# US 2014/0156285 A1 · Method and apparatus for quantisation index modulation for watermarking an input signal > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0156285 A1 - Document ID: US20140156285A1 - Status: Published application - Kind: A1 - Application number: 14/131,027 - Filed: 2012-06-25 - Published: 2014-06-05 - Earliest claimed: 2011-07-08 - Assignees: Thomson Licensing - Inventors: Peter Jax - Web page: https://patentgrep.com/patent/US20140156285A1 ## CPC - G10L 19/018: Audio watermarking, i.e. embedding inaudible data in the audio signal - G10L 19/008: Multichannel audio signal coding or decoding using interchannel correlation to reduce redundancy, e.g. joint-stereo, intensity-coding or matrixing - G10L 19/035: Scalar quantisation - G10L 19/24: Variable rate codecs, e.g. for generating different qualities using a scalable representation such as hierarchical encoding or layered encoding - G10L 21/038: using band spreading techniques - G10L: SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING ## Abstract With quantisation index modulation QIM it is possible to achieve a very high data rate, and the capacity of the watermark transmission is mostly independent of the characteristics of the original audio signal, but the audio quality suffers from degradation with each watermark embedding-and-removal step. In order to avoid degradation of the audio quality, the inventive audio signal watermarking uses specific quantiser curves in time domain and in particular in frequency domain for embedding the watermark message into the audio signal, whereby the processing is almost perfectly reversible. Furthermore, it has embedded a power constraint in order to guarantee that the modifications of the audio signal due to the watermark embedding are inaudible. ## Claims ### Claim at position 1 1-11. (canceled) ### Claim 12 Method for quantisation index modulation for watermarking an input signal x, wherein different quantiser curves Qm are used for quantising said input signal x and a current characteristic of said quantiser curve is controlled by the current content of a watermark message m, wherein in said quantising the difference between input value and output value at any position is not greater than T, and that said quantising curves Qm are reversible in that for any input value x there is a unique output value y, wherein ±T is a value defining the y shift towards y=0 of outer sections of said quantiser curves Qm and is determined by the current psycho-acoustic masking level of said input signal x, and y is the watermarked output signal, and wherein the different quantiser curves Qm are established according to the current value of m by different shifts of the complete quantiser curve in x direction. ### Claim 13 (depends on 12) Method according to claim 12, wherein said quantising is carried out according to y=Qm(x)+max(−T, min(T, α(x−Qm(x)))), wherein α is a predetermined steepness of the medium section of said quantiser curves Qm, ±T is a value defining the y shift towards y=0 of the other sections of said quantiser curves Qm and is determined by the current psycho-acoustic masking level of said input signal x, and y is the watermarked output signal. ### Claim 14 (depends on 12) Method according to claim 12, wherein said quantising is carried out in frequency domain. ### Claim 15 (depends on 14) Method according to claim 14, wherein prior to said quantisation said input signal x passes through a time-to-frequency transform and a combining of every successive frame pair, of which one frame is treated as representing a real part of one current frame and the other frame is treated as representing an imaginary part of that current frame, and wherein the quantised input signal passes through a spreading of every successive frame pair, of which one frame is treated as representing a real part of one current frame and the other frame is treated as representing an imaginary part of that current frame, and a frequency-to-time transform, so as to form said watermarked output signal y. ### Claim 16 (depends on 15) Method according to claim 15, wherein said time-to-frequency transform is an MDCT and said frequency-to-time transform is an IMDCT. ### Claim 17 (depends on 12) Method according to claim 12, wherein said output signal y controls phase modifications of said input signal x. ### Claim 18 (depends on 12) Method according to claim 12, wherein said input signal x is an audio signal. ### Claim 19 (depends on 2) Method for regaining an original input signal x which has been processed according to claim 2, said method including the steps: re-quantising according to y=Qm(x)+max(−T, min(T, α(x−Qm(x)))) the received watermarked signal using said quantiser curves Qm in a corresponding manner, wherein different candidate quantiser curves Qm are checked by applying different shifts of the complete quantiser curve in x direction, and wherein said re-quantisation is carried out with a bit depth that is greater than the bit depth that was applied originally; selecting that candidate quantiser curve Qm which matches best in the frequency domain; based on the current Qm so determined, removing the corresponding current watermark m from signal y so as to provide said regained signal x. ### Claim 20 Apparatus for quantisation index modulation for watermarking an input signal x, wherein different quantiser curves Qm are used for quantising said input signal x and a current characteristic of said quantiser curve is controlled by the current content of a watermark message m, said apparatus including: a psycho-acoustic masking level calculator; an embedder which carries out said quantising in which the difference between input value and output value at any position is not greater than T, and wherein said quantising curves Qm are reversible in that for any input value x there is a unique output value y, wherein ±T is a value defining the y shift towards y=0 of outer sections of said quantiser curves Qm and is determined by the current psycho-acoustic masking level of said input signal x, and y is the watermarked output signal, and wherein the different quantiser curves Qm are established according to the current value of m by different shifts of the complete quantiser curve in x direction. ### Claim 21 (depends on 20) Apparatus according to claim 20, wherein said quantising is carried out according to y=Qm(x)+max(−T, min(T, α(x−Qm(x)))), wherein α is a predetermined steepness of the medium section of said quantiser curves Qm, ±T is a value defining the y shift towards y=0 of the other sections of said quantiser curves Qm and is determined by the current psycho-acoustic masking level of said input signal x, and y is the watermarked output signal. ### Claim 22 (depends on 20) Apparatus according to claim 20, wherein said quantising is carried out in frequency domain. ### Claim 23 (depends on 22) Apparatus according to claim 22, comprising: means being arranged prior to said embedder and being adapted for time-to-frequency transform and frame pair combining, wherein of every successive frame pair one frame is treated as representing a real part of one current frame and the other frame is treated as representing an imaginary part of that current frame, means being arranged following said embedder and being adapted for spreading every successive frame pair of which one frame is treated as representing a real part of one current frame and the other frame is treated as representing an imaginary part of that current frame, and for frequency-to-time transform, so as to form said watermarked output signal y. ### Claim 24 (depends on 12) Apparatus according to claim 12, wherein said time-to-frequency transform is an MDCT and said frequency-to-time transform is an IMDCT. ### Claim 25 (depends on 20) Apparatus according to claim 20, wherein said output signal y controls phase modifications of said input signal x. ### Claim 26 (depends on 20) Apparatus according to claim 20, wherein said input signal x is an audio signal. ### Claim 27 (depends on 12) Digital audio or video signal that is encoded according to the method of claim 12. ### Claim 28 (depends on 27) Non-transitory storage medium that contains or stores, or has recorded on it, a digital audio or video signal according to claim 27.