Audio Distribution System

Abstract

To quickly and easily read out in a recognizable manner information on an individual who has committed an illegal act from an electronic watermark, when distributing an audio signal with the electronic watermark added so as not to degrade quality of the audio.SOLUTION: A decoding device 1 is equipped with a first input section 1a, a second input section 1b, a decoding section 1c, and a subtraction section 1d. The first input section 1a accepts input of a distributed audio signal to which specific information identifying an individual to whom the audio signal is delivered is added as a digital watermark, encoded, and delivered. The second input section 1b accepts input of the audio signal. The decoding section 1c decodes the distributed audio signal. The subtraction section 1d reads out the specific information by subtracting the audio signal from the decoded audio signal that is the signal decoded by the decoding section 1c.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a decoding device, an audio distribution system, a decoding method, and a program. [Background technology]

[0002] Patent Document 1 describes a digital watermarking device that can minimize degradation in audio quality of an audio signal to which digital watermark information has been added. The digital watermarking device converts an input stereo signal into a frequency domain signal, aligns a set of time and frequency axes of the converted signal with a set of two axes of a two-dimensional image as a digital watermark, and then adds the two-dimensional image as a digital watermark to the converted signal. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-022114 Summary of the Invention [Problem to be solved by the invention]

[0004] When distributing copyrighted paid audio content, it is necessary to prevent and suppress illegal activities such as illegal duplication and unauthorized redistribution. The same applies to copyrighted audio content distributed free of charge. Furthermore, if information that identifies the recipient's personal information is embedded in the audio content as a digital watermark and the content is distributed, and if the fact that the digital watermark is embedded becomes widely known, it will help to deter illegal activities.

[0005] Therefore, there is a need for a technology that can quickly and easily read out digital watermarks that prevent illegal activities from being committed in audio content that is distributed with digital watermarks added so as not to degrade the audio quality. That is, there is a need for a technology that allows the source of audio content to quickly and easily check information that identifies individuals who have committed illegal activities from the digital watermarks in the distributed content. Note that while the technology described in Patent Document 1 can add digital watermarks to audio content so as not to degrade the audio quality, it cannot address these issues.

[0006] The object of the present disclosure is to provide a decoding device, an audio distribution system, a decoding method, and a program that solve the above-mentioned problem. The above-mentioned problem is to enable, when distributing an audio signal to which a digital watermark has been added so as not to degrade the audio quality, to quickly and easily read out information on individuals who have committed illegal acts from the digital watermark in a recognizable manner. [Means for solving the problem]

[0007] A decoding device according to a first aspect of the present disclosure includes a first input unit that inputs a distributed audio signal in which specific information identifying an individual recipient is added to the audio signal as an electronic watermark, and the encoded and distributed audio signal is then transmitted; a second input unit that inputs the audio signal; a decoding unit that decodes the distributed audio signal; and a subtraction unit that reads out the specific information by subtracting the audio signal from a decoded audio signal that is the signal decoded by the decoding unit.

[0008] A decoding method according to a second aspect of the present disclosure involves inputting a distributed audio signal in which specific information identifying an individual recipient has been added as an electronic watermark to the audio signal, encoding the signal, and distributing the encoded audio signal; inputting the audio signal, decoding the distributed audio signal, and subtracting the audio signal from the decoded audio signal, thereby reading out the specific information.

[0009] A program according to a third aspect of the present disclosure is a program for causing a computer to execute a process of inputting a distributed audio signal in which specific information identifying an individual to whom the audio signal is distributed has been added as an electronic watermark, encoded, and distributed, inputting the audio signal, decoding the distributed audio signal, and subtracting the audio signal from the decoded audio signal, thereby reading out the specific information. [Effects of the Invention]

