JPH11316599A - Electronic watermark embedding device, audio encoding device, and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To actualize an electronic watermak insertion technology suitable for the encoding process of digital audio data. SOLUTION: This embedding device is equipped with a circuit 11 which converts audio data to a frequency range, a quantizing circuit 12 which quantizes the audio data converted to the frequency range, and a reversible substituting process circuit 13 which replaces part of the quantized audio data reversibly with another data value and inserts electronic watermark information 16 into the audio data having been converted from the signal of the time area to the signal of the frequency area and quantized when the quantized audio data are replaced reversibly with another data value, so that the embedded electronic watermark information 16 is not truncated in the quantizing process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital watermark embedding device, an audio encoding device using the same, and a recording medium storing a program for realizing the digital watermark embedding device. Alternatively, it is suitable for use in an audio encoding device for storing in a recording medium.

[0002]

2. Description of the Related Art With the recent development of computer networks and the spread of inexpensive and high-performance computers, the exchange of digital data on networks has become active. However, since digital data has the property that a complete copy can be created easily and in large quantities, it indicates the possibility that a copy of the same quality as the original can be illegally created and redistributed. Thus, it is considered that the copyright of the creator of the digital data is infringed.

Therefore, as a method for preventing such copyright infringement, a method using an electronic watermark (hereinafter referred to as an electronic watermark) has been proposed. The digital watermark is a predetermined identifier embedded in digital data such as an audio signal and an image signal. That is, the digital watermark is used for the purpose of protecting the rights of the copyright owner, for example, by embedding information such as the copyright owner in the original digital data.

As a conventional method of inserting a digital watermark into audio data, for example, LFTurner “Digital
As stated in the US patent for Data Security System,
For digital data that is randomly selected from digital audio data sampled at a constant frequency in the time domain, an insignificant bit (i.e., one or more bits located at the lowest part of the word of the audio sample). It is proposed that the identifier be inserted into the digital audio data by replacing the given identifier with a predetermined identifier (electronic watermark information).

[0005]

Digital audio data is often subjected to an encoding process in order to reduce a huge amount of data. The encoding process currently mainly used is MDCT (Modified Discrete Co.).
In many cases, such as sine transform, a process that converts a signal in the time domain into a signal in the frequency domain is used. In this encoding process, in order to reduce the amount of data, a quantization process, which is an irreversible process, is performed on audio data in the frequency domain.

The quantization process is a process of extracting upper n bits (N and n are integers) of N bits of audio data and cutting off lower m bits (m = N−n). Therefore, the above-described LFTurner embedding method has a problem that an identifier inserted as a digital watermark in a lower part of audio data in a time domain is lost during encoding processing.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and has as its object to realize a digital watermark insertion method suitable for digital audio data encoding processing.

[0008]

SUMMARY OF THE INVENTION A digital watermark embedding apparatus according to the present invention inserts digital watermark information into audio data which has been converted from a time domain signal into a frequency domain signal and subjected to quantization processing. It is characterized by having done. Here, the digital watermark information may be inserted in the process of reversibly replacing the quantized audio data with another data value. Further, the digital watermark information may be additional information that is separately transmitted when the quantized audio data is reversibly replaced with another data value.

According to another aspect of the present invention, there is provided means for determining the perceptual importance of each frequency component of the audio data converted into the frequency domain signal, wherein the data of the frequency component which is important with respect to human hearing characteristics is provided. The electronic watermark information is inserted into the information. Here, the means for determining the perceptual importance of each frequency component of the audio data is based on the bit allocation information for each sub-band obtained by dividing the frequency component of the audio data. May be included, and the digital watermark information may be inserted into the data in the selected sub-band. Further, the means for determining the auditory importance of each frequency component of the audio data further includes a maximum value detection means for detecting data having a maximum value in the sub-band selected by the sub-band selection means, The digital watermark information may be inserted into the data of the maximum value.

[0010] Also, the audio encoding apparatus of the present invention comprises:
Audio encoding device having time / frequency conversion means for converting audio data into a frequency domain using time / frequency conversion processing, and quantization means for performing a quantization processing on the audio data converted into the frequency domain A digital watermark embedding unit for inserting digital watermark information into the quantized audio data. Here, there is provided a reversible replacement means for reversibly replacing the quantized audio data with another data value, the reversible replacement means also serving as the digital watermark embedding means, and converting the quantized audio data into The digital watermark information may be inserted when reversibly replacing with another data value.

