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This module details the testing methods used to compare the three methods of encryption (frequency, phase, and echo) studied as part of the fall 2008 ELEC 301 class project.


Aural tests

As our primary objective was to make the changes inaudible, we tested all of our algorithms aurally.

We initially tested the algorithms on a 440 Hz tone to ensure that the algorithms were working as expected. (We did not test the FMAon the tone as doing so would have been silly because the tone only has a single frequency with no other frequencies to modify.)

We continued our aural testing with a suite of six songs from different genres: classical, hip-hop, oldies, pop, rock, and techno.We adjusted any thresholds and predefined constants to the point of aural imperceptibility. Working within these limits we were then able to modify theseconstants to maximize bitrate, accuracy, and noise resilience.

The following figure details the particular songs chosen and their overall frequency spectrums.

Frequency spectrums of test suite songs


Our test suite had a CD quality sampling frequency: 44100Hz, which amounts to 220500 samples for a 5 second long clip.Ideally with no noise it would be possible to use a segment length of 2 samples. This setup translates to 220500/2 = 110250 segments in 5 seconds and 110250/5 =22050bits/sec. I.e. at CD quality, we cannot get more than a 22Kbits/sec data rate.

In practice we found that Mat lab was unable to handle this amount of data. We were, however, able to successfully reach 4800segments, or 46 samples per segment. These values translate to 220500/46 = 4793 segments in 5 seconds and 958bits/sec. I.e. we reliably demonstrated a 1Kbit/secdata rate.

Power ratios

To measure how much we had changed each of the signals by encoding bits, we took a power ratio of the original signal to theoutput signal.

Formula for power ratio

Formula for Power Ratio

We found these ratios for two different input characters: ‘@’ and ‘w’. Because ‘@’ is encoded by 100 0000 in ASCII, thesepower ratios measure the minimum amount of change we make to our signals. Because ‘w’ is encoded by 111 0111 in ASCII, these power ratios measure themaximum amount of change we make to our signals.

Power Ratios
@ w @ w @ w
classical 1.0052 1.0362 1.0056 1.0352 0.9992 0.9955
hip/hop 1.0079 1.0507 1.0068 1.0413 0.997 0.9818
oldies 1.0133 1.0747 1.0069 1.0425 0.9986 0.9897
pop 1.0115 1.0776 1.0063 1.0388 0.9975 0.9842
rock 1.0131 1.0628 1.0072 1.0419 0.9975 0.9888
techno 1.0155 1.0897 1.0077 1.0463 0.9951 0.9723

Table 1. Power Ratios for each algorithm encoding one 1 per seven bits (“@”) and one 0 per seven bits (“w”)

Chart of Power Ratios

The most important feature of these results is that all of our power ratios are very close to one, indicating that we have notchanged the signal very much.

We also see some variation across the different songs because which values are changed and by how much depends on the song; forexample, with the PSA, the delay causes us to drop samples at the end of the segment, and the power in the dropped samples depends on the song.

As expected, for ‘w’, the power ratio is further from one as more one-bits are encoded. Because adding an echo can be variouslyconstructive or deconstructive, the power ratio does not reflect the number of one-bits as much as FMA and PSA. This fact also explains why the power ratiosfor the EA are generally lower than those for the FMA and PSA.

Finally for FMA and PSA the power of the marked signal was lower than the power of the original signal. For the FMA, thisdecline in power was expected because we scaled frequencies down, thus, deceasing the power in the frequency spectrum, which, as Parseval’s Theoremtells us, corresponds to decreasing the power of the signal. For the PSA, this decline in power was also expected because the PSA delays the signal in varioussegments, dropping samples in the marked signal. The EA was the only case in which the marked signal had greater power than the original signal because theechoes in this case were more constructive than destructive.

Questions & Answers

Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
analytical skills graphene is prepared to kill any type viruses .
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
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.
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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