System and method of retrieving a watermark within a signal

• US 7,802,101 B2
• Filed: 03/30/2009
• Issued: 09/21/2010
• Est. Priority Date: 06/04/2001
• Status: Expired due to Fees

• Current Assignee: AT&T Intellectual Property I LP (AT&T, Inc.)
• Original Assignee: AT&T Intellectual Property I LP (AT&T, Inc.)
• Inventors: Johnston, James David, Kuo, Shyh-Shiaw, Turin, William, Quackenbush, Schuyler Reynier
• Primary Examiner(s): Shiferaw; Eleni A
• Application Number:
  US12/414,602
• Publication Number:
  US 20090185692A1
• Time in Patent Office: 540 Days
• Field of Search: 713/176, 380/28, 380/283, 380/282, 380/252, 380/200, 380/216, 380/218, 380/221, 380/237, 380/250, 283/113, 358/3.28, 382/100, 704/203, 704/500
• US Class Current: 713/176
• CPC Class Codes: G10L 19/018 Audio watermarking, i.e. embedding inaudible data in the audio signal

Abstract

A system and method of retrieving a watermark in a watermarked signal are disclosed. The watermarked signal comprises odd and even overlapped blocks where the watermark is contained in the even blocks. The method comprises, for each k-th even block, subtracting the two adjacent odd numbered blocks from the k-th even block of the watermarked signal to retrieve s *_k(n), transforming s *_k(n) into the frequency domain to generate S _k(f), calculating a phase of S _k(f) as φ (f) and a phase of S_k(f) as φ(f), calculating the difference Ψ (f) between φ (f) and φ(f), unwrapping Ψ (f) to obtain the phase modulation {tilde over (Φ)} _k(f), and using a Viterbi search to retrieve the watermark embedded in {tilde over (Φ)} _k(f).

Claims

1. A computer-implemented method for retrieving a watermark in a watermarked signal, the method comprising:

determining via a processor whether a result of adding a phase-modulation to the phase of an original signal has an absolute value greater than value x during a phase-modulation stage of generating the watermarked signal;

if yes, then unwrapping Ψ

(f) to obtain a phase modulation {tilde over (Φ

)} _k(f) only when φ

(f) >

π

/2 and Ψ

(f) is greater than a dynamic range of the phase modulation; and

using a Viterbi search to retrieve the watermark.

2. The computer implemented method of claim 1, further comprising:

subtracting odd blocks from k-th block of the watermarked signal to generate a first signal.

3. The method of claim 2, further comprising:

applying a Fast Fourier Transform (FFT) to the first signal to generate a phase S _k(f).

4. The method of claim 3, further comprising:

calculating a phase of S _k(f) as φ

(f) and a phase of an original signal S_k(f) as φ

(f).

5. The method of claim 4, further comprising:

calculating the difference Ψ

(f) between φ

(f) and φ

(f).

6. The method of claim 1, wherein the watermarked signal is an audio signal.

7. A computing device for retrieving a watermark in a watermarked signal, the computing device comprising:

a processor;

a first module configured to control the processor to determine whether a result of adding a phase-modulation to the phase of the original signal has an absolute value greater than a value x during a phase-modulation stage of generating a watermarked signal;

a second module configured to control the processor, if yes, to unwrap Ψ

(f) to obtain a correct phase modulation Φ

_k(f) only when φ

(f)>

π

/2 and Ψ

(f) is greater than a dynamic range of the phase modulation; and

a third module configure to control the processor to use the Viterbi search to retrieve the watermark.

8. The computing device of claim 7, further comprising:

a fourth module configured to control the processor to subtract odd blocks from k-th block of the watermarked signal to generate a first signal.

9. The computing device of claim 8, further comprising:

a fifth module configured to control the processor to apply a Fast Fourier Transform (FFT) to the first signal to generate a phase S _k(f).

10. The computing device of claim 9, further comprising:

a sixth module configured to control the processor to calculate a phase of S _k(f) as φ

(f) and a phase of an original signal S_k(f) as φ

(f).

11. The computing device of claim 10, further comprising:

a seventh module configured to control the processor to calculate the difference Ψ

(f) between φ

(f) and φ

(f).

12. The computing device of claim 7, wherein the watermarked signal is an audio signal.

13. A tangible computer-readable storage medium storing instructions for controlling the compute device to perform the steps to retrieve a watermark in a watermarked signal, the steps comprising:

determining via a processor whether a result of adding a phase-modulation to the phase of an original signal has an absolute value greater than value x during a phase-modulation stage of generating the watermarked signal;

if yes, then unwrapping Ψ

(f)to obtain a phase modulation {tilde over (Φ

)} _k(f) only when φ

(f)>

π

/2and Ψ

(f) is greater than a dynamic range of the phase modulation; and

using a Viterbi search to retrieve the watermark.

14. The tangible computer-readable storage medium of claim 13, wherein the steps further comprise:

subtracting odd blocks from k-th block of the watermarked signal to generate a first signal.

15. The tangible computer-readable storage medium of claim 14, wherein the steps further comprise:

applying a Fast Fourier Transform (FFT) to the first signal to generate a phase S _k(f).

16. The tangible computer-readable storage medium of claim 15, wherein the steps further comprise:

calculating a phase of S _k(f) as φ

(f) and a phase of an original signal S_k(f) as φ

(f).

17. The tangible computer-readable storage medium of claim 16, wherein the steps further comprise:

calculating the difference Ψ

(f) between φ

(f) and φ

(f).

18. The tangible computer-readable storage medium of claim 13, wherein the watermarked signal is an audio signal.

19. The tangible computer-readable storage medium of claim 14, wherein odd blocks substracted from the k-th even block are the two adjacent odd blocks of the original signal to the k-th even block.