In another aspect of the present invention, the digital watermark embedding means includes means for determining the perceptual importance of each frequency component of the audio data converted into the frequency domain signal. The digital watermark information is inserted into important frequency component data. Here, the means for determining the perceptual importance of each frequency component of the audio data is based on the bit allocation information for each sub-band obtained by dividing the frequency component of the audio data. And a digital watermark embedding means for inserting the digital watermark information into the data in the selected subband. Further, the means for determining the auditory importance of each frequency component of the audio data further includes a maximum value detection means for detecting data having a maximum value in the sub-band selected by the sub-band selection means, The digital watermark embedding means may insert the digital watermark information into the maximum value data. Further, the digital watermark information may be separately transmitted as additional information of data obtained by reversibly replacing the quantized audio data. Further, with respect to the frequency components whose audio data has been truncated to “0” data by the quantization process, information indicating that the frequency domain is “0” data is transmitted, and the “0” data is transmitted.
The digital watermark information may be inserted without performing the reversible replacement processing on the data.

Further, the computer-readable recording medium of the present invention separates the quantized audio data from audio data which has been converted from a time domain signal into a frequency domain signal and subjected to quantization processing. A program for causing a computer to function as means for inserting digital watermark information in a process of reversibly replacing the data value with the data value.

According to another aspect of the present invention, there is provided means for determining the perceptual importance of each frequency component of the audio data converted to the frequency domain signal, wherein the data of the frequency component which is important with respect to human hearing characteristics is provided. A program for causing a computer to further realize a function as a means for inserting the digital watermark information.

Since the present invention comprises the above technical means, the embedded digital watermark information is not deleted by the quantization process. According to another feature of the present invention, when the digital watermark information embedded in the data of the frequency component that is important for the human auditory characteristics in the audio data is rewritten, the output obtained when the data is decoded is obtained. The sound tends to appear as a change or deterioration in sound quality.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below based on an embodiment. FIG. 1 is a block diagram showing an overall configuration of an audio encoding device which is an embodiment implementing a digital watermark embedding device of the present invention.

Various methods are known for encoding audio data. To achieve a high compression efficiency, a method of converting audio data into a signal in the frequency domain using time / frequency conversion and performing encoding in the frequency domain is often used. Examples of the time / frequency conversion include a method using a sub-band filter and an MDCT. For an overview of these encoding methods, see FURU, published in MACEL DEKKAR (New York), 1991.
“Adbance in Speech Signal Processing” edited by I & SONDHI
On page 109 to page 140.

In the following, description will be made based on the encoding method using the above MDCT as the time / frequency conversion. However, this is only an example, and the present invention is not limited to other time /
It is also possible to adapt to a method using frequency conversion. As an example of the MDCT encoding method, MPE
G-2 ISO / IEC13818-7 known as AAC can be mentioned. For an overview of the MPEG-2 AAC, see "ISO / IEC MPEG-2 Advance by M. Bosi et al.
d Audio Coding ”(Journal of the audio engineering
society, Vol 45 No. 10, pp789-814, October 1997).

In FIG. 1, a digital audio signal input via an input terminal 1 is supplied to an MDCT circuit 11 and an adaptive bit allocation circuit 14. MD
In the CT circuit 11, the input digital audio signal is converted from the time domain to the frequency domain, and the result is output to the quantization circuit 12.

On the other hand, the adaptive bit allocation circuit 14 calculates the perceptual importance of each frequency component of the input digital audio signal based on the auditory characteristics of a person, and allocates bits according to the importance. Is calculated. Here, more bits are allocated to frequency components that are important with respect to human auditory characteristics, and less bits are allocated to frequency components that are not important. The bit allocation information calculated here is supplied to the quantization circuit 12, the reversible replacement processing circuit 13
And output to the multiplexing circuit 15.

The quantization circuit 12 performs a quantization process on the audio data converted into the frequency domain by the MDCT circuit 11 based on the bit allocation information calculated by the adaptive bit allocation circuit 14. The quantization process means, for example, the upper n bits of N-bit audio data.
(N and n are integers) bits are taken out and the lower m (= N−
n) This is a process of truncating bits. The quantization process is generally performed by dividing a plurality of frequency components into several regions (subbands). Therefore, bit allocation information is also calculated for each subband.

