 6  is a flowchart showing TV channel switching for the dual audio output system in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
       FIG. 2  is a block diagram of an embodiment of the dual output audio system. The dual output audio system is a NPTV or DTV system, where the auxiliary output (second output) is always an NPTV/DTV audio signal while the main output (first output) is switchable between line-in or NPTV/DTV audio signal. The dual output audio system comprises a first input buffer  11 , a multiplexer  12 , a first processing unit  13 , a data buffer  14 , a demodulation/demultiplexing unit  15 , a second input buffer  16 , a second processing unit  17  and a selection unit  18 . The first input buffer  11  couples the first audio source to the multiplexer  12 . Some embodiments of the first audio source comprise a set-top box, a DVD player, or AV receiver. The first audio source provides digital audio data to the first input buffer  11  via a digital interface such as High-Definition Multimedia Interface (HDMI) and Inter-IC Sound (I 2 S). The multiplexer  12  receives data from the first input buffer  11  and the data buffer  14  and outputs one of the two data streams to the first processing unit  13  in accordance with a control signal (not shown in  FIG. 2 ). The first processing unit  13  receives and processes the data stream from the multiplexer  12  to generate a first audio signal to drive a first output device, such as a speaker or a headphone. In one embodiment, the first processing unit  13  comprises a first decoder  131 , a first post processing unit  132  and a first output buffer  133 . In another embodiment, the first processing unit  13  comprises only the first post processing unit  132 . The first decoder  131  decodes the data stream from the multiplexer  12 . The first post processing unit  132  processes the decoded signal, for example, of the first post processing unit  132  conducts the one or more of the following procedures, surrounding effect processing, volume controlling, echo, trim, bass, equalizing, decoding for time shift function, fade-in/fade-out, encryption or decryption, sampling rate conversion, and channel delay. The first output buffer  133  receives and buffers the first audio signal to drive the first output device. 
     The demodulation/demultiplexing unit  15  receives a signal from a second audio source. If the second audio source provides an NTSC analog TV audio signal, the demodulation/demultiplexing unit  15  demodulates the analog TV audio signal to the NTSC baseband. If the second audio source provides a digital TV audio signal, the demodulation/demultiplexing unit  15  demultiplexes the digital TV audio signal to acquire audio data corresponding to the selected channel. The second processing unit  17  generate a second audio signal to drive the second output device by receiving audio data from the second input buffer  16 . In one embodiment, the second processing unit  17  comprises a second decoder  171 , a second post processing unit  172  and a second output buffer  173 . The second decoder  171  decodes the audio data from the second input buffer. The second post processing unit  172  processes the decoded signal. This processing unit  172  may be similar to the processing unit  132  which performs audio processing such as surround effect processing, volume controlling, sampling rate conversion, or equalizing. The second output buffer  173  buffers the second audio signal to drive the second output device. The selection unit  18  receives and transmits a third data stream from the second processing unit  17  to the data buffer  14 , wherein the third data may be the output of the second decoder  171  or the second post processing unit  172 . The data buffer may be a dynamic random access memory (DRAM), static random access memory (SRAM), flash ram, pulse code modulated (PCM) buffer, hard disc or other storage medium. The selection unit  18  has two processing paths controlled by switch SW 1 , wherein one processing path directly passes through the third data stream to the data buffer  14 , and another processing path transmits the third data stream through the processing unit  19  to the data buffer  14 . The processing unit  19  can be changed based on the requirement of the first output device or the first processing unit  13 . For example, the processing unit  19  can be an encryption unit or an encoder for encrypting or encoding the third data stream. A corresponding decrypting unit or a corresponding decoder is sometimes desirable. Preferably, the corresponding decrypting unit or decoder is coupled between the first decoder  131  and the data buffer  14  when the multiplexer  12  selects the data buffer  14  as data sources. 
     In one embodiment, the first output device and the second output device are television receiving a TV signal and broadcast the same program, thus, according to the structure of  FIG. 2 , only the second processing unit need to process the TV signal, and the first processing is a re-producing unit directly transmitting the processed TV signal from the second processing unit to the first output device. 
       FIG. 3  is a block diagram illustrating another embodiment of the dual output audio system. The line-in buffer  21  buffers and transmits audio signal in audio-visual (A/V) source to the first multiplexer  24 . The demodulation unit  22  demodulates and transmits audio signal in TV source to the first multiplexer  24  and the second multiplexer  25 . The demultiplexing unit  23  demultiplexes and transmits audio signal in digital TV (DTV) source to the first multiplexer  24  and the second multiplexer  25 . The second processing unit  28  selects the TV source or the DTV source to process by the second decoder  281 . In one embodiment, the second processing unit  28  comprises a second decoder  281 , a second post processing unit  282 , and a second output buffer  283 . The second decoder  281  receives and decodes the data from the second multiplexer  25 . The second post processing unit  282  processes the decoded signal from the second decoder  281  by one or more at least one of procedures such as surrounding effect processing, volume controlling, echo, trim, bass, equalizing, time shifting, fade-in/fade-out, channel delay, sampling rate conversion, or any combination of the above. The second output buffer  283  receives and buffers the second audio signal to drive the second output device. The first multiplexer  24  receives signals from the line-in buffer  21 , demodulation unit  22 , demultiplexing unit  23 , and data buffer  27  and directs one of them to the first processing unit  26 . In one embodiment, the first processing unit  26  comprises a first decoder  261 , a first post processing unit  262  and a first output buffer  263 . In another embodiment, the first processing unit  26  comprises only the first post processing unit  262 . The first decoder  261  decodes and transmits the data from the first multiplexer  24  to the first post processing unit  262 . The first post processing unit  262  processes the decoded signal from the first decoder  261  by one or more at least one of procedures such as, surrounding effect processing, volume controlling, echo, trim, bass, equalizing, time shifting, fade-in/fade-out, and channel delay, sampling rate conversion, or any combination of the above. The first output buffer  263  receives and buffers the first audio signal to drive the first output device. 
