Data hiding via phase manipulation of audio signals

• US 20050033579A1
• Filed: 06/18/2004
• Published: 02/10/2005
• Est. Priority Date: 06/19/2003
• Status: Active Grant

• Current Assignee: MZ Audio Sciences, LLC
• Original Assignee: University of Rochester
• Inventors: Bocko, Mark F., Ignjatovic, Zeljko
• Granted Patent: US 7,289,961 B2
• Time in Patent Office: Days
• US Class Current: 704/273
• CPC Class Codes: G10L 19/018 Audio watermarking, i.e. embedding inaudible data in the audio signal

Abstract

Data are embedded in an audio signal for watermarking, steganography, or other purposes. The audio signal is divided into time frames. In each time frame, the relative phases of one or more frequency bands are shifted to represent the data to be embedded. In one embodiment, two frequency bands are selected according to a pseudo-random sequence, and their relative phase is shifted. In another embodiment, the phases of one or more overtones relative to the fundamental tone are quantized.

Claims

1. A method for embedding data in an audio signal, the method comprising:

(a) dividing the audio signal into a plurality of time frames and, in each time frame, a plurality of frequency components;

(b) in each of at least some of the plurality of time frames, selecting at least two of the plurality of frequency components; and

(c) altering a phase of at least one of the plurality of frequency components in accordance with the data to be embedded.

2. The method of claim 1, wherein:

step (b) comprises selecting two of the plurality of frequency components in accordance with a pseudo-random sequence; and

step (c) comprises altering a relative phase of the two frequency components in accordance with the data to be embedded.

3. The method of claim 1, wherein:

step (b) comprises selecting a fundamental tone and at least one overtone; and

step (c) comprises quantizing a phase difference of the at least one overtone relative to the fundamental tone to embed at least one bit of the data to be embedded.

4. The method of claim 3, wherein:

step (b) comprises selecting a plurality of said overtones; and

step (c) comprises quantizing the phase differences of the plurality of overtones selected in step (b) to embed a plurality of bits of the data to be embedded.

5. The method of claim 4, wherein step (c) further comprises inverse transforming the plurality of frequency components with the quantized phase differences.

6. The method of claim 1, further comprising (d) reducing a phase discontinuity at boundaries of the time frames caused by step (c).

7. The method of claim 6, wherein step (d) comprises controlling phase shifts introduced in step (c) to go to zero at the boundaries of the time frames.

8. The method of claim 1, wherein the audio signal undergoes lossy compression before steps (a)-(c).

9. The method of claim 1, wherein the audio signal undergoes lossy compression after steps (a)-(c).

10. A method for extracting embedded data from an audio signal, the method comprising:

(a) dividing the audio signal into a plurality of time frames and, in each time frame, a plurality of frequency components;

(b) in each of at least some of the plurality of time frames, selecting at least two of the plurality of frequency components;

(c) determining a phase shift which has been applied to at least one of the plurality of frequency components in accordance with the embedded data; and

(d) from the phase shift determined in step (c), extracting the embedded data.

11. The method of claim 10, wherein step (c) comprises determining which of the plurality of frequency components has the phase shift in accordance with a pseudo-random sequence.

12. The method of claim 10, wherein step (b) comprises selecting a fundamental tone and at least one overtone.

13. The method of claim 12, wherein step (b) comprises selecting the fundamental tone and a plurality of overtones, and wherein step (c) comprises determining the phase shift in each of the plurality of overtones.

14. A device for embedding data in an audio signal, the device comprising:

an input for receiving the audio signal and the data to be embedded;

a processor, in communication with the input, for;

(a) dividing the audio signal into a plurality of time frames and, in each time frame, a plurality of frequency components;

(b) in each of at least some of the plurality of time frames, selecting at least two of the plurality of frequency components; and

(c) altering a phase of at least one of the plurality of frequency components in accordance with the data to be embedded; and

an output, in communication with the processor, for outputting a result of step (c) as the audio signal with the embedded data.

15. The device of claim 14, wherein:

the processor performs step (b) by selecting two of the plurality of frequency components in accordance with a pseudo-random sequence; and

the processor performs step (c) by altering a relative phase of the two frequency components in accordance with the data to be embedded.

16. The device of claim 14, wherein:

the processor performs step (b) by selecting a fundamental tone and at least one overtone; and

the processor performs step (c) by quantizing a phase difference of the at least one overtone relative to the fundamental tone to embed at least one bit of the data to be embedded.

17. The device of claim 16, wherein:

the processor performs step (b) by selecting a plurality of said overtones; and

the processor performs step (c) by quantizing the phase differences of the plurality of overtones selected in step (b) to embed a plurality of bits of the data to be embedded.

18. The device of claim 17, wherein the processor performs step (c) further by inverse transforming the plurality of frequency components with the quantized phase differences.

19. The device of claim 14, wherein the processor further performs (d) reducing a phase discontinuity at boundaries of the time frames caused by step (c).

20. The device of claim 19, wherein the processor performs step (d) by controlling phase shifts introduced in step (c) to go to zero at the boundaries of the time frames.

21. The device of claim 14, wherein the processor performs lossy compression on the audio signal before the processor performs steps (a)-(c).

22. The device of claim 14, wherein the processor performs lossy compression on the audio signal after the processor performs steps (a)-(c).

23. A device for extracting embedded data from an audio signal, the device comprising:

an input for receiving the audio signal;

a processor, in communication with the input, for;

(a) dividing the audio signal into a plurality of time frames and, in each time frame, a plurality of frequency components;

(b) in each of at least some of the plurality of time frames, selecting at least two of the plurality of frequency components;

(c) determining a phase shift which has been applied to at least one of the plurality of frequency components in accordance with the embedded data; and

(d) from the phase shift determined in step (c), extracting the embedded data; and

an output for outputting the embedded data.

24. The device of claim 23, wherein the processor performs step (c) by determining which of the plurality of frequency components has the phase shift in accordance with a pseudo-random sequence.

25. The device of claim 23, wherein the processor performs step (b) by selecting a fundamental tone and at least one overtone.

26. The device of claim 25, wherein the processor performs step (b) by selecting the fundamental tone and a plurality of overtones, and wherein step (c) comprises determining the phase shift in each of the plurality of overtones.

27. An article of manufacture comprising:

a machine-readable storage medium; and

an audio signal recorded on the machine-readable storage medium, wherein the audio signal comprises a plurality of time frames in which frequency components have been phase-shifted to embed data in the audio signal.

28. A signal structure embodied in a carrier wave, the signal structure comprising an audio signal, wherein the audio signal comprises a plurality of time frames in which frequency components have been phase-shifted to embed data in the audio signal.