Stealthy audio watermarking

• US 7,266,697 B2
• Filed: 05/03/2004
• Issued: 09/04/2007
• Est. Priority Date: 07/13/1999
• Status: Expired due to Fees

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Kirovski, Darko, Malvar, Henrique
• Primary Examiner(s): REVAK, CHRISTOPHER A
• Application Number:
  US10/838,497
• Publication Number:
  US 20040204943A1
• Time in Patent Office: 1,219 Days
• Field of Search: None
• US Class Current: 713/176
• CPC Class Codes: G10L 19/018 Audio watermarking, i.e. embedding inaudible data in the audio signal
• CPC Class Codes: G11B 20/00086 Circuits for prevention of unauthorised reproduction or copying, e.g. piracy indicating unauthorised use of record carriers in general G11B23/28; scrambling for television signal recording H04N5/913; network architectures or network protocols for network security H04L63/00; cryptographic mechanisms or cryptographic arrangements for secret or secure communication H04L9/00
• CPC Class Codes: G11B 20/00884 involving a watermark, i.e. a barely perceptible transformation of the original data which can nevertheless be recognised by an algorithm
• CPC Class Codes: H04H 20/31 using in-band signals, e.g. subsonic or cue signal
• CPC Class Codes: H04N 2005/91335 the copy protection signal being a watermark

Abstract

Described herein is audio watermarking technology for inserting and detecting watermarks in audio signals, such as a music clip. The watermark identifies the content producer, providing a signature that is embedded in the audio signal and cannot be removed. The watermark is designed to survive all typical kinds of processing and malicious attacks. In one described implementation, a watermarking system employs chess spread-spectrum sequences (i.e., “chess watermarks”) to improve the balance of positive and negative chips in the watermarking sequences. The balance is not imposed in an orderly fashion, which might make the watermark sequence more easily detectable to an attacker, but in a pseudo-random fashion. In that way, better sequence balance is achieved while preserving its randomness for an attacker without knowledge of the keys. In another described implementation, a watermarking system employs an energy-level trigger to determine whether to skip encoding of a portion of a watermark within a given time span of an audio clip. If a large discrepancy in energy levels exists over a given time frame, then the frame is not watermarked, to avoid audible time-dispersion of artifacts due to spectral modifications (which are similar to “pre-echo” effects in audio coding). In another described implementation, a watermarking system begins encoding of a watermark at a variable position after the beginning of an audio clip.

Claims

1. A method for encoding values within a digital audio signal, the method comprising:

receiving the digital audio signal having frequency magnitude components;

analyzing the relative energy levels of the frequency magnitude components of the signal;

determining whether the signal has a large discrepancy in the relative energy levels of the frequency magnitude components, wherein the large discrepancy is a discrepancy of a factor of three or more;

encoding at least one bit of the digital watermark into the digital signal based on the determination.

2. A method as recited in claim 1 further comprising if the signal has no large discrepancy in the relative energy levels of the frequency magnitude components, then encoding at least one value into the signal.

3. A method as recited in claim 1 further comprising if the signal has a large discrepancy in the relative energy levels of the frequency magnitude components, then skipping encoding values into the signal.

4. A computer-readable storage medium having computer-executable instructions that, when executed by a computer, perform a method for encoding values within a digital audio signal, the method comprising;

receiving the digital audio signal having frequency magnitude components;

analyzing the relative energy levels of the frequency magnitude components of the signal;

determining whether the signal has a large discrepancy in the relative energy levels of the frequency magnitude components, wherein the large discrepancy is a discreoancy of a factor of three or more;

encoding at least one bit of the digital watermark into the digital signal based on the determination.

5. A watermark encoding system for encoding bits of a digital watermark within a digital audio signal having frequency magnitude components, the system comprising:

an analyzer to examine the relative energy levels of the frequency magnitude components of the signal and determine whether the signal has a large discrepancy in the relative energy levels of the frequency magnitude components, wherein the large discrepancy is a discrepancy of factor of three or more;

an encoder coupled to the analyzer, the encoder is configured to insert at least one bit of the digital watermark into the digital signal.

6. A system as recited in claim 5, wherein the encoder inserts at least one bit of the digital watermark into the digital signal if the analyzer determines that the signal has no large discrepancy in the relative energy levels of the frequency magnitude components.

7. A system as recited in claim 5, wherein the encoder does not insert a bit of the digital watermark into the digital signal if the analyzer determines that the signal has a large discrepancy in the relative energy levels of the frequency magnitude components.