Patent Publication Number: US-9424855-B2

Title: Audio device and method for adding watermark data to audio signals

Description:
BACKGROUND 
     1. Technical Field 
     The disclosure relates to audio devices, and particularly to a method for an audio device to add watermark data to audio signals. 
     2. Description of Related Art 
     With the development and comprehensive use of multimedia and digital communications, authenticity and protection of the multimedia such as, audio and video and the security of information is getting more important. Ordinarily, when making an audio disc, for example, the original audio signal is output just after being converted from analog to digital, therefore it is easy to divulge information of the original audio signal and difficult to find out a source of the divulgement. Thus, copyright laws can be broken resulting in loss in commerce. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the present embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present embodiments. Moreover, in the drawings, all the views are schematic, and like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a schematic diagram of one embodiment of an audio device as disclosed. 
         FIG. 2  is a schematic diagram of another embodiment of an audio device as disclosed. 
         FIG. 3  is a circuit diagram of one embodiment of the audio device as disclosed. 
         FIG. 4  is a circuit diagram of one embodiment of the audio device as disclosed. 
         FIG. 5  is a flowchart of one embodiment of a watermark data of an audio signals adding method. 
         FIG. 6  is a simulation waveform of the watermark data, a high frequency noise signal, a first added data and a second added data as disclosed. 
         FIG. 7  is a simulation waveform of an original audio signal and an output audio signal as disclosed. 
     
    
    
     DETAILED DESCRIPTION 
     The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean “at least one.” 
       FIG. 1  is a schematic diagram of one embodiment of an audio device  10  as disclosed. In one embodiment, the audio device  10 , a set-top box, for example, generates or records audio signals, and adds a watermark data to the audio signals. The watermark data can be used to find out a source of a leak of the audio signals through reverse extraction of the added watermark data. 
     The audio device  10  comprises a processor  100 , an audio processing module  180 , a high frequency noise generating circuit  110 , a first switch control circuit  140 , a second switch control circuit  150 , a low pass filter circuit  160 , and an adder circuit  170 . The processor  100  controls operation of the audio device  10  and generates the watermark data. In one embodiment, the watermark data comprises digital signals comprising high level logic digital signals  1  and low level logic digital signals  0 . The watermark data includes digital copyright information, such as hardware serial numbers of the audio device  10 , which can be used to find out the source of the leak of the audio signals. The watermark data includes the header information, the digital right information, and last information. For example, when the watermark data comprises 10101010 1111010000101001 01010101, then “10101010” is the header information, “1111010000101001” is the digital right information, and “01010101” is the last information. The audio processing module  180  connects to the processor and generates an original audio signal. The high frequency noise generating circuit  110  generates a high frequency noise signal. In one embodiment, frequency band of the high frequency noise signal which is generated by the high frequency noise generating circuit  110  is above 20 KHz, and the high frequency noise signal generated by the high frequency noise generating circuit  110  will not influence the original audio signal because 20 KHz is beyond scope of human hearing. 
     The first switch control circuit  140  is connected to the processor  100  and the second switch control circuit  150  is connected to the high frequency noise generating circuit  110 , the high frequency noise signal passes through the first switch control circuit  140  and the second switch control circuit  150  according to a different voltage level of the watermark data, the high frequency noise signal passes through the corresponding switch of the first switch control circuit  140  and the second switch control circuit  150 . In one embodiment, the high frequency noise signal passes through the first switch control circuit  140  when the watermark data is the high level logic signals  1 . The high frequency noise signal passes through the second switch control circuit  150  when the watermark data is the low level logic signals  0 . Thus, the high frequency noise signal will not simultaneously pass through both the first switch control circuit  140  and the second switch control circuit  150 , but only pass through one of the first switch control circuit  140  and the second switch control circuit  150 . In another embodiment, the first switch control circuit  140  controls the high frequency noise signal to pass through the first switch control circuit  140  when the watermark data is the low level logic signals  0 , and the second switch control circuit  150  controls the high frequency noise signal to pass through the second switch control circuit  150  when the watermark data is the high level logic signals  1 . 
