The Audio watermarking

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Information about The Audio watermarking

Published on February 1, 2014

Author: ProfSaxena



Audio watermarking now becomes need if we want to protect our audio contents from an unauthorized copying and distribution over internet.


Digital audio watermarking is a technique for embedding additional data(for example image) along with audio signal so that it will not effect its perceptual quality of an audio signal Embedded data is used for copyright owner identification . the watermark (for example image , data, random sequence)should be robust against various signal processing attacks Audio watermarking is a technique used to hide certain copyright information (for example image, data, random sequence etc) with audio signal in such a way that This is not be hearable to human ear and it should robust against all kind of intentional and non intentional attacks , and can be used for the purpose of Intellectual Property Rights.

In the process of watermarking there are two signals [1] Host signal (for example audio, video, image, text) which is to be protected from unauthorized distribution. [2]Watermark: may be a binary data sequence or an image which is to be embedded as a proof of ownership with host signal. “Watermarking is the process of embedding information into a signal (e.g audio, video or pictures) in a way that is difficult to remove. If the signal is copied, then the information is also carried in the copy.”

NEED OF WATERMARKING With the growth of the Internet, unauthorized copying and distribution of digital media has never been easier. As a result, the music industry claims a multibillion dollar annual revenue loss due to piracy, Normally an application is developed by a person or a small group of people and used by many. Hackers are the people who tend to change the original application by modifying it or use the same application to make profits without giving credit to the owner. So we do require a technique which can protect our data from unauthorized copying and distribution and can provide copyright owner identification For our digital data over internet.

OTHER TECHNIQUE WHICH CAN PROTACT UNAUTHORIZED ACCESS OF DATA  1. STNEOGRAPHY steganography is a technique to send information by writing on the cover object invisibly. Steganography comes from the Greek word that means covered writing (Stego = covered and Graphy = writing). Here the authorized party is only aware of the existence of the hidden message.  2. CRYPTOGRAPHY In cryptographic techniques significant information is encrypted so that only the key holder has access to that information, once the information is decrypted the security is lost. Cryptography protects the contents of the message.

DIFFERENCES BETWEEN STEGANOGRAPHY AND WATERMARKING Although steganography and watermarking both describe techniques used for covert communication, steganography typically relates only to covert point to point communication between two parties. The main purpose of steganography is to hide the fact of communication. The sender embeds a secret message into digital media (e.g. image) where only the receiver can extract this message Steganographic methods are not robust against attacks or modification of data that might occur during transmission, storage or format conversion Watermarking is techniques whose primary objective is the security of the object rather than the invisibility of the object. The significant difference between the two techniques is the superior robustness capability of watermarking schemes.

DIFFERENCE BETWEEN CRYPTOGRAPHY AND WATERMARKING:IN Cryptography technique message is encrypted and only intented receiver(Key holder) can decrypt the message . It is mainly useful for point to point communication.In cryptography once message is decrypted then security lost. In watermarking technique message is not encrypted but an another secreat information is inserted with host signal in such a way that it will not effect Its perceptual quality and can be used as Copyright.

APPLICATIONS OF WATERMARKING Ownership protection and proof of ownership: Authentication and tampering detection Copy control and access control Information carrier Finger printing Broadcast monitoring Medical applications Airline traffic monitoring

REQUIREMENTS OF WATERMARKING According to IFPI (International Federation of the Phonographic Industry) audio watermarking algorithms should meet certain requirements. The most significant requirements are perceptibility,roubstness,security, reliability, capacity, and speed performance. [1]PERCEPTIBILITY:One of the important features of the watermarking technique is that the watermarked signal should not lose the quality of the original signal. The signal to noise ratio (SNR) of the watermarked signal to the original signal should be maintained greater than 20dB . In addition, the technique should make the modified signal not perceivable by human ear. [2]ROUBSTNESS TO SIGNAL PROCESSING ATTACKS: Watermark should be roubst against common signal processing attacks such as lossy compression ,linear filtering,Resampling,Requantization,cropping, jittering, D/A and A/D conversion, Normal correlation (N.C.)is used for the measurement of roubstness. [3] CAPACITY: The efficient watermarking technique should be able to carry more information but should not degrade the quality of the audio signal.

