Method and apparatus for increasing the strength of phase-based watermarking of an audio signal

Patent metadata

Field	Value
Publication number	US-2016379653-A1
Application number	US-201615191855-A
Country	US
Kind code	A1
Filing date	Jun 24, 2016
Priority date	Jun 26, 2015
Publication date	Dec 29, 2016
Grant date	—

Abstract

A challenge of audio watermarking systems in which an acoustic path is involved is the robustness against microphone pickup in case of surrounding noise. The strength of phase-based watermarking is increased by determining a masking threshold for a current frequency bin in a frequency/phase representation changing the phase based on that masking threshold and an allowed phase change value, calculating an allowed magnitude change value for the current frequency bin and calculating from an audio quality level value a magnitude change scaling factor for the magnitude change value, and increasing its magnitude accordingly.

First claim

What is claimed is:

1 . A method for increasing the strength of phase-based watermarking of an audio signal, which watermarked audio signal is suitable for acoustic reception and watermark detection in the presence of surrounding noise, said method including:
determining a masking threshold for a phase change based watermarking of a current frequency bin in a frequency/phase representation of said audio signal, wherein said masking threshold determination is controlled by a given audio quality level value representing the audio quality following said audio signal watermarking; determining an allowed phase change value for the phase of said current frequency bin, according to a reference angle to be embedded in that current frequency bin, which reference angle is derived from a watermark pattern; changing the phase of said current frequency bin according to said allowed phase change value; based on said masking threshold and said allowed phase change value, calculating an allowed magnitude change value for said current frequency bin, and calculating from the audio quality level value a magnitude change scaling factor; calculating a scaled allowed magnitude change values from said allowed magnitude change value and said scaling factor; increasing the magnitude of said current frequency bin by said scaled allowed magnitude change values, so as to output said current frequency bin with said changed phase and said increased magnitude.

2 . An apparatus for increasing the strength of phase-based watermarking of an audio signal, which watermarked audio signal is suitable for acoustic reception and watermark detection in the presence of surrounding noise, said apparatus including means adapted to:
determining a masking threshold for a phase change based watermarking of a current frequency bin in a frequency/phase representation of said audio signal, wherein said masking threshold determination is controlled by a given audio quality level value representing the audio quality following said audio signal watermarking; determining an allowed phase change value for the phase of said current frequency bin, according to a reference angle to be embedded in that current frequency bin, which reference angle is derived from a watermark pattern; changing the phase of said current frequency bin according to said allowed phase change value; based on said masking threshold and said allowed phase change value, calculating an allowed magnitude change value for said current frequency bin, and calculating from the audio quality level value a magnitude change scaling factor; calculating a scaled allowed magnitude change values from said allowed magnitude change value and said scaling factor; increasing the magnitude of said current frequency bin by said scaled allowed magnitude change values, so as to output said current frequency bin with said changed phase and said increased magnitude.

3 . The method according to claim 1 , wherein no phase changes are carried out for frequency bins representing a frequency smaller than a first frequency threshold value and for frequency bins representing a frequency greater than a second frequency threshold value that is greater than said first frequency threshold value.

4 . The method according to claim 1 , wherein a magnitude change value for said current frequency bin is denoted δX[i] and
δ X[i ]=√{square root over ( LT g [i] 2 −X[i] 2 +( X[i ] cos(δφ[ i ])) 2 )}− X[i]+X[i ] cos(δφ[ i ]),

where LT g [i] is said current masking threshold, X[i] is the original magnitude of said current frequency bin, and δφ[i] is said current phase change value.

5 . The method according to claim 1 , wherein said magnitude change scaling factor is denoted f and f=10 −maskingCurveOffset/20 ,
where

maskingCurveOffset
=

100
-
level

100

×

30


[
dB
]

 and level has a value between ‘0’ and ‘100’ and is said audio quality level value, with level=100 for the the best audio quality.

6 . A storage medium, for example an optical disc or a prerecorded memory, that contains or stores, or has recorded on it, a digital audio signal encoded according to the method of claim 1 .

7 . A computer program product comprising instructions which, when carried out on a computer, perform the method according to claim 1 .

8 . The apparatus according to claim 2 , wherein no phase changes are carried out for frequency bins representing a frequency smaller than a first frequency threshold value and for frequency bins representing a frequency greater than a second frequency threshold value that is greater than said first frequency threshold value.

9 . The apparatus according to claim 2 , wherein a magnitude change value for said current frequency bin is denoted δX[i] and
δ X[i ]=√{square root over ( LT g [i] 2 −X[i] 2 +( X[i ] cos(δφ[ i ])) 2 )}− X[i]+X[i ] cos(δφ[ i ]),

where LT g [i] is said current masking threshold, X[i] is the original magnitude of said current frequency bin, and δφ[i] is said current phase change value.

10 . The apparatus according to claim 2 , wherein said magnitude change scaling factor is denoted f and f=10 −maskingCurveOffset/20 ,
where

maskingCurveOffset
=

100
-
level

100

×

30


[
dB
]

 and level has a value between ‘0’ and ‘100’ and is said audio quality level value, with level=100 for the best audio quality.

Assignees

• Thomson Licensing

Inventors

• Arnold Michael
• Baum Peter Georg
• Chen Xiaoming
• Gries Ulrich

Classifications

• G10L19/0204

  using subband decomposition · CPC title

• G10L19/018 Primary

  Audio watermarking, i.e. embedding inaudible data in the audio signal · CPC title