     The low pass filter circuit  160  is connected to the first switch control circuit  140 , the low pass filter circuit  160  comprises at least a low pass filter unit  161 , referring to  FIG. 3  and  FIG. 4 , and the low pass filter unit  161  filter the high frequency noise signal received from the first switch control circuit  140  to form a first added data. In one embodiment, compared to the high frequency noise signal, a voltage amplitude of the first added data is less than a voltage amplitude of the high frequency noise signal because the first added data is the high frequency noise signal that was filtered. In one embodiment, the high frequency noise signal that is output by the second switch control circuit  150  forms a second added data. 
     The adder circuit  170  receives the first added data from the low pass filter circuit  160 , the second added data from the second switch control circuit  150 , and the original audio signal from the audio processing module  180 . The adder circuit  170  adds the first added data and the second added data to the original audio signal to output an output audio signal to other devices or play. 
       FIG. 6  is a simulation waveform of the watermark data, the high frequency noise signal, the first added data, and the second added data as disclosed. In one embodiment, the watermark data is approximately a square wave with alternating high and low potential. The first added data corresponds to the high voltage level of the watermark data and is the high frequency noise signals that have been filtered by the low pass filter circuit  160 . Thus, the voltage amplitude of the first added data is less than that of the high frequency noise signal. The second added data corresponds to the low voltage level of the watermark data and is original high frequency signals. That is, the audio device  10  uses high frequency noise signal with different voltage levels as the watermark data to superpose to the original audio signal. From this point on, the high frequency noise signal will be called a carrier signal. The high frequency noise signal that is added to the original audio signal will not influence the original audio signal because frequency band of the high frequency noise signal is above 20 KHz, accordingly, quality of the original audio is assured. 
       FIG. 2  is a schematic diagram of another embodiment of an audio device  20  as disclosed. In one embodiment, difference between the audio device  20  and the audio device  10  in  FIG. 2  is that the audio device  20  further comprises a first voltage follower  120  and a second voltage follower  130  and the low pass filter circuit  160  is further connected to the processor  100  to receive the watermark data. The first voltage follower  120  is connected between the high frequency noise generating circuit  110  and the first switch control circuit  150 . Thereby, the signal generated by the first switch control circuit  140  and the second switch control circuit  150  will not return to the high frequency noise generating circuit  110 , which avoids affecting the original high frequency noise signal. 
       FIG. 3  is a circuit diagram of one embodiment of the audio device  10 . In one embodiment, the first switch control circuit  140  comprises a first switch unit Q 1  and a second switch unit Q 2 . The first switch unit Q 1  and the second switch unit Q 2  both comprise a control end, a first electrode, and a second electrode. The control end of the first switch unit Q 1  is connected to a reference voltage through a first resistor R 1 . The first electrode of the first switch unit Q 1  is connected to the low pass filter circuit  160  and the high frequency noise generating circuit  110  to receive the high frequency noise signal. The second electrode of the first switch unit Q 1  is grounded. The control end of the second switch unit Q 2  receives the watermark data from the processor  100  through a second resistor R 2 . The first electrode of the second switch unit Q 2  is connected to the control end of the first switch unit Q 1  and the second electrode of the second switch unit Q 2  is grounded. In one embodiment, the first switch unit Q 1  may be a N-type Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET). The control end of the first switch unit Q 1  may be a gate of the NMOS, the first electrode of the first switch unit Q 1  may be a drain of the NMOS, and the second electrode of the first switch unit Q 1  may be a source of the NMOS. The second switch unit Q 2  may be a npn bipolar transistor. The control end of the second switch unit Q 2  may be a base of the npn bipolar transistor. The first electrode of the second switch unit Q 2  may be a collector of the npn bipolar transistor, and the second electrode of the second switch unit Q 2  may be an emitter of the npn bipolar transistor. 