[0010] The present disclosure makes it possible to quickly and easily read out information about individuals who have committed illegal acts from the watermark in a recognizable manner when distributing an audio signal to which a digital watermark has been added so as not to degrade the audio quality. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a block diagram showing an example of the configuration of a decoding device according to the first embodiment. [Figure 2] FIG. 10 is a block diagram showing an example of the configuration of an encoding device in an audio distribution system according to a second embodiment. [Figure 3] FIG. 10 is a block diagram showing an example of the configuration of a decoding device in an audio distribution system according to a second embodiment. [Figure 4] FIG. 10 is a block diagram showing a digital watermark adding device according to a comparative example. [Figure 5] 3 is a block diagram showing an example of the configuration of a digital watermark adding unit in the encoding device of FIG. 2. FIG. [Figure 6] 6 is a block diagram showing an example of the configuration of a phase converter in the digital watermark adding unit of FIG. 5. FIG. [Figure 7] 6 is a block diagram showing an example of the configuration of a phase controller in the digital watermark adding unit of FIG. 5. FIG. [Figure 8] 7 is a diagram illustrating an example of phase control in the phase converter of FIG. 6. FIG. [Figure 9] 4 is a block diagram showing an example of the configuration of a digital watermark display unit in the decoding device of FIG. 3. FIG. [Figure 10] FIG. 2 is a diagram illustrating an example of a spectrogram of an original audio signal. [Figure 11] FIG. 10 is a diagram showing an example of a spectrogram of an audio signal to which a digital watermark has been added. [Figure 12] FIG. 10 is a diagram showing an example of a display of a digital watermark. [Figure 13] FIG. 2 illustrates an example of a hardware configuration included in the device. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments will be described with reference to the drawings. Note that in the embodiments, identical or equivalent elements are given the same reference numerals, and redundant explanations may be omitted. Furthermore, although some of the drawings described below depict unidirectional arrows, these arrows simply indicate the direction of flow of a certain signal (data), and do not exclude bidirectionality.

[0013] <Embodiment 1> The decoding device according to the first embodiment will be described with reference to Fig. 1. Fig. 1 is a block diagram showing an example of the configuration of the decoding device according to the first embodiment.

[0014] As shown in FIG. 1, a decoding device 1 according to this embodiment includes a first input unit 1a, a second input unit 1b, a decoding unit 1c, and a subtraction unit 1d.

[0015] The first input unit 1a receives a distribution audio signal. This distribution audio signal is an audio signal (original audio signal) to which specific information identifying an individual recipient has been added as a digital watermark, and then the signal is encoded and distributed.

[0016] The process of adding a digital watermark and the process of encoding can be performed by an encoding device (not shown), and the distribution process can be performed by a distribution device (not shown) or a distribution unit provided in the encoding device. The decoding device 1, together with the encoding device and the distribution device or the encoding device provided with a distribution unit, constitutes an audio distribution system.

[0017] Furthermore, the specific information added to the digital watermark can be information acquired by the encoding device, such as the ID of the user who has made the distribution request, the ID of the terminal used by the user, etc. Alternatively, this specific information can be information acquired from the distribution request source in this way and processed (such as by extracting a portion).

[0018] In the decoding device 1 according to this embodiment, a second input unit 1b further inputs the original audio signal. A decoding unit 1c decodes the distributed audio signal. A subtraction unit 1d subtracts the original audio signal from a decoded audio signal, which is a signal decoded by the decoding unit 1c, to read the specific information.

[0019] In other words, the subtraction unit 1d can extract the information identifying the individual recipient that was added as an electronic watermark from the distributed audio signal by the simple process of subtraction, making it possible to quickly and easily confirm illegal activity.

[0020] The decoding device 1 may have a control unit (not shown) that controls the entire device. This control unit may be realized, for example, by a CPU (Central Processing Unit), a working memory, and a non-volatile storage device that stores a program (firmware, etc.) that executes the above-mentioned processes. This control unit may be partly or entirely an integrated circuit. The above-mentioned encoding device (or distribution device) may also have a control unit (not shown) that controls the entire device. This control unit may be realized, for example, by a CPU, a working memory, and a non-volatile storage device that stores a program that executes the above-mentioned addition and encoding processes (or distribution processes). This control unit may be partly or entirely an integrated circuit.

