Digital watermark

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					                    Audio Watermark
                             Jiamian Yang

Abstract
The recording industry is losing money. Piration should be blamed. But

are there any way to prevent the trend? Yes, the answer lies in the

watermark technology. In my paper, first I will talk about the original and

definition of audio watermark. Then the main idea, that is to say, the

mechanism behind watermark will be discussed. Thirdly, properties

would be elaborated. Then different applications are discussed. The last

but not least, a vivid case in real life is presented.



Introduction
According to figures published by the IFPI, the recording industry lost

4.2 billion dollars almost every year. The illegal manufacturer burn CDs

and sell them to the customer, who can buy the same CD the tenth price

as in some music store. What is more, some website provide download or

online listening service to music fans. However, an audio watermark

breakthrough the recording industry needs. Actually the audio watermark

is like a signature, different to every copy and piece of music. It could be

used to track the owner of illegal distribution and could be also used as a

copyright for the owner. Naturely, it has to make sure that it could not be
heard and interfere with the original sound quality and it could survive

the audio signal distortion. In my paper, first I give the origin and

definition to audio watermark, so to say, what is watermark, audio

watermark, where does it come from. Secondly I will discuss the main

idea behind the technology and then one of them-bitstream watermark.

Third, properties of audio watermark would be elaborated. That is what

requirement of an audio watermark should be met. The forth, I will talk

about the applications of audio water, how it could be used? The last but

not least, a special case of music trace company is presented. I will

concentrate on several business module based on the audio watermark

technology.



Audio watermark-Origin and definition
Actually, the word watermark comes from paper industry first. A

watermark is a design embossed into a piece of paper during its

production and used for identification of the paper and papermaker. The

watermark can be seen when the paper is held up to light. The design

could be some pattern or images which indicate quality of trademark of

the paper. Then the word watermark in introduced to digital field. It is an

identification code carrying information about the copyright owner, the

creator of the work, authorized consumers and so on(1). The watermark is

invisible and permanently embedded into digital data for copyright
protection and for checking if the data has been corrupted. The electronic

documents which is watermarked can be digital image, audio or even

video. But I will only concentrate on the audio watermark, which means a

watermark embedded in an audio stream to identify its origin.



The main idea


All watermarking system consist of two blocks-watermark embedding

system and a watermark detector system as we can see in picture one

Picture one:
In the watermark embedding block, a copyright owner uses a private key

to create an inaudible watermark on the audio file. So the private key is

used to encode the digital watermark into the music. Later on, the owner

can examine whether a given audio file, which us suspected for being

illegally copied, contains his or her own watermark and use it as legal

prove. In the watermark detector block,   a public key is used   to decode

the watermark from the music. The basic scheme contains a lot of

possibilities both for compressed file and for uncompressed files. Below

is how the audio watermark is embedded into the compressed files such

as MP3.

Picture 2




The mechanism is called bitstream watermarking.
Properties of audio watermark


Some basic requirements should be met by an audio watermark. These

are low computational cost, no distortion of original signal and change of

format, robustness and imperceptibility.

Low computational cost means it should not take long for a watermark to

be embedded and detected. It is a crucial factor in the watermark system.

The watermark imbedded in the audio file should in no way reduce the

quality of the audio file and change the format. If a watermark is

embedded in an MP3 file, the customer can also play it on some MP3

supported player, they do not need to buy a new player again. Robustness

refer to the ability to detect the watermark after common signal

processing operations and hostile attacks. Example of common operations

performed on audio files include noise, reduction, volume adjustment or

normalization, digital to analog conversion and so forth. As far as attacks

concerned, there is different kinds of attack on the audio watermark. They

are collusion attack, signal diminishment attacks and inversibility attacks.

A collusion attack is having copies of audio files with the same

watermark, the attacker estimate the value of watermark by averaging the

value of the audio signal. Only about 10 samples are enough for such

estimation. As a coutermeasurement to this kind of attack, it is better to

embed more than one watermark in an audio file or embed different
watermark for different files. The signal deminishment attack refer to

different signal operation such as lossy compression, modulation,

conversion, etc. Now it is possible to embed more than one watermark in

a audio file. If Bob steals the watermarked one from Alice and watermark

it with his private key. It is sure to find Alice’s watermark in Bob’s file,

but vice versa not possible. However, an attack to this procedure is

created. So it is hard to decide who is the real owner of the audio file(2).

The other property of audio watermark is imperceptibility.     There should

be almost no difference between the watermarked one and the

unwatermarked one. Here is a sound wave graph of the same music with

and without watermark. As we can see, there is only small changes which

could not be noticed at the first sight and could also be ignored.

Picture 3
Applications

The audio watermark is used in many ways. First, it is used in proof of

ownership. Information during production, copyright information in the

form of a watermark can be anchored directly in the recording. Specific

ownership has different information imbedded. It could also used for

access control, the watermark becomes a trigger to give allowance for

playing the music. Tracing illegal copies is also an very important

application. Personalized information is embedded in the music. The

personalized information could be the customer number which moniter

the trace of the music. If such music is found in internet, the watermark

will be distracted and the customer number could be known for later law

actions.
Case study


Watermark is used in real life business. The fraunhofer institution in

Germany invented the watermark embedding technology and sold it to

the company music trace. Company music trace unfold two main

business module based on the technology. They are watermark

embedding for audio signals and internet search for illegal use. The

company use specific software to listen on the internet all day and night

and search the matched music. Of course, the customer should provide

several criteria for selecting the music first. For example, the music with

specific title should be caught. Then the watermarks would be distracted

as evidence. But only transaction numbers or customer numbers could be

extracted. The identity of original purchasers can only be determined by

the customers self.

Another business module is watermark embedding for audio signals.

Copy right information, recipient information and title information could

be imbedded. The imbedded content is different. The Product family

contentmark permits embedding a digital watermark in audio signals.

Depending on the product, this can involve either uncompressed or

compressed audio signal(3). ContentmarkPCm is a technology to embed

watermark in uncompressed files and the watermarked files are still

uncompressed files. The result is unchanged. The file could be PCM files
or Wave files. The contentmarkCD technology make it possible to create

different watermarks on the same copy files. ContentmarkMP3 is used in

compressed files.



Conclusion
As the conception watermark goes into digital area, recording industry

has some hope not to lose money. But it needs time. The watermark is

used as a special identification for every audio file. Different watermark

algorithm and scheme have been developed. Nevertheless, it should be

expanded and amended to cope with malicious attacks.



Reference

1. www.wikepedia.org

2. page 75, multimedia security, steganograghy and digital watermarking

   technique for protection of intellectual property, Chun-Shien Lu

3. www.musictrace.de/products/contentmark.en.htm