     The second switch control circuit  150  comprises a third switch unit Q 3  comprising a control end, a first electrode, and a second electrode. The control end of the third switch unit Q 3  is connected to the processor  100  that receives the watermark data. The first electrode of the third switch unit Q 3  connected to the adding circuit  170  and the high frequency noise generating circuit  110  and the second electrode of the third switch unit Q 3  are connected to ground. In one embodiment, the third switch unit Q 3  may be an NMOS. The control end of the third switch unit Q 3  may be a gate of the NMOS. The first electrode of the third switch unit Q 3  may be a drain of the NMOS, and the second electrode of the third switch unit Q 3  may be a source of the NMOS. 
     The low pass filter circuit  160  comprises a low pass filter unit  161 . In one embodiment, the low pass filter unit  161  comprises a third resistor R 3 , a fourth resistor R 4 , a fifth resistor R 5 , a sixth resistor R 6 , a first capacitor C 1 , a second capacitor C 2 , a third capacitor C 3 , and a first comparator  1600 . A first end of the third resistor R 3  is connected to the first electrode of the first switch unit Q 1  of the first switch control circuit  140  to receive the high frequency noise signal, and a second end of the third resistor R 3  is grounded through the first capacitor C 1 . A first end of the fourth resistor R 4  is connected to the second end of the third resistor R 3 , and a second end of the fourth resistor R 4  is grounded through the second capacitor C 2 . The first comparator  1600  having a positive input end connected to ground, a negative input end connected to the second end of the fourth resistor R 4  through the fifth resistor R 5 . In addition, an output end that is connected to the second end of the fourth resistor R 4  through the third capacitor C 3  and the second end of the third resistor R 3  through the sixth resistor R 6  outputs the first added data. 
     The adder circuit  170  comprises an inverting adder  1700 . A negative input end of the inverting adder  1700  is connected to the first electrode of the third switch unit Q 3  of the second switch control circuit  150  through a seventh resistor R 7 , the output end of the first comparator  1600  through a eighth resistor R 8 , and receives the original audio signal from the audio processing module  180 . An output end of the inverting adder  1700  outputs the audio signals. In one embodiment, a positive input of the inverting adder  1700  is grounded, and the output end of the inverting adder  1700  is connected to the negative input of the inverting adder  1700  through a ninth resistor R 9 . 
     At a first moment, such as the time 0-12 ms in  FIG. 6 , when the watermark data is the high level logic signals, the second switch unit Q 2  of the first switch control circuit  140  is switched, an electric potential of the control end of the first switch unit Q 1  decreases, the first switch unit Q 1  turns off. Thereby, the high frequency noise signal is output to the low pass filter circuit  160  by the high frequency noise generating circuit  110 . The low pass filter circuit  160  filters the high frequency noise signal to form the first added data whose voltage amplitude decreases. In addition, transmits the first added data to the adder circuit  170  through the eighth resistor R 8 . All together, the third switch unit Q 3  of the second switch control circuit  150  is switched, an electric potential of the first electrode of the third switch unit Q 3  decreases, and the carrier signal cannot enter the adder circuit  170 . At that moment, the added data only is the first added data, and the adder circuit  170  adds the first added data to the original audio signal. 
     Next, at such a time as 12-25 ms as shown in  FIG. 6 , when the watermark data is the matching low logic signal, the second switch unit Q 2  turns off. The first switch unit Q 1  is switched, the electric potential of the first electrode of the first switch unit Q 1  decreases, and the carrier signal cannot enter the low pass filter circuit  160 . The low pass filter circuit  160  has no output data for the adder circuit  170 . Simultaneously, the third switch unit Q 3  of the second switch control circuit  150  turns off, the high frequency noise signal is transmitted to the adder circuit  170  through high frequency noise generating circuit  110 . At that moment, the added data only is the second added data. The adder circuit  170  adds the second added data to the original audio signal. In this analogy, the audio device  10  generates the different voltage levels of the high frequency noise signals as the watermark data to superpose to the original audio signal. The quality of the output audio signal is assured.  FIG. 7  is a simulation waveform of the original audio signal and the output audio signal. It can be seen from the figure that the waveform of the original audio signal and the output audio signal are almost the same, it indicates that the high frequency noise signal that is added to the original audio signal will not influence the original audio signal, the quality of the output audio signal is assured. 