[0021] As described above, according to this embodiment, when an audio signal to which a digital watermark has been added is distributed so as not to degrade the audio quality, information on an individual who has engaged in illegal activity can be read from the digital watermark in a manner that is quickly and easily recognizable. As a result, according to this embodiment, the distributor can quickly and easily check whether or not illegal activity has occurred, i.e., check the digital watermark.

[0022] As an example of application of this embodiment, a unique watermark such as a serial number can be easily inserted each time content is distributed in software for audio content creation tools or in communication equipment at content distribution stations and broadcasting stations. Therefore, in this example of application, if audio content is spread after distribution, it is possible to identify where and by whom it was leaked, which will ultimately lead to a check on illegal duplication and unauthorized redistribution (illegal redistribution).

[0023] <Embodiment 2> The second embodiment will be described mainly focusing on the differences from the first embodiment, but various examples described in the first embodiment can also be applied. First, an audio distribution system according to the second embodiment will be described with reference to Fig. 2 and Fig. 3. Fig. 2 is a block diagram showing an example of the configuration of an encoding device in the audio distribution system according to the second embodiment. Fig. 3 is a block diagram showing an example of the configuration of a decoding device in the audio distribution system according to the second embodiment.

[0024] The audio distribution system according to this embodiment can be configured to include an encoding device 10 shown in FIG. 2 and a decoding device 20 shown in FIG.

[0025] 2, the encoding device 10 can include a digital watermark adding unit 11 and an audio encoding unit 12. Note that the digital watermark adding unit 11 and the audio encoding unit 12 can also function as standalone devices, functioning as a digital watermark adding device and an audio encoder, respectively. However, for example, some or all of these components can also be installed in the encoding device 10 as a control unit controlled by a program.

[0026] The digital watermark adding unit 11 receives an original audio signal s10, which is a signal of the original audio content, and an information signal s11, which indicates specific information for identifying an individual recipient. The original audio signal s10 may be, for example, a PCM (Pulse Code Modulation) audio signal. The specific information may be, for example, a user ID for a paid content contract, but may also include a content ID, a content provider ID, a service provider ID, etc. The information signal s11 may be an input image signal in which the specific information for identifying an individual recipient is depicted as a two-dimensional image.

[0027] The digital watermark adding unit 11 adds an information signal s11 indicating specific information to the original audio signal s10, and outputs the added audio signal s12 to the audio encoding unit 12. The audio signal s12 may also be, for example, a PCM audio signal. The audio encoding unit 12 compression-encodes the audio signal s12 into MP3, AAC, or the like, and outputs it as a distribution signal (encoded audio signal) s13. The encoding device 10 includes a communication unit (not shown), and distributes the distribution signal s13 to a distribution destination from this communication unit.

[0028] 3, the decoding device 20 may include an audio decoding unit 21, a subtraction unit 22, and a digital watermark display unit 23. The audio decoding unit 21, the subtraction unit 22, and the digital watermark display unit 23 may be devices that function independently as an audio decoder, a subtractor, and a digital watermark display unit, respectively. However, for example, some or all of these components may be installed in the decoding device 20 as a control unit controlled by a program.

[0029] The distribution signal s13 distributed from the encoding device 10 is a signal obtained by compressing and encoding audio content with a digital watermark, and will be described here as a compressed and encoded signal s20. The decoding device 20 includes a communication unit and a storage unit (not shown), and is configured to receive the compressed and encoded signal s20 via the communication unit and to obtain the original audio signal s21 (s10) from the storage unit.

[0030] The audio decoding unit 21 receives the compressed encoded signal s20, decodes it into MP3, AAC, etc., and outputs the resulting audio signal s22 with specific information added (for example, a PCM audio signal with specific information added). The subtraction unit 22 subtracts the delivered original audio signal s21 (s10) from the signal s22 to obtain a subtraction signal s23, and outputs the subtraction signal s23 to the digital watermark display unit 23.

[0031] The digital watermark display unit 23 displays a digital watermark based on the input subtraction signal s23. When specific information that expresses information that identifies an individual recipient in a two-dimensional image is added as a digital watermark, the digital watermark display unit 23 is an example of a display unit that displays the specific information read out by the subtraction unit 22 as a two-dimensional image. The subtraction signal s23 is a signal in which the digital watermark is emphasized by the subtraction unit 22, so that the digital watermark display unit 23 can display the specific information as easy-to-check information.