The reversible replacement processing circuit 13 performs a process of reversibly replacing a part of the audio data quantized by the quantization circuit 12 with another data value. Some audio data converted into the frequency domain by the MDCT have a pulse-like maximum value in a subband. By reversibly replacing such data with values similar to the surrounding data and averaging the properties of the data in the subband, the efficiency of compression can be increased.

The reversible replacement processing of audio data in the frequency domain is described in Takamizawa et al., “Maximum Value Replacement Reversible Coding Method and Its Application to Audio Coding” (Transactions of the Institute of Electronics, Information and Communication Engineers, Vol. J80-A No.9 pp1388
-1395, 1997).

The reversible replacement processing circuit 13 also has a digital watermark embedding means for inserting the digital watermark information 16 into the audio data quantized by the quantization circuit 12. In other words, the digital watermark information 16 is inserted into the audio data during the process of reversibly replacing a part of the quantized audio data with another data value. In other words, the reversible replacement processing circuit 13 of the present embodiment performs the reversible replacement processing using the digital watermark information 16 as necessary.

In the reversible replacement process, the data of the replaced frequency component is sent to the multiplexing circuit 15, and the position information of the replaced frequency component and the information of the replaced value are multiplexed as additional information. It is sent to the circuit 15. The multiplexing circuit 15 multiplexes the audio data quantized in the frequency domain and subjected to the reversible replacement processing, the replacement position information, the replacement value information, and the bit allocation information, and outputs the multiplexed data via the output terminal 2. It is output as encoded data.

FIG. 2 is a block diagram showing one embodiment of the reversible replacement processing circuit 13 shown in FIG. In FIG. 2, the digital watermark information 16 is a first input terminal 21.
Is input to the terminal A of the first switch circuit 33 via the terminal A. The quantized audio data is input to the local maximum value search circuit 31, the replacement circuit 34, and the terminal B of the second switch circuit 35 via the second input terminal 22.
Further, the bit allocation information for each subband is input to the subband selection circuit 32 via the third input terminal 23.

The sub-band selection circuit 32 selects a sub-band having a large bit allocation information value, that is, a sub-band having a high perceptual importance, and outputs the result to the local maximum value search circuit 31. If one subband is to be selected, the subband with the largest bit allocation is selected from the subbands. When a plurality of subbands are to be selected (for example, four subbands), a plurality of subbands are selected from each subband in order from the one with the largest bit allocation.

The maximum value search circuit 31 selects the maximum value from the quantized audio data in the sub-band selected by the sub-band selection circuit 32, that is, the sub-band determined to be perceptually significant. The value is retrieved, and the detected maximum value is output to the terminal B side of the first switch circuit 33. Further, the detected position information of the maximum value is output to the outside (the multiplexing circuit 15 in FIG. 1) via the first output terminal 24.

The first switch circuit 33 includes: a digital watermark information 16 input through the first input terminal 21;
Either one of the maximum values in the selected subband searched by the maximum value search circuit 31 is selected and output. If a digital watermark is to be inserted into the audio data, the digital watermark information 16 is selected. Conversely, if no digital watermark is to be inserted, the maximum value is selected.

The digital watermark is inserted in accordance with a predetermined rule, for example, inserted once in a plurality of times of the maximum value search processing. The amount of watermark information inserted is 1 per second.
About 00 bytes or more are possible. The first switch circuit 33 switches the selection state to the terminal A side or the terminal B side according to this rule. When a plurality of subbands are selected by the subband selection circuit 32, a digital watermark is inserted into each of the subbands. The digital watermark may be inserted at random without following a predetermined rule.

The replacement value information (digital watermark information 16 or local maximum value) selected by the first switch circuit 33 is
Output to the replacement circuit 34 and the second output terminal 2
5 to the outside (multiplexing circuit 15 in FIG. 1). The replacement circuit 34 is configured by a subtraction circuit in the example of FIG. 2, and is selected by the first switch circuit 33 from the value of the quantized audio data input via the second input terminal 22. The value of the replaced value information is subtracted.
The result of the subtraction is output to the terminal A of the second switch circuit 35.

With this configuration, when the digital watermark is not inserted, the subtraction is performed using the maximum value selected by the first switch circuit 33. In this case, the replacement circuit 3
Since the same maximum value data is input to the two input terminals of No. 4, the subtraction result is "0", and the coding efficiency can be improved. On the other hand, when inserting a digital watermark, subtraction is performed using the value of the digital watermark information 16 selected by the first switch circuit 33. This means that the digital watermark is embedded in the encoded data.