REQUIREMENTS OF WATERMARKING [4]SPEED: Speed of embedding is one of the criteria for efficient watermarking technique. The speed of embedding of watermark is important in real time applications where the embedding is done on continuous signals such as, speech of an official or conversation between airplane pilot and ground control staff. Security and Cost [5]COMPUTATIONAL COMPLEXITY:Computational complexity refers to the processing required to embed watermark data into a host signal, and /or to extract the data from the signal.

TRADE OFF BETWEEN THE VARIOUS REQUIREMENT OF WATERMARKING The Imperceptibility, Roubustness and Capacity are the three most important characteristics of a watermarking algorithm. However, there is a trade-off between these three characteristics As seen from Figure imperceptibility, robustness and capacity are conflicting characteristics of a watermarking system . ie at the same time one can not fullfill all the requirement of watermarking simultaneously.

PROBLEMS AND ATTACKS ON WATERMARKING COMPRESSION: To reduce the size of watermarked audio signal Is called compression. RESAMPLING: During Analog to digital conversion a signal can be Resampled at different different sampling frequencies. REQUANTIZATION: A signal can be Requantized with different quantization Level as we change the quantization level the quantization error also changed And no of bits used to represent per sample also changed. FILTERING:filtering is used to filter certain frequency componants of any signal or we can say that it attenuate certain frequency componant of any signal. ADDITIVE WHITE GAUSSION NOISE ATTACKS :A.W.G.N. can be added to watermark signal during attack. CROPPING: Cropping means to remove the certain part from the watermarked signal.

THE HUMEN AUDIORATORY SYSTEM [H.A.S.] Watermarking of audio signals is more challenging compared to the watermarking of images or video , due to wider dynamic range of the HAS in comparison with human visual system (HVS) . The HAS perceives sounds over a range of power greater than 109:1 and a range of frequencies greater than 103:1. The sensitivity of the HAS to the additive white Gaussian noise (AWGN) is high as well noise in a sound file can be detected as low as 70 dB below ambient level.

Most audio watermarking schemes rely on the imperfections of the human auditory system (HAS). HAS is insensitive to small amplitude changes in the time and frequency domains, allowing the addition of weak noise signals (watermarks) to the host audio signal such that the changes are inaudible. In the time domain, it has been demonstrated that the HAS is insensitive to small level changes and insertion of low-amplitude echoes [3]. Data hiding in the frequency domain takes advantage of the insensitivity of the HAS to small spectral magnitude changes [3]. Further, HAS is insensitive to a constant relative phase shift in a stationary audio signal and some spectral distortions are interpreted as natural, perceptually non-annoying ones [39].

Two Properties of the HAS dominantly used in watermarking algorithms are 1. frequency (simultaneous) masking 2.temporal masking FREQUENCY(SIMULTANEOUS) MASKING: Frequency (simultaneous) masking is a frequency domain observable fact where low levels signal (the maskee) can be made inaudible (masked) by a simultaneously appearing stronger signal (the masker), if the masker and maskee are close enough to each other in frequency [5]. TEMPORAL MASKING: .In the time domain, it has been demonstrated that the HAS is insensitive to small level changes and insertion of low-amplitude echoes [3]. Frequency domain techniques, in particular, have been more effective than time-domain techniques since watermarks are added to selected regions in the transformed domain of the host audio signal, such that inaudibility an robustness are maintained [18]


Further the wathermarking can be done in time domain as well as in frequency domain The commenly used time domain algorithms are LSB Coding, Echo hiding, patchwork algorithms etc Whereas frequency domain algorithms are Phase coding Cofficient quantization Embedding the watermark by modifying the cofficients of the transform outputs such as F.F.T. (Fast Fourier Transform) , S.T.F.T. (Sort time fourier Transform), D.C.T. (Discrete fourier transform), D.W.T. (Discreat wavelet transform) etc.