[0032] (Digital watermark adding unit 11 of encoding device 10) It is preferable that the digital watermark cannot be easily removed without degrading the audio quality at the destination, and it is preferable that the digital watermark adding unit 11 has a configuration that satisfies this requirement. In other words, when the digital watermark adding unit 11 adds (imprints) specific information to the audio signal, it is preferable that the specific information be added in an inconspicuous manner as sound, and that the digital watermark be difficult to remove at the destination.

[0033] Before describing a specific example of the configuration of such a digital watermark adding unit 11, a digital watermark adding device according to a comparative example will be described with reference to Fig. 4. Fig. 4 is a block diagram showing a digital watermark adding device according to the comparative example.

[0034] 4 includes a low-pass filter 91 and a digital watermark adder 92. The low-pass filter 91 suppresses high-frequency signals from an input original audio signal s90 to generate a low-frequency signal (band-limited signal) s92, which it outputs to the digital watermark adder 92. The digital watermark adder 92 receives an input of a digital watermark signal s91, which expresses digital watermark information using high-frequency amplitude values ​​or the like, adds the digital watermark signal s91 to the low-frequency signal s92 input from the low-pass filter 91, and outputs an audio signal s93 to which a digital watermark has been added.

[0035] If the digital watermark signal s91 is generated at a high frequency (e.g., 15 kHz or higher) that is difficult for humans to hear, the signal will not stand out as audible sound, and degradation of audio quality can be avoided. However, if the audio content is copied using analog equipment that cuts high frequencies, the digital watermark will be lost. Furthermore, since the digital watermark in this audio signal s93 can be easily removed without degrading the audio quality, it is not suitable for use as a digital watermark for the purpose of protecting the copyright of audio content.

[0036] A specific example of the configuration of the digital watermark adding unit 11 in Fig. 2 will be described with reference to Fig. 5. Fig. 5 is a block diagram showing an example of the configuration of the digital watermark adding unit 11 in the encoding device 10 in Fig. 2.

[0037] 5, the digital watermark adding unit 11 can include a frequency analyzer 31, a phase controller (phase control circuit) 32, a plurality of phase converters 33-0 to 33-n, and a frequency synthesizer 34. For simplicity of explanation, a monaural audio signal is described here. In the case of a multi-channel audio signal, for example, each channel may be provided with a frequency analyzer 31, a plurality of phase converters 33-0 to 33-n, and a frequency synthesizer 34.

[0038] The frequency analyzer 31 receives the original audio signal s31 (s10, s21) as input, and outputs frequency-analyzed frequency component signals (frequency analysis output signals) s35-0 to s35-n to phase converters 33-0 to 33-n provided corresponding to each frequency.

[0039] Phase controller 32 receives digital watermark signal s33 (s11), which is image data indicating specific information, and controls phase converters 33-0 to 33-n to add the digital watermark signal using pixel-dependent control signals (phase control signals) s34-0 to s34-n. Phase converters 33-0 to 33-n receive frequency component signals s35-0 to s35-n, respectively, and add the digital watermark signal by changing the phase of frequency component signals s35-0 to 35-n in accordance with pixel-dependent control signals s34-0 to s34-n. Phase converters 33-0 to 33-n output signals (phase-transformed output signals) s36-0 to s36-n, each with the digital watermark signal added, to frequency synthesizer 34.

[0040] The frequency synthesizer 34 synthesizes the signals (phase-transformed output signals) s36-0 to s36-n output from the phase converters 33-0 to 33-n, respectively, and outputs a signal s32 (s12) to which a digital watermark has been added.

[0041] Next, a configuration example of the phase converters 33-0 to 33-n will be described with reference to Fig. 6. Fig. 6 is a block diagram showing a configuration example of each phase converter in the digital watermark adding unit 11 of Fig. 2 and Fig. 5, and Fig. 6 shows phase converter 33-n as a representative.

