Thomson Licensing

Other

Peter Georg Baum

Michael Arnold

Ulrich Gries

Walter Voessing

Xiaoming Chen

Jun Tian

Jeffrey Adam Bloom

Ulrich Schreiber

Xiao-Ming Chen

A challenge of audio watermarking systems in which an acoustic path is involved is the robustness against microphone pickup in case of surrounding noise. The strength of phase-based watermarking is increased by determining a masking threshold for a current frequency bin in a frequency/phase representation changing the phase based on that masking threshold and an allowed phase change value, calculating an allowed magnitude change value for the current frequency bin and calculating from an audio quality level value a magnitude change scaling factor for the magnitude change value, and increasing its magnitude accordingly.

Method and apparatus for increasing the strength of phase-based watermarking of an audio signal

Following transmission of a watermarked audio signal over an acoustic path causing echoes, reverberation and/or noise, watermark detection correlation result peak values are concentrated within a limited temporal range around main correlation result peaks, which limited temporal range is much smaller than the total correlation length. The watermark detection is based on the following: given ncorrelation result peak values v=(v, v, . . . , v) in an average or expected probability distribution for correlation result values for unmarked content, the probability is calculated that within windows covering the limited temporal range there are nor more values from a correlation result value set greater than or equal to these peaks v.

Method and apparatus for determining watermark symbols in a received audio signal that can contain echoes, reverberation and/or noise

Audio watermarking is the process of embedding watermark information items into an audio signal in an in-audible manner. In a first embodiment, in case the original audio signal has parts of low signal energy, an alternative signal having a level or strength given by the psycho-acoustic model is combined with the original audio signal. The combined signal is watermarked with watermark data to be embedded. In a second embodiment, in case the original audio signal has parts of low signal energy, an alternative signal having a level or strength given by the psycho-acoustic model is watermarked with watermark data to be embedded, and the audio signal is watermarked with the watermark data to be embedded. The watermarked alternative signal is combined with the watermarked audio signal.

Method and apparatus for watermarking successive sections of an audio signal

For watermark embedding, without full Dolby AC-3 decoding, mantissa bits in the AC-3 bit stream are changed by exploiting the fact that during AC-3 encoding more bits than required by the perceptual masking curve are used for the quantization of the MDCT coefficient mantissa values. In addition to the bap values, truly required bap values are determined and the mantissa values are changed accordingly, controlled by the watermark information. The advantages are efficient watermark embedding, other bit stream parameters and values remain unchanged except for CRC checks, and the audio quality of the watermarked signal remains perceptually unchanged.

Method and apparatus for watermarking an AC-3 encoded bit stream

Digital audio signal watermarking in real-time is difficult in an environment that has limited processing power. According to the invention, the channels in a data block-based audio multi-channel signal are prioritized with respect to watermarking importance, whereby the channel priority can change for different input signal data blocks. For a current input signal block, the most important channel is watermarked and the required processing time is determined. If this required processing time is shorter than a predefined application-dependent threshold, the next most important channel is marked and the additionally required processing time is determined, and so on. Due to the block-based nature of the audio watermarking including block overlap/add and due to the sensitivity of the resulting audio quality against blocking artifacts, several problems are solved in order to lead to acceptable performance and quality.

Method and apparatus for frequency domain watermark processing a multi-channel audio signal in real-time

Watermark symbol detection requires a detection metric for deciding at decoder side which candidate symbol is embedded inside the audio or video signal content. The invention provides an improved detection metric processing that achieves a reliable detection of watermarks in the presence of additional noise and echoes, and that is adaptive to signal reception conditions and requires a decreased computational power. This is performed by taking into account the information contained in the echoes of the received audio signal in the decision metric and comparing it with the corresponding metric obtained from decoding a non-marked audio signal, based on recursive calculation of false positive detection rates of peaks in correlation result values. The watermark symbol corresponding to the reference sequence having the lowest false positive error is selected as the embedded one.

Method and apparatus for detecting which one of symbols of watermark data is embedded in a received signal

In watermarked signal decoding, the embedded message is decoded by correlating the reference patterns with the watermarked signal. The watermark detector decides, depending on the size of the correlation result values, whether or not a given reference pattern was embedded. However, decoding watermarked audio or video signals is difficult if the link between the watermark encoder and the watermark decoder is not a digital one, for example an acoustic path. A re-sampler control unit controls the sampling frequency of a re-sampler, in connection with a watermark decoder that outputs, in addition to the watermark information bits, a corresponding confidence value that is derived from the correlation result and that is used for synchronizing the re-sampler sampling frequency with the original sampling frequency of the watermarked signal. The synchronization processing includes a search mode and a synchronized mode.

Method and apparatus for determining and using the sampling frequency for decoding watermark information embedded in a received signal sampled with an original sampling frequency at encoder side

A method and apparatus are described for determining a threshold, including selecting a desired false result probability, and selecting a threshold value from a threshold table corresponding to the desired false result probability. Also described are a method and apparatus for determining a threshold corresponding to a desired false result probability, including calculating a false result probability, calculating a difference value between the calculated false result probability and the desired false result probability, comparing the difference value to a first predetermined value and comparing the difference value to a second predetermined value if a result of the first comparing act is positive.