       FIG. 4  is a circuit diagram of one embodiment of the audio device  20 . In one embodiment, differences between the audio device  20  and the audio device  10  in  FIG. 3  are the circuit of the first voltage follower  120 , the second voltage follower  130 , and the low pass filter circuit  160 . The first voltage follower  120  is connected between the high frequency noise generating circuit  110  and the first electrode of the first switch unit Q 1  of the first switch control circuit  140 . The first voltage follower  120  is connected between the high frequency noise generating circuit  110  and the first electrode of the first switch unit Q 1  of the first switch control circuit  140 . The second voltage follower  130  is connected between the high frequency noise generating circuit  110  and the first electrode of the third switch unit Q 3  of the second switch control circuit  150 . 
     In one embodiment, the low pass filter circuit  160  comprises two low pass filter units  161  which are connected in series between the first switch control circuit  140  and the adder circuit  170 . The low pass filter circuit  160  further comprises a fourth switch unit Q 4  and a fifth switch unit Q 5 . The fourth switch unit Q 4  and the fifth switch unit Q 5  both comprise a control end, a first electrode, and a second electrode. The control end of the fourth switch unit Q 4  is connected to a reference voltage through a tenth resistor R 10 . The first electrode of the fourth switch unit Q 4  is connected to the output end of the low pass filter circuit  160 , which is the output end of the first comparator  1600  of the another low pass filter unit  161 . The second electrode of the fourth switch unit Q 4  connected to ground. The control end of the fifth switch unit Q 5  receives the watermark data through an eleventh resistor R 11 . The first electrode of the fifth switch unit Q 5  connected to the control end of the fourth switch unit Q 4 , and the second electrode of the fifth switch unit Q 5  is connected to ground. 
     In one embodiment, the fourth switch unit Q 4  may be an NMOS. The control end of the fourth switch unit Q 4  may be a gate of the NMOS. The first electrode of the fourth switch unit Q 4  may be a drain of the NMOS, and the second electrode of the fourth switch unit Q 4  may be the source of the NMOS. The fifth switch unit Q 5  may be a npn bipolar transistor. The control end of the fifth switch unit Q 5  may be a base of the npn bipolar transistor. The first electrode of the fifth switch unit Q 5  may be a collector of the npn bipolar transistor, and the second electrode of the fifth switch unit Q 5  may be a the emitter of the npn bipolar transistor. 
     At first such as the time 0-12 ms as shown in  FIG. 6 , when the watermark data is the high level logic signals. The second switch unit Q 2  of the first switch control circuit  140  is switched, an electric potential of the control end of the first switch unit Q 1  decreases, and accordingly the first switch unit Q 1  turns off. Thereby, the high frequency noise signal is output to the low pass filter circuit  160  by the high frequency noise generating circuit  110 . The low pass filter circuit  160  filters the high frequency noise signal by the two low pass filter units  161  to form the first added data whose voltage amplitude decreases. At that moment, the fifth switch unit Q 5  of the low pass filter circuit  160  is switched, an electric potential of the control end of the fourth switch unit Q 4  decreases, and the fourth switch unit Q 4  is turned off. Thereby, the first added data is transmitted to the adder circuit  170  through the eighth resistor R 8 . Simultaneously, the third switch unit Q 3  of the second switch control circuit  150  is switched, electric potential of the first electrode of the third switch unit Q 3  decreases, and the carrier signal cannot enter to the adder circuit  170 . The added data is the first added data, the adder circuit  170  adds the first added data to the original audio signal. 