[0042] 6, the phase converter 33-n can include a phase shift control switch 331-n and a phase shifter 332-n. The phase converter 33-n receives the frequency component signal s35-n and the pixel-dependent control signal s34-n as input, and passes them to the phase shift control switch 331-n and the phase shifter 332-n. The phase converter 33-n shifts the phase of the frequency component signal s35-n in the phase shifter 332-n via the phase shift control switch 331-n, and outputs a phase-converted output signal s36-n.

[0043] Specifically, the phase shifter 332-n shifts the phase of the frequency component signal s35-n in accordance with the control signal s34-n and outputs the phase-shifted signal s37 to the phase shift control switch 331-n. The phase shift control switch 331-n selects either the frequency component signal s35-n or a signal s37 obtained by shifting the phase of the frequency component signal s35-n in accordance with the control signal s34-n, and outputs the selected signal as the phase-converted output signal s36-n.

[0044] Next, an example of the configuration of the phase controller 32 will be described with reference to Fig. 7. Fig. 7 is a block diagram showing an example of the configuration of the phase controller 32 in the digital watermark adding unit 11 of Figs.

[0045] 7, phase controller 32 can include a plurality of phase determination units 320-0 to 320-n. Phase controller 32 receives an electronic watermark signal s33, which is image data, as input. This input is directed to phase determination units 320-0 to 320-n. Phase determination units 320-0 to 320-n each determine a phase control signal for phase converters 33-0 to 33-n that corresponds to a frequency component corresponding to a pixel, and output the determined phase control signal to phase converters 33-0 to 33-n.

[0046] Next, an example of phase control will be described with reference to Fig. 8. Fig. 8 is a diagram showing an example of phase control in phase converter 33-n of Fig. 6. As illustrated in Fig. 8, control signals s34-0 to s34-n can be determined in phase determination units 320-0 to 320-n, respectively, as follows, for example. Of course, the description here is just one example, and the same applies to other phase converters 33-0, etc.

[0047] In this example, for points that are desired to be displayed as the whitest pixels in the digital watermark, the control signal s34-n is a signal that performs the following control. That is, this signal turns on the phase shift control switch 331-n and sets the phase shift amount in the phase shifter 332-n to 0 [rad]. Conversely, for points that are desired to be displayed as the blackest, the control signal s34-n turns on the phase shift control switch 331-n and sets the phase shift amount in the phase shifter 332-n to π [rad]. Note that for points where there are no pixels, the control signal s34-n turns off the phase shift control switch 331-n and sets the phase shift amount in the phase shifter 332-n to 0 [rad]. This is to output the original signal as is at points where there are no pixels.

[0048] As described above, the encoding device 10 according to this embodiment may include an analysis unit exemplified by the frequency analyzer 31, a conversion unit exemplified by the phase converters 33-0 to 33-n, and an output unit exemplified by the frequency synthesizer 34 and audio encoding unit 12. The analysis unit performs frequency analysis of the audio signal and outputs the result for each frequency component. The conversion unit associates the position of a pixel in a two-dimensional image, which is specific information, with a two-dimensional region represented by the frequency axis and time axis obtained by the frequency analysis of the audio signal, and phase-shifts the frequency component signals of the audio signal corresponding to the pixel position in accordance with the shading of the pixel. The output unit outputs a digital watermarked signal, obtained by combining all the frequency component signals for each channel, to a distribution device as a distribution audio signal.

[0049] (Principle of digital watermark addition processing in encoding device 10) The operating principle of the additional processing will be explained by taking the frequency analyzer 31 as a typical FFT (Fast Fourier Transform) calculator and the frequency synthesizer 34 as an inverse FFT calculator.

[0050] The complex signal output from the FFT calculator is represented by L[n], where a[n] is the real component and b[n] is the imaginary component. L[n]=a[n]+b[n]j (1)

[0051] Here, n is the number of the frequency component and is an integer of 0, 1, 2, . . . , n. For the frequency component signal to be added as an image signal, the phase angle φ[n] to be shifted is calculated using equation (2).