For the frequency components whose audio data has been truncated to "0" data by the quantization process, information indicating that the frequency domain is "0" data is transmitted. The digital watermark information 16 is inserted without performing a reversible replacement process.

As described above, since the subtraction is used in the replacement process, it is possible to reversibly reverse the data value on the decoding side (not shown) and restore the original value. Although a subtraction circuit is used here, other arithmetic processing may be performed as long as the data value can be reversibly reversed and returned to the original value.

As is clear from the above, the replacement circuit 34 of the present embodiment also has a digital watermark embedding circuit. Therefore, in the present embodiment, it is possible to embed a digital watermark by using the replacement circuit 34 that may be used in a conventional audio encoding device, and it is possible to suppress an increase in the size of the device.

The second switch circuit 35 selects one of the output of the replacement circuit 34 input to the terminal A side and the quantized audio data input to the terminal B side. The signal is output to the outside (the multiplexing circuit 15 in FIG. 1) via the output terminal 26. The terminal A is selected at the position where the maximum value is detected. On the other hand, at a position other than the maximum value, the terminal B side is selected, and data that has not undergone the reversible replacement processing, that is, the quantized audio data itself is output to the outside.

As described above in detail, in this embodiment, since the digital watermark information is inserted into audio data that has been converted into a signal in the frequency domain and subjected to quantization processing, it is embedded. The inconvenience that the digital watermark information is deleted by the quantization process is eliminated,
An electronic watermark embedding method suitable for digital audio data encoding processing can be provided.

In this embodiment, since the position where the digital watermark is embedded is the position of the frequency component that is important with respect to the human auditory characteristics of each frequency component of the audio data, it has a legitimate right such as copyright. If a third party rewrites this digital watermark information to illegally use the audio data, the decoded sound can easily appear as a change in sound quality or sound quality deterioration, making data tampering effective. Can be suppressed.

That is, in the conventional audio encoding device, the selection of the sub-band is not performed based on the bit allocation information, but the sub-band of the high frequency component is usually selected. However, when the digital watermark information is embedded in this portion, even if the digital watermark is rewritten by a third party, there is no significant effect, and an environment where data is easily falsified is provided. On the other hand, in the present embodiment in which the subband is selected based on the bit allocation information, the above-described inconvenience can be prevented.

In this embodiment, digital watermark information is inserted into data having a further maximum value in a sub-band selected as a frequency component having a high perceptual importance, so that the importance is higher. An electronic watermark can be embedded at the data position, and the change in the sound quality and the deterioration of the sound quality of the sound decoded by rewriting the electronic watermark information can be made more remarkable. When the compression efficiency is not considered so much, the position where the digital watermark is embedded is not limited to the position of the maximum value, but may be the position of the minimum value or any other position.

In the above-described embodiment, R (not shown)
The functions of the above-described embodiment are implemented by the operation of a CPU (or MPU), not shown, according to software programs stored in a recording medium such as an OM.
In this case, the software program itself and means for supplying the program to a computer,
For example, a recording medium storing such a program constitutes the present invention. As a recording medium for storing such a program, in addition to a ROM, for example, a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a CD-RO
M, a magnetic tape, a nonvolatile memory card, or the like can be used.

[0041]

According to the present invention, as described above, digital watermark information is inserted into audio data that has been converted from a time-domain signal into a frequency-domain signal and subjected to quantization processing. Digital watermark information can be prevented from being deleted by the quantization process, and a digital watermark embedding method suitable for digital audio data encoding can be provided.

According to another feature of the present invention, the auditory importance of each frequency component of audio data is obtained, and digital watermark information is inserted into data of frequency components that are important with respect to human auditory characteristics. Therefore, when the digital watermark information is rewritten, the sound quality is likely to be changed or deteriorated when decrypted, and illegal rewriting can be effectively prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an overall configuration of an audio encoding device that is an embodiment embodying a digital watermark embedding device of the present invention.

