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This module details the primary three algorithms explored for encoding digital data in audio as part of the fall 2008 ELEC 301 class project.


Our three encoding algorithms all begin the same way. First we take the user-defined constant for the number of segments and split the input signal in the time domain. Each segment represents a possible bit of hidden data. More segments mean more bits and a higher data rate, but it also means fewer samples from which to decode.

Whenever we wish to encode a one we alter the time chunk according to the algorithm. To encode a zero we leave the segment alone. After altering (or not altering) each segment, we take the Inverse Fourier Transform if needed and recombine them into our marked ŝ(t).

Frequency-masking algorithm (fma)

In this algorithm we take advantage of frequency masking. Since the human ear cannot hear quieter frequencies next to a louder frequency, we alter these values. To encode a one we find the Fourier Transform for each segment of time and find the max value of this transform. Then we scale the neighboring values on either side by some scalar α<1.

The case where the max value is close to the edge of our segment is slightly more complicated. We chose to alter the values on the non-edge side as normal and to alter as many samples on the edge side as existed.

We cannot encode a bit if the maximum value is zero or if the neighboring frequencies are too small (according to some predefined value).

Testing revealed that α = .5 was clearly audible for all of our test files, but α =.95 was not enough of a difference for the computer to reliably detect.

Diagram of frequency encoding algorithm

Diagram of Frequency Encoding Algorithm

Example of a change made by the fma

Example of a change made by the FMA to encode a 1

Phase-shifting algorithm (psa)

In this algorithm we take advantage of the fact that the human ear cannot hear slight variations in phase. To encode a one we find the Fourier Transform of each time segment and slightly alter the phase by a predefined value.

We cannot encode a bit if most of the values are zero.

Testing revealed that a phase shift of .25π is audible, while a phase shift of .001π became hard for the computer to detect.

Diagram of phase encoding algorithm

Diagram of Phase Encoding Algorithm

Example of a change made by the psa

Example of a change made by the PSA to encode a 1

Echo algorithm (ea)

Here we use the fact that our test suit is comprised of music and already have some amount of echo. Adding a slight amount more does not make an audible difference. To encode a one we shift the segment by some predefined value, de-amplify it by some scalar α<1, and add this echo back to the original segment.

We cannot encode a bit if most of the values are zero.

Testing revealed that an echo de-amplified to .2 was audible, while a de-amplification by .0001 was not reliably detected. Also a 30 sample delayed echo was inaudible to the human ear.

Diagram of echo encoding algorithm

Diagram of Echo Encoding Algorithm

Example of a change made by the ea

Example of a change made by the EA to encode a 1

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Elec 301 projects fall 2008. OpenStax CNX. Jan 22, 2009 Download for free at http://cnx.org/content/col10633/1.1
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