LSB CODING This technique is one of the common techniques employed in signal processing applications. It is based on the substitution of the LSB of the carrier signal with the bit pattern from the watermark noise. The robustness depends on the number of bits that are being replaced in the host signal. Fig L.S.B. CODING

ECHO WATERMARKING Echo hiding schemes embed watermarks into a host signal by adding echoes to produce watermarked signal. The nature of the echo is to add resonance to the host audio. After the echo has been added, watermarked signal retains the same statistical and perceptual characteristics. The offset (or delay) between the original and a watermarked signal is small enough that the echo is perceived by the HAS as an added resonance.

PATCHWORK TECHNIQUE The data to be watermarked is divided into two distinct subsets. One feature of the data is selected and customized in opposite directions in both subsets . For an example let the original signal is divided into two parts A and B, then the part A is increased by a fraction Δ and the part B is decreased by some amount Δ. The samples separation is the secret key which is termed as watermarking key. Let NA and NB indicate the size(s) of the individual A and B parts and Δ be the total of the change made to the host signal. Suppose that a[i] and b[i] represent the sample values at ith position in blocks A and B. The difference of the sample values can be written as [72] The expectation of the difference is used to extract the watermark which is expressed as follo765ws .

QUANTIZATION INDEX MODULATION The quantization index modulation (QIM) is a technique which uses quantization of samples to embed watermark. The basic principle of QIM is to find the maximum value of the samples and to divide the range 0 to the maximum value into intervals of step size Δ. The intervals are assigned a value of 0 or 1 depending on any pseudo random sequence. Each sample has quantized value, thus, a polarity is assigned based on the location of the interval. The watermark is embedded by changing the value of the median for created interval and by the similarity of the polarity and watermark bit. Fig Modification of samples using QIM

PHASE CODING [Watermarking the phase of the host signal] Algorithms that embed watermark into the phase of the host audio signal do not use masking properties of the HAS, but the fact that the HAS is insensitive to a constant relative phase shift in a stationary audio signal [71].

SPREAD-SPECTRUM WATERMARKING ALGORITHM Spread-spectrum watermarking scheme is an example of the correlation method which embeds pseudorandom sequence and detects watermark by calculating correlation between pseudo-random noise sequence and watermarked audio signal. BASIC IDEA The modulated signal is then added to the original audio to produce the watermarked audio x(n) such as x(n) = s(n) + αw(n) The detection scheme uses linear correlation. Because the pseudorandom sequence r(n) is known and can be regenerated generated by means of a secret key, watermarks are detected by using correlation between x(n) and r(n) such as

where N denotes the length of signal. Equation yields the correlation sum of two components as follows:

DOMAIN OF WATERMARKING The audio watermarking can be classified as 1.TIME DOMAIN WATERMARKING (Temporal watermarking). Temporal watermarking hides watermarks directly into digital audio signals in the time domain, time-domain audio watermarking is relatively easy to implement, and requires few computing resources, low cost, fast speed however, it is weak against signal processing attacks such as compression and filtering. 2.FREQUENCY DOMAIN WATERMARKING (spectral watermarking). whereas spectral watermarking methods hides watermarks in the transform domain. FFT, DCT, DWT,are commonly used transform.Frequency domain watermarking is very roubst again various signal processing attacks.

TIME DOMAIN AUDIO WATERMARKING In time domain watermarking techniques, watermark is directly embedded into audio signal. No domain transform is required in this process. Watermark signal is shaped before embedding operation to ensure its inaudibility .

FREQUENCY DOMAIN AUDIO WATERMARKING The input signal is first transformed to frequency domain where the watermark is embedded, the resulting signal then goes through inverse frequency transform to get the watermarked signal as output as shown in Figure . Watermark can be embedded into frequency


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