[0052]

number

[0053] Here, z[n] is a value indicating the brightness (or gradation) of the digital watermark pixel to be displayed, and 0≦z[n]≦2. For example, when z[n] is "0", it is the value desired to be displayed as the blackest, and φ[n]=π. When z[n] is "2", it is the value desired to be displayed as white, and φ[n]=0.

[0054] The generated signal L'[n] is obtained by shifting the phase of the signal L[n] by φ[n], and is shown in equation (3).

[0055] L'[n]=(a[n]*cosφ[n]-b[n]*sinφ[n])+(a[n]*sinφ[n]+b[n]*cosφ[n])j ···(3)

[0056] These calculations are performed for each FFT point, then synthesized using an inverse FFT, and output as an audio signal. By repeating this process every unit time, the digital watermark data image is added.

[0057] (Digital watermark display unit 23 of decoding device 20) An example of the configuration of the digital watermark display unit 23 that displays the digital watermark will be described with reference to Fig. 9. Fig. 9 is a block diagram showing an example of the configuration of the digital watermark display unit 23 in the decoding device 20 of Fig. 3.

[0058] 9, the digital watermark display unit 23 can be exemplified by a spectrogram display unit 43 including a frequency analyzer 44 and a grayscale display unit 45. In FIG. 9, a subtractor 42 is an example of the subtraction unit 22.

[0059] The subtractor 42 subtracts the audio signal s42 (s22) to which the digital watermark signal has been added from the original audio signal s41 (s21) to which the digital watermark signal has not been added. Of course, the subtraction is similar when subtracting the signal s42 from the signal s41. The subtractor 42 outputs the subtracted signal s43 to the frequency analyzer 44 of the spectrogram display unit 43. The frequency analyzer 44 analyzes the subtracted signal s43 and outputs frequency component signals (frequency analysis output signals) s44-0 to s44-n to a shading display unit (frequency component display unit) 45.

[0060] The shading display 45 receives the frequency component signals s44-0 to s44-n and displays shading according to the power of each frequency component. The spectrogram display 43 is an example of a display unit that performs frequency analysis on the signal resulting from the subtraction performed by the subtractor 42 and displays the power of the frequency components in gradation in a two-dimensional area represented by the frequency axis and the time axis.

[0061] (Principle of digital watermark display processing in the decoding device 20) The operating principle of the display process will be explained by taking the frequency analyzer 44 as a typical FFT (Fast Fourier Transform) calculator and the frequency synthesizer provided in the gradation display device 45 as an inverse FFT calculator.

[0062] When the digital watermark is displayed, the digital watermarked signal L'[n] is subtracted from the original audio signal L[n].

[0063] In the previous example, when z[n]=2, which is the whitest possible display, φ[n]=0, so according to equation (4), it becomes 0 and the spectral component disappears.

[0064] (L[n]-L'[n]) / 2 ={a[n]+b[n]j-(a[n]*cosφ[n]-b[n]*sinφ[n])-(a[n]*sinφ[n]+b[n]*cosφ[n])j} / 2 =(a[n]+b[n]ja[n]-b[n]j) / 2 =0 ···(4)

[0065] Furthermore, when z[n]=0, which is the darkest possible display, φ[n]=π, and therefore, according to equation (5), the original signal L[n] remains unchanged.

[0066] (L[n]-L'[n]) / 2 ={a[n]+b[n]j-(a[n]*cosφ[n]-b[n]*sinφ[n])-(a[n]*sinφ[n]+b[n]*cosφ[n])j} / 2 =(a[n]+b[n]j+a[n]+b[n]j) / 2 =a[n]+b[n]j=L[n] ···(5)

[0067] The audio signal synthesized using the above operating principle is displayed as a power spectrogram using FFT calculations, allowing the digital watermark to emerge as image information.

[0068] (Example of operation) Next, an example of the operation of such an audio distribution system will be briefly described. As explained with reference to Fig. 5, the digital watermarking unit 11 decomposes the original audio signal s31 into frequency components using the frequency analyzer 31, and outputs the decomposed frequency component signals s35-0 to 35-n to the phase converters 33-0 to 33-n provided for each frequency. Here, n is an identification symbol for the frequency component number. The output frequency component signals s35-0 to 35-n correspond to equation (1).