FIG. 2 is a block diagram illustrating a configuration example of a reversible replacement processing circuit illustrated in FIG. 1;

[Explanation of symbols]

Reference Signs List 1 input terminal of digital audio signal 2 output terminal of encoded data 11 MDCT circuit 12 quantization circuit 13 reversible substitution processing circuit 14 adaptive bit allocation circuit 15 multiplexing circuit 16 digital watermark information 21 first input terminal ( An input terminal for digital watermark information 22 A second input terminal (input terminal for quantized audio data) 23 A third input terminal (input terminal for bit allocation information) 24 A first output terminal (output of replacement position information) 25) Second output terminal (output terminal of replacement value information) 26 Third output terminal (output terminal of audio data subjected to replacement processing) 31 Local maximum value search circuit 32 Subband selection circuit 33 First switch circuit 34 Replacement circuit 35 Second switch circuit

Continued on the front page (51) Int.Cl. ⁶ Identification code FI H03M 7/30 H03M 7/30 A

Claims (15)

[Claims] 1. A digital watermark embedding apparatus, wherein digital watermark information is inserted into audio data that has been converted from a time domain signal into a frequency domain signal and subjected to quantization processing. 2. The digital watermark information is inserted in a process of reversibly replacing the quantized audio data with another data value.
Electronic watermark embedding device according to 1. 3. The electronic watermark according to claim 2, wherein the digital watermark information is additional information transmitted separately when the quantized audio data is reversibly replaced with another data value. Watermark embedding device. 4. A digital watermark for data of a frequency component which is important with respect to human auditory characteristics, further comprising means for determining an auditory importance for each frequency component of the audio data converted to the frequency domain signal. 4. The digital watermark embedding device according to claim 1, wherein information is inserted. 5. The means for determining the perceptual importance of each frequency component of the audio data, wherein a large number of bits are allocated based on bit allocation information for each sub-band obtained by dividing the frequency component of the audio data. 5. The digital watermark embedding device according to claim 4, further comprising a subband selecting unit for selecting a subband, wherein the digital watermark information is inserted into data in the selected subband. 6. The means for determining the auditory importance of each frequency component of the audio data further includes a maximum value detecting means for detecting data having a maximum value in the sub-band selected by the sub-band selecting means. 6. The digital watermark embedding device according to claim 5, wherein the digital watermark information is inserted into the data of the maximum value. 7. A time / frequency conversion unit for converting audio data into a frequency domain using a time / frequency conversion process, and a quantization unit for performing a quantization process on the audio data converted into the frequency domain. An audio encoding device comprising: a digital watermark embedding unit that inserts digital watermark information into the quantized audio data. 8. A reversible replacement means for reversibly replacing the quantized audio data with another data value, the reversible replacement means also serving as the digital watermark embedding means, and The audio encoding apparatus according to claim 7, wherein the digital watermark information is inserted when data is reversibly replaced with another data value. 9. A digital watermark embedding means for obtaining perceptual importance for each frequency component of the audio data converted into the frequency domain signal, wherein the digital watermark embedding means includes a frequency component which is important with respect to human auditory characteristics. 9. The audio encoding apparatus according to claim 7, wherein the digital watermark information is inserted into data. 10. The means for determining perceptual importance for each frequency component of the audio data, wherein a number of bits are allocated based on bit allocation information for each sub-band obtained by dividing the frequency component of the audio data. 10. The audio according to claim 9, further comprising a sub-band selecting unit for selecting a sub-band, wherein the digital watermark embedding unit inserts the digital watermark information into data in the selected sub-band. Encoding device. 11. The means for determining the auditory importance of each frequency component of the audio data further includes a maximum value detecting means for detecting data having a maximum value in the sub-band selected by the sub-band selecting means. 11. The audio encoding apparatus according to claim 10, wherein the digital watermark embedding unit inserts the digital watermark information into the data of the maximum value. 12. The digital watermark information is transmitted separately as additional information of data obtained by reversibly replacing the quantized audio data.
2. The audio data encoding device according to claim 1. 13. For a frequency component whose audio data has been truncated to “0” data by the quantization process, information indicating that the frequency domain is “0” data is transmitted, and 13. The audio encoding apparatus according to claim 7, wherein the digital watermark information is inserted without performing a reversible replacement process. 14. A process for reversibly replacing said quantized audio data with another data value for audio data that has been converted from a time-domain signal to a frequency-domain signal and subjected to quantization processing. A computer-readable recording medium on which a program for causing a computer to function as means for inserting digital watermark information at the time of recording is recorded. 15. A digital watermark for data of a frequency component which is important with respect to human auditory characteristics, comprising: means for determining an auditory importance for each frequency component of the audio data converted into the frequency domain signal. 15. The computer-readable recording medium according to claim 14, wherein a program for causing a computer to further function as a unit for inserting information is recorded.