Thomson Licensing

Deutsche Thomson-brandt Gmbh

Thomson Licensing S.a.

Telefunken Fernseh Und Rundfunk Gmbh

Walter Voessing

Peter Georg Baum

Ernst F Schroder

Ulrich Gries

Michael Arnold

Hartmut Peters

Otto Klank

Werner Scholz

Paul-Louis Meunier

Hans-Joachim Platte

Andreas Aust

Friedrich Timmermann

Max Artigalas

Wulf-Christian Streckenbach

Gunter Oberjatzas

Fei Gao

Ernst F Schroeder

Bernd Wessolly

Werner Bachnick

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

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

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.

Method and apparatus for transmitting watermark data bits using a spread spectrum, and for regaining watermark data bits embedded in a spread spectrum

Watermark information (denoted WM) consists of several symbols which are embedded continuously in an audio or a video signal. At decoder site the WM is regained using correlation of the received signal with an m-sequence if Spread Spectrum is used. According to the invention, each WM symbol carries an identification data ID item in addition to its normal payload, and it is already tested in the encoder whether or not the signal is good enough so that the embedded symbol can be recovered at decoder side. If true, it is embedded. If not true, no WM is embedded for the length of one symbol and the test is repeated for the following symbol. The sequence of IDs is known at the encoder which can therefore detect using the ID whether or not a symbol has been skipped.

Method and apparatus for encoding symbols carrying payload data for watermarking an audio or video signal, and method and apparatus for decoding symbols carrying payload data of a watermarked audio or video signal

MPEG 1 Audio data compression is based on subband coding. A quantization is performed using a psychoacoustic model which is adapted to the masking behavior of the human hearing. Each subband signal is quantized in such a way that the quantization noise introduced by the coding will not exceed the masking curve for that subband. In ISO/IEC 11172-3 two independent psychoacoustic models are defined. The output from these psychoacoustic models is a set of Signal-to-Masking Ratios, SMR, for every subband n. In order to calculate the SMRfor the psychoacoustic model 2 according to the invention a Fast Fourier Transformation is performed with a length of L=1152 samples by calculating k subtransformations over 2samples with k*2=L and fitting together the results of the k subtransformations.

Method and encoder for bit-rate saving encoding of audio signals

A magnetic tape apparatus for the recording and reproduction of signals, including a magnetic tape having plural data tracks running parallel to an edge of the tape; a multi-track reading device including a multi-track playback head configured to read simultaneously plural of the tracks and output signals corresponding to data recorded on the plural tracks; and a housing in which the tape and the reading device are permanently disposed; wherein the tape is adapted for simultaneous recording of data onto plural data tracks of the tape via external recording heads upon the apparatus being connected to an external recording facility.

Magnetic tape apparatus with housing in which playback electronics and

A method of digital transmission of an audio signal, in which in order to save transmission and/or memory capacity, the digital signal is converted, before transmission, into signals representing the short-term spectrum of time sections of the digital signal and portions of this signal are processed on the basis of psycho-acoustic laws, with portions of this signal lying below given thresholds left unconsidered, with at least one first threshold being defined below which only amplitude values outside of psycho-acoustically differentiable frequency ranges are left unconsidered.

Method of transmitting an audio signal

A system for transmitting and receiving digitalized audio signals, particularly via satellites, wherein data sequences are arranged in timely succession within frames, wherein before transmission, the digitalized audio signal is converted to a digital signal representing the momentary frequency spectrum and, during subsequent coding of the digital audio signal to be transmitted, portions of this transformed signal are given different weights on the basis of psychoacoustic laws with respect to the accuracy of their representation.

Transmission system

A pulse code modulated audio signal transmission system which compensates for signal interference in the pulse code modulated audio signal. The system includes a first device for receiving an audio signal and for converting the audio signal into a pulse code modulated audio signal, and a second device for receiving the audio signal and for producing an auxiliary signal corresponding to the audio signal but having a smaller bandwidth than the audio signal. A transmission circuit is connected to the first and second devices for receiving the pulse code modulated audio signal and the auxiliary signal and for producing an output signal which comprises the audio signal with portions of the audio signal which contain interference being substituted with corresponding portions of the auxiliary signal.

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Hannover, Germany

Walter Voessing