[0069] 6, phase converter 33-n receives frequency component signal s35-n as input, and phase shifter 332-n shifts the phase of frequency component signal s35-n via phase shift control switch 331-n to obtain phase-converted output signal s36-n. The same applies to other phase converters such as phase converter 33-0. Phase-converted output signals s36-0 to s36-n correspond to equation (3).

[0070] The phase shift here is controlled by the value from phase controller 32 as described above. As explained in Fig. 7, phase controller 32 receives image signal s33, which becomes a digital watermark. Then, phase controller 32 provides, to each of phase converters 33-0 to 33-n, ON / OFF of a phase shift control switch that performs bypass control and a phase shift amount based on the pixel gray value for the frequency component at a position corresponding to a pixel point in image signal s33. An example of phase control of phase converters 33-0 to 33-n in phase controller 32 is as explained with reference to Fig. 8.

[0071] The audio content distributed to the recipient in this way may be distributed through illegal activities by individuals at the recipient's end. When displaying a digital watermark on distributed audio content, the audio content is first acquired by the decryption device 20 and then executed.

[0072] As shown in Figure 9, a subtractor 42 subtracts an audio signal s42 with a digital watermark added from an original audio signal s41 with no digital watermark added. The subtracted signal s43 is decomposed into signals for each frequency component by a frequency analyzer 44 in a spectrogram display 43, and a gradation display (frequency component power display) 45 calculates the power and displays it as image gradation or brightness. An example of this display is as shown in equations (4) and (5). Frequency analysis and display are repeated for each fixed frame time, and a two-dimensional image with frequency on the vertical axis and time on the horizontal axis is displayed on the display screen of the gradation display 45.

[0073] As specific display examples, display examples of spectrograms of digital watermark signals will be described with reference to Fig. 10 to Fig. 12. Fig. 10 is a diagram showing an example of a spectrogram of an original audio signal s41, and Fig. 11 is a diagram showing an example of a spectrogram of an audio signal s42 to which a digital watermark has been added. Fig. 12 is a diagram showing a display example of a digital watermark signal s43 included in the audio signal s42 in Fig. 11.

[0074] 10 to 12, signals with strong frequency components are displayed in black, and signals with weak frequency components are displayed in white. Even when a signal with a digital watermark added is displayed as shown in FIG. 11, the digital watermark image data cannot be recognized. This indicates that there is little degradation of the audio signal. Furthermore, when the digital watermarked audio signal s42 is subtracted from the original audio signal s41, the resulting signal (i.e., the digital watermark signal) s43 has an easily recognizable digital watermark image, as shown in the spectrogram in FIG. 12. That is, when the signal s43 is displayed, the digital watermark image (e.g., a character image) can be recognized as a black image that stands out overall at the bottom (low frequency position), as shown in FIG.

[0075] 10 to 12 show examples of application to 2ch audio signals, rather than the configuration described above, which is premised on a monaural signal, and in this case, each device in each block diagram described above should be configured so that it can process both Lch and Rch signals. Of course, it goes without saying that it is also possible to configure the device to support multiple channels other than 2ch.

[0076] As described above, according to this embodiment, in a device (decoding device 20) that displays or detects a digital watermark, the method for displaying the digital watermark is simple, and the digital watermark can be easily identified (confirmed). Furthermore, the encoding device 10 adds specific information to audio content as a digital watermark, and even if the audio content is copied, the specific information is not lost, and degradation of audio quality of the audio signal to which the specific information has been added can be reduced. Furthermore, removing the digital watermark from an audio signal encoded by the encoding device 10 significantly deteriorates the audio quality, making removing the digital watermark meaningless.

[0077] As described above, according to this embodiment, when distributing an audio signal to which a digital watermark has been added so as not to degrade the audio quality, information on individuals who have engaged in illegal activities can be read from the digital watermark in a manner that is quickly and easily recognizable. As a result, this embodiment enables the distributor to quickly and easily check for illegal activities, i.e., check the digital watermark. Therefore, this embodiment can be said to be effective in preventing and suppressing illegal activities such as illegal duplication and unauthorized redistribution in the distribution of audio content.