     The selection unit  29  receives and transmits a third data stream from the second processing unit  28  to the data buffer  27 , wherein the third data stream may be generated by and output from the second decoder  281  or the second post processing unit  282 . The data buffer may be a dynamic random access memory (DRAM), static random access memory (SRAM), flash ram, pulse code modulated buffer (PCM buffer), hard disc or any kind of storage medium. The selection unit  29  having two processing paths controlled by the switch SW 1  is similar to the selection unit  18  in  FIG. 2 , so relevant descriptions are omitted. 
     By the first multiplexer  24  and the second multiplexer  25 , the first output device and the second output device can be driven by the same input source or different input sources. For example, if both the first and second output devices play the TV signal, the first multiplexer  24  and the second multiplexer  25  may respectively direct the signal from the demodulation unit  22  to the first processing unit  26  and the second processing unit  28 . In one application, the first output device plays the TV signal by the operating of the data buffer  27  and the second processing unit  28 . 
     In some embodiments, the first output device is a television speaker and the second output device is a DVD recorder, the television can receive a TV signal from the demodulation unit  22  or the data buffer  27 . In this case, the TV signal is from the data buffer  27 . The data buffer  27  receives a processed TV signal from the second decoder  281  or the second post-processing unit  282  through the selection unit  29 . If the audio signals required by the television and DVD recorder are the same, such as a 2 channel audio signal, the data buffer  27  receives a TV signal from the second post-processing unit  282 , and the first processing unit can bypass it to the television. In some embodiments, the audio required by the DVD recorder is a 2 channel audio signal and the audio required by the TV is a 5 channel audio signal, the 2 channel audio signal will be converted to 5 channel audio signal by the processing  291  or the first post-processing unit  262  before transmitting to the television. In some embodiments, the output signal of the second processing unit is output via a scart connector. 
       FIG. 4  is a flowchart showing an exemplary embodiment of the control method, switching line-in mode to TV mode to prevent pop noise, of the dual output audio system in  FIG. 2 . The first processing unit  13  is first in a line-in mode, i.e. the first processing unit  13  processes a line-in signal, such as an AV signal from the first input buffer  11 . The second processing unit  17  processes a TV signal.  FIG. 4  shows switching the first processing unit  13  from the line-in mode to a TV mode. In step S 41 , the first decoder  131  stops and the output signal of the first processing unit  13  is faded out (step S 42 ). In step S 43 , the first processing unit  13  changes the input source by switching the output of the multiplexer  12  from the AV signal to a TV signal. In this case, the multiplexer  12  directs the signal from the data buffer  14  to the first processing unit  13 . In step S 44 , the first decoder  131  plays in the TV mode, and the output signal of the first processing unit  13  is faded in (step S 45 ). 
       FIG. 5  is a flowchart showing an embodiment of the control method of the dual output audio system in  FIG. 3 . The operation illustrated in  FIG. 5  is a mode switching operation for the first output device changing from a line-in mode to DTV mode. The second processing unit  28  initially processes the DTV signal and provides a third data stream to the first processing unit  26  via the data buffer  27  and the selection unit  29 . Assuming the first processing unit  26  is initially processing the AV source (line-in mode), the first output device is a television, and the second output device is a DVD recorder which initially records the DTV program. When the television changes its audio source from the AV signal to the DTV signal, a mode switching procedure is executed as show in  FIG. 5 . In steps S 51  and S 52 , the first decoder  261  stops processing the AV signal and the output signal of the first processing unit  26  is faded out. In step S 53 , the first multiplexer directs the audio signal from the data buffer  27  to the first processing unit  26 , thus, the television changes from the line-in mode to the DTV mode. In steps S 54  and S 55 , the first processing unit  26  is played and faded in, and first output device is changed to DTV mode. In the embodiment, the third data stream comprises decoded DTV signals which can be directly broadcasts by the television, so the first decoder does not need to decode the DTV signal and the software resource can be reduced. Furthermore, in the embodiment, the first processing unit  26  does not comprise the first decoder  261  when the first output device and the second output device process the same audio signal. 
       FIG. 6  is a flowchart showing TV channel switching for the dual audio output system in  FIG. 2 . In this embodiment, the main processing unit is the second processing unit  17  and the first processing unit  13  is re-producing unit for directly transmitting the audio data from the second processing unit  17  to the first output device. When the second output device, a television, changes TV channel, a channel switching procedure is executed as shown in  FIG. 6 . In step S 61 , the second decoder 171  fades out and the demodulation unit/demultiplexing unit  15  then strikes another frequency for changing TV channel in step S 62 . After switching TV channel, the second decoder  171  fades in (Step S 63 ). In this embodiment, the first output device operates based on the output signal from the second processing unit  17 , in other words, when the second decoder  171  fades out, the first output devices fades out, and when the second decoder  171  fades in, the first output device fades in. In the embodiment, the first output device is a DVD recorder for recording the TV program showing on the television, the first output device, and when the television changes TV channel, the TV program recorded by the DVD recorder also changes. 
     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.