Bit Replacement Audio Watermarking Using Stereo Signals Term Project Muhammad Umer Kakli Muhammad Naeem TayyabThis Paper was presented in International Conference on New Trends in Information & Service Science 2009 By Wei Cao, Yixin Yan, Shengming Li
Digital Watermarking involves embedding secret dataas an additional information to the digital signal such as Audio, Image or Video Signal. Copyright Protection Video Fingerprinting Broadcast Monitoring
For Digital Audio Watermarking, the approaches can be Blind or Non-blind.For Non-blind watermarking techniques, original signalsare required for watermark extraction while in Blindtechnique original signals are not required to extractwatermark.
Removal Attacks: Trying to remove the watermark signal without attempting to break the security of watermark algorithm. Geometric Attacks: Don’t remove the watermark itself, but intended to distort the watermark detector synchronization with the embedded information. Cryptographic Attacks: Aim at cracking the security methods in watermarking schemes and thus finding a way to remove the embedded watermark information Protocol Attacks: Aim at attacking the entire concept of watermarking application.
LSB Encoding Echo Hiding Spread Spectrum Watermarking Watermarking the phase of the host signal
Watermark added to the Least Significant Bit (LSB) Easy to embed and retrieve High bit rate
De-merits of LSB Encoding Scheme Robustness of this method is very low Watermark bits can be easily detected and changed Addition of High level noise, re-sampling and MP3 Compression may completely destroy the watermark information.Proposed Scheme Instead of using LSB of mono-signal samples, it is perceived that by using higher bits of Stereo-Signal samples, it can be more robust.
The proposed Audio Watermarking scheme improves mono-signal watermarking method by introducing watermarking threshold and making use of Stereo Signals.Mono Signals Vs. Stereo Signals Mono means audio signals are mixed together and routed through a single channel while In Stereo two or more individual channels are using. left channels o/p is connected to the left speakers and right channels o/p is connected to the right speakers. It gives the effect of direction and the depth of sound.
Watermarking threshold is calculated using the following equation Watermarking Threshold = 1/2n-(w+4) n=Number of bits per sample w=Watermark embed bit layer Samples whose values are higher than threshold are considered as “Non-Silent” samples and they are used to embed watermark bits. Samples whose values are lower than threshold are considered as “Silent” samples and they are not used for watermark embedding.
After threshold calculation , let each “non-silent” samplevalue of original stereo signal be represented in 16 bitbinary format. a16,a15,a14,………….a3,a2,a1where a1 is the bit in the 1st bit layer, a2 is the bit in the2nd bit layer and so on.A watermark bit stream is first generated and ith bit layersof “non-silent” samples are used as watermarkembedded bit layer.
If the first bit of the stream is bit “1”, and ai of the first “non-silent”sample of left-channel signal is also bit “1”, no action is taken. If ai isnot “1”, watermark embedding process of left-channel signal isperformed according to the following procedures,
If the first bit of the stream is bit “0”, and ai of the first “non-silent”sample of right-channel signal is also bit “0”, no action is taken. If aiis not “0”, watermark embedding process of right channel signal isperformed according to the following procedures,
Effect of Watermarking on Bit Layers Figure 2: Percentage of Changed bits as embedding in the 5th bit layer
Signal to Noise Ration (SNR) Signal to Noise Embedded Bit Layer of Watermark Signals Ratios (dB) 1st 2nd 3rd 4th 5thStereo Signals 72.09 70.15 67.38 59.36 46.25Mono Signals 66.52 61.49 56.81 44.37 28.53 SNR of Watermarked Stereo and Mono Signals
Robustness under Attack of Addition of NoiseFigure 3: Watermark Extraction Rate Under addition of White noise (for 20dB & 50dB)
Robustness under MP3 Compression Attack Embedded Bit Layer of Watermark Extraction Rate (%) for MP3 Compression Signals 1st 2nd 3rd 4th 5th Extraction Rate (%) 49.80 49.82 49.83 50.06 50.11 Watermark Extraction Rate Under Attack of MP3 Compression
Robustness under Re-Sampling Attack Watermark Embedded Bit Layer of Watermark Signals Extraction Rate (%) 1st 2nd 3rd 4th 5th 14.70 48.99 49.54 49.83 49.71 50.11 Re-sampling Frequency 22.05 49.61 49.73 50.17 50.66 50.70 (KHz) 66.15 49.17 49.84 49.96 50.30 50.43 88.20 50.03 53.29 55.64 58.52 60.79 Watermark Extraction Rate Under Attack of Re-sampling
The noise level due to embedding watermark issignificantly reduced. This schemes is robust againstaddition of white noise, even if the noise level is high.The proposed scheme is not robust against MP3Compression and re-sampling unless frequency isinteger multiple of original sampling frequency.