     Next, at such a time as 12-25 ms in  FIG. 6 , when the watermark data is the matching low logic signal, the second switch unit Q 2  turns off, the first switch unit Q 1  is switched, the electric potential of the first electrode of the first switch unit Q 1  decreases, and accordingly the high frequency noise signal cannot enter to the low pass filter circuit  160 . At that moment, the fifth switch unit Q 5  of the low pass filter circuit  160  turns off, the fourth switch unit Q 4  is switched. In addition, the potential of the output end of the low pass filter circuit  160  decreases, assuring that the low pass filter circuit  160  has no data to output. Further, the added data superposed by the adder circuit  170  is completely corresponding to the watermark data. Thereby, the low pass filter circuit  160  has no output data for the adder circuit  170 . Simultaneously, the third switch unit Q 3  of the second switch control circuit  150  turns off, the high frequency noise signal is transmitted to the adder circuit  170  through high frequency noise generating circuit  110 . At this moment, the added data only is the second added data, the adder circuit  170  adds the second added data to the original audio signal. In this analogy, the audio device  10  generates the different voltage levels of the high frequency noise signal as the watermark data to superpose to the original audio signal, assuring the quality of the output audio signal. 
       FIG. 5  is a flowchart of one embodiment of the watermark data of the audio signals adding method. The flowchart is executed by the modules of the audio device  10  of  FIG. 1 . Depending on the embodiment, additional blocks may be added, others deleted, and the ordering of blocks may be changed while remaining well within the scope of the disclosure. 
     In block S 500 , the audio processing module  180  generates the original audio signal, the processor  100  generates the watermark data, and the high frequency noise generating circuit  110  generates the high frequency noise signal. In the embodiment, frequency band of the high frequency noise signal is above 20 KHz, the watermark data is the signal that comprises the high level logic digital signal and the low level logic digital signal. Into block S 500 , the high frequency noise signal pass through the first switch control circuit  140  and the second switch control circuit  150  according to the different voltage levels of the watermark data. In the embodiment, the first switch control circuit  140  controls the high frequency noise signal to pass through the first switch control circuit  140  when the watermark data is the high level logic signals, the high frequency noise signal enter to the low pass filter circuit  160 . The second switch control circuit  150  controls the high frequency noise signal to pass through the second switch control circuit  150  when the watermark data is the low level logic signals, the high frequency noise signal enter to the adder circuit  170 . 
     In block S 520 , when the first switch control circuit  140  controls the high frequency noise signal to pass through the first switch control circuit  140  and the second switch control circuit  150  controls the high frequency noise signal to be blocked, the low pass filter circuit  160  filter the high frequency noise signal received to form the first added data. The first added data is the high frequency noise signals that have been filtered by the low pass filter circuit  160 , and voltage amplitude of the first added data decreases to replace the high potential watermark data. 
     Into block S 530 , when the first switch control circuit  140  controls the high frequency noise signal to be blocked and the second switch control circuit  150  control the high frequency noise signal to pass through the second switch control circuit  150 , the first switch control circuit  150  transmit the high frequency noise signal to the adding circuit  170  as second added data. In one embodiment, the second added data is the original audio signal, correspond to the low potential watermark data. 
     Into the block S 540 , the adding circuit  170  adds the first added data and the second added data into the original audio signal to make output audio signal. 
     The audio device  10  and the audio device  20  and the method for adding watermark data to audio signals in the present disclosure converts the watermark data of the high level logic signals and low level logic signals to different voltage levels of the high frequency noise signal, and add it to the original audio signal, which can find out the source of the leak through reverse extracting of the added watermark data when the divulgement happened, accordingly, quality of the original audio is assured. Moreover, the watermark data is converted to the high frequency noise signal and will not influence the original audio signal, accordingly, quality of the output audio signal is assured. 
     The foregoing disclosure of the various embodiments has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the present disclosure to the precise forms disclosed. Many variations and modifications of the embodiments described herein will be apparent to one of ordinary skill in the art in the light of the above disclosure. The scope of the present disclosure is to be defined only by the claims appended hereto and their equivalents.