Audio watermarking

• US 20060047517A1
• Filed: 09/01/2005
• Published: 03/02/2006
• Est. Priority Date: 09/01/2004
• Status: Abandoned Application

• Current Assignee: Adam Skeaping
• Original Assignee: Adam Skeaping
• Inventors: Skeaping, Adam
• Application Number:
  US11/217,534
• Publication Number:
  US 20060047517A1
• 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
• 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 20/00891 embedded in audio data

Abstract

A method of watermarking audio tracks and a method of detection of such watermarks. A watermark is applied to an audio track by inverting the audio signal between two points on the audio track. Inversion of an audio signal results in no perceivable change in the audio characteristics of the audio track. The start and end points of the inverted portion are preferably selected to be at zero-crossing points of the audio waveform and at parts of the audio track which comprise high frequency energy so as to disguise these points. The watermark is detected by synchronising an original non-watermarked audio track with a watermarked audio track. When played back together there should preferably be complete cancellation of the signals for the duration of the inverted portion and at least degradation of the sound quality.

Claims

1. A method of generating a watermarked audio track comprising the steps of:

inverting the audio signal waveform at one or more locations on an original audio track thereby generating said watermark audio track, wherein said inverted audio signal is said watermark.

2. The method of claim 1 wherein the start and points of said one or more locations are chosen to be at a zero crossing point of the audio signal waveform.

3. The method of claim 1 wherein the start and end points of said one or more locations are chosen to be at a part of the audio track which comprises high frequency energy.

4. The method of claim 1 wherein the start and end points of said one or more locations are chosen to be at a part of the audio track which comprises an irregular waveform.

5. The method of claim 1 wherein said watermarked audio track is generated on a recording medium.

6. The method of claim 1 wherein said audio track is an analog audio track.

7. The method of any of claim 1 wherein said audio track is a digital audio track.

8. The method of claim 7 wherein said recording medium is a compact disc.

9. The method of claim 1 wherein inverted signal portion comprises a plurality of cycles of the audio signal waveform.

10. The method of any of claim 1 wherein the inverted signal portion is a least one second long.

11. The method of claim 10 wherein said inverted signal portion is at least two minutes long.

12. The method of claim 1 wherein the positions of the start and end points of said one or more locations are logged to an accuracy of 1/25^th of a second.

13. The method of claim 12 wherein the positions of the start and end points of said one or more locations are logged to an accuracy of 1/75^th of a second.

14. A recording medium, having stored thereon a watermarked audio track, the watermarked audio track comprising:

an audio signal, wherein the audio signal waveform is inverted, with reference to an original audio signal at one or more locations of said original audio track, the inverted audio signal portions being said watermark.

15. The recording medium of claim 14 wherein said audio track is an analog audio track.

16. The recording medium of claim 14 wherein said audio track is a digital audio track.

17. The recording medium of claim 16 wherein said recording medium is a compact disc.

18. A method of establishing whether or not an audio track contains a watermark using an original un-watermarked audio track, in which an original watermarked audio track comprises an audio signal, wherein the audio signal waveform is inverted, with reference to an original audio signal, at one or more locations of said original audio track, the inverted audio signal portions being said watermark, the method comprising the steps of:

synchronising said original un-watermarked audio track with a suspect audio track; and

playing said synchronised audio tracks together;

wherein at said one or more locations detecting a change in a first characteristic of the suspect audio track is a watermarked audio track.

19. The method of claim 18 wherein said tracks are synchronised at the start and end points of said one or more locations.