Method and apparatus for setting a detection threshold given a desired false probability

Many watermarking systems make use of correlation for calculating a detection metric, which means that several reference patterns are generated at encoder side and one or more of them are embedded inside the content signal, dependent on the message to be embedded. To decode the embedded message, it is necessary to discover which reference pattern was embedded at encoder side by correlating the known reference patterns with the content signal. In the case where watermarked audio is emitted by a loudspeaker and then captured with a microphone, the received signal echoes are used for watermark detection instead of treating them as noise by integrating the correlation values resulting from echoes into the main correlation peak, thereby using correlation result amplitude values located within a predetermined neighborhood of a correlation result peak amplitude value and exceeding a predetermined threshold.

Method and apparatus for determining whether or not a reference pattern is present in a received and possibly watermarked signal

Watermarking of audio signals intends to manipulate the audio signal in a way that the changes in the audio content cannot be recognized by the human auditory system. The watermark data are decoded from the received watermarked audio signal by correlation with corresponding candidate reference sequences. One or more of the sync symbols are embedded twice in the watermark data frame in the encoder. Thereafter a circular correlation is calculated instead of a standard correlation.

Method and apparatus for correlating two data sections

Every watermarking processing needs a detection metric to decide at decoder side whether audio signal content is marked, and which symbol is embedded inside the audio signal content. The invention provides a new detection metric that achieves a reliable detection of watermarks in the presence of additional noise and echoes. This is performed by taking into account the information contained in the echoes of the received audio signal in the decision metric and comparing it with the corresponding metric obtained from decoding a non-marked audio signal, based on calculating the false positive detection rates of the reference sequences for multiple peaks. The watermark symbol corresponding to the reference sequence having the lowest false positive error is selected as the embedded one.

Method and apparatus for regaining watermark data that were embedded in an original signal by modifying sections of said original signal in relation to at least two different reference data sequences

Watermark information (denoted WM) consists of several symbols which are embedded continuously by reference sequence modulation in an audio or a video signal. At decoder site the WM is regained using correlation of the received signal with a corresponding reference sequence. The symbols form watermark data frames. The invention uses for the bit values 'zero' and 'one' in each payload symbol and for each payload symbol in a watermark data frame different reference sequences, without using synchronisation symbols. A logarithmic search is performed in the WM decoder to reduce the numbers of correlations to be calculated. The invention makes watermarking of critical sound signals much more robust.

Method and apparatus for encoding/decoding symbols carrying payload data for watermarking of an audio or video signal

Watermarking of audio signals intends to manipulate the audio signal in a way that the changes in the audio content cannot be recognised by the human auditory system. In order to reduce the audibility of the watermark and to improve the robustness of the watermarking the invention uses phase modification of the audio signal. In the frequency domain, the phase of the audio signal is manipulated by the phase of a reference phase sequence, followed by transform into time domain. Because a change of the audio signal phase over the whole frequency range can be audible, the phase manipulation is carried out with a maximum amount only within one or more small frequency ranges which are located in the higher frequencies and/or in noisy audio signal sections, according to psycho-acoustic principles. Preferably, the allowable amplitude of the phase changes in the remaining frequency ranges is controlled according to psycho-acoustic principles. The watermark is decoded from the watermarked audio signal by correlating it with corresponding inversely transformed candidate reference phase sequences.

Blind watermarking of audio signals by using phase modifications

Watermark information consists of several data symbols which are embedded continuously in an audio or a video signal using modulation with a pseudo-random sequence if spread spectrum technology is used. At decoder site the watermark information is regained using correlation of the received signal with a candidate pseudo-random sequence. Such correlation can be performed by one-dimensional real-symmetric fast Fourier transform of the two input signal vectors, which each consist of a section of N values of the input signal, to which section N&#x2212;1 zeroes are attached, by multiplying one of the transformed vectors by the conjugated version of the other transformed vector, followed by inverse RFFT transform of that frequency domain product vector. However, if the level of a spread-spectrum watermark is too low or if too much noise had been added during the transmission of the audio or video signals, the correlation does not show a clear peak, which means that the watermark information bits cannot be recovered. According to the invention, the correlation result is improved by setting to zero in the frequency domain frequency bins of the vector which do not have a positive impact on the correlation peak at location zero, i.e. which frequency bins do not contribute to that peak. Thereby the noise level in the correlation or matched filter output is reduced and the watermark information items can be recovered or decoded correctly from the received watermarked audio or video signal.

Decoding watermark information items of a watermarked audio or video signal using correlation

Spread spectrum technology is used for watermarking digital audio signals. To retrieve a watermark signal information bit from the spread spectrum at the receiver or decoder side, the received or replayed spectrum is convolved with a spreading function that is time-inverse with respect to the original spreading function. The pseudo noise sequences are modulated on carrier frequencies which are inserted at one or more frequency bands into the spectrum of an audio signal. The watermark signal decoder checks the frequency bands occupied by such carriers. The frequency band occupation information is signaled in advance, i.e. is transmitted already together with the frame data for the current frame, such that the watermark signal decoder knows before processing the following audio signal frame which carrier frequencies are occupied and must be used for the corresponding carrier demodulation, and which carrier frequencies need not be checked and demodulated.

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Hannover, Germany

Peter Georg Baum