[0078] <Other embodiments> Each of the devices described in the first and second embodiments can have the following hardware configuration: Fig. 13 is a diagram showing an example of the hardware configuration included in the device.

[0079] 13 is one of the devices according to the first and second embodiments, and includes a processor 101, a memory 102, and a communication interface 103. The functions of the components in the devices described in the first and second embodiments can be realized by the processor 101 reading a program stored in the memory 102 and executing the program in cooperation with the communication interface 103.

[0080] The programs incorporated into the decoding device and the encoding device are programs that cause a computer to execute the processes described as the decoding process and the encoding process, respectively, and other examples are as described in each embodiment.

[0081] The program includes instructions (or software code) that, when loaded into a computer, cause the computer to perform one or more functions described in the embodiments. The program may be stored in a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, computer-readable media or tangible storage media include random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technology, CD-ROM, digital versatile disc (DVD), Blu-ray disc or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage device. The program may also be transmitted on a transitory computer-readable medium or communication medium. By way of example and not limitation, transitory computer-readable media or communication media include electrical, optical, acoustic, or other forms of propagated signals.

[0082] The present disclosure is not limited to the above-described embodiments, and may be modified as appropriate without departing from the spirit and scope of the present disclosure. In addition, the present disclosure may be implemented by appropriately combining the respective embodiments. [Explanation of symbols]

[0083] 1, 20 Decoding device 1a First input section 1b Second input section 1c Decoding section 1d, 22 subtraction section 10 Encoding device 11 Digital watermark adding unit 12 Audio Encoding Unit 21 Audio Decoding Unit 23 Digital watermark display section 31 Frequency Analyzer 32 Phase Controller 33-0, 33-1, 33-n phase converter 34 Frequency Synthesizer 42 Subtractor 43 Spectrogram Display 44 Frequency Analyzer 45 Grayscale indicator 91 Low-pass filter 92 Digital Watermark Adder 100 devices 101 processors 102 memory 103 Communication Interface 320-0, 320-1, 320-n phase determining section 331-n phase shift control switch 332-n phase shifter

Claims

1. A system comprising a decoding device, an encoding device, and a distribution device, The decoding device a storage unit for storing an original audio signal; an input unit that inputs a delivery audio signal in which specific information representing information identifying an individual of a delivery destination in the form of a two-dimensional image is added as a digital watermark to the original audio signal stored in the storage unit, the encoded signal is delivered to a device used by the individual of the delivery destination, which is a device different from the decoding device; an acquisition unit that acquires the original audio signal from the storage unit; a decoding unit that decodes the delivery audio signal input by the input unit; a subtraction unit that subtracts the original audio signal acquired from the storage unit by the acquisition unit from a decoded audio signal that is a signal decoded by the decoding unit, thereby reading out the specific information; a display unit that displays the specific information read by the subtraction unit as a two-dimensional image; wherein the display unit performs frequency analysis on the signal resulting from the subtraction performed by the subtraction unit, and displays the power of the frequency components in a two-dimensional area represented by a frequency axis and a time axis, the encoding device adds the specific information to the original audio signal as the digital watermark and performs encoding; the distribution device distributes the distribution audio signal, which is the signal encoded by the encoding device, to the distribution destination device; Audio distribution system.

2. The encoding device an analysis unit that performs frequency analysis on the original audio signal and outputs the result for each frequency component; a conversion unit that associates pixel positions of the two-dimensional image, which is the specific information, with a two-dimensional region represented by a frequency axis and a time axis obtained by the frequency analysis of the original audio signal, and phase-shifts frequency component signals of the original audio signal corresponding to the pixel positions in accordance with the shading of the pixels; an output unit that outputs a digital watermark-added signal obtained by synthesizing all frequency component signals for each channel to the distribution device as the distribution audio signal; Equipped with 10. The audio distribution system of claim 1.

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