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Output display of the FFT applet

A sample of the output produced by the FFT applet is shown in Figure 1 .

Figure 1. Transform of pulse with negative slope.
missing image

An examination of Figure 1 shows that the display produced by the applet contains two sections. One section is labeled f(x) and the other section islabeled F(k).

This is an interactive applet with the ability to transform the complex samples represented by f(x) into complex samples represented by F(k).Alternatively, the applet can be used to transform complex samples represented by F(k) into complex samples represented by f(x).

Real and imaginary sections

Each section contains two boxes, one labeled Real and the other labeled Imaginary. One box contains a visual representation of a set of real samplesand the other box contains a visual representation of a set of imaginary samples.

With one exception, each sample is represented by a black circle. In each box, one of the samples is represented by an empty circle. The empty circle represents an index value of zero. Samples to the right of the sample withthe empty circle are samples at positive indices, and samples to the left of the sample with the empty circle are samples at negative indices.

A complex sample

A pair of values, one taken from the Real box and one taken from the Imaginary box, represents a complex sample.

Any of the circles can be interactively moved up or down with the mouse. The value of each sample is represented by the distance of the correspondingcircle from the horizontal line.

When a change is made to the value of any sample belonging to either f(x) for F(k), the transformation is recomputed and the display of the otherfunction is modified accordingly. If you modify the value of a sample in f(x), the values in F(k) are automatically modified to show the Fouriertransform of f(x). If you modify the value of a sample in F(k), the values in f(x) are automatically modified to show the inverse Fourier transform ofF(k).

This is an extremely powerful interactive tool.

Powers of two

Many and perhaps most FFT algorithms require the input series to contain a number of complex samples that is a power of two such as 2, 4, 8, 16, 32,etc. Most FFT algorithms also produce the same number of complex samples in the output as are provided in the input. The FFT algorithm used in thisapplet is no exception to those rules.

A pull-down list at the bottom of the applet lets the user specify 16, 32, or 64 complex samples for both the input and the output. All of theexamples in this module use 16 complex samples for input and output.

Location of the origin

The applet also provides a check box that allows the user to cause the origin (the empty circle at index value zero) to either be centered or placed at the left end. The display in Figure 1 has the origin centered. Other displays that I will use later have the origin at the left end.

Other applet controls

The other pull-down list and the button at the bottom of the applet provide other control features that don't need to be discussed here. Istrongly urge you to download this applet and experiment with it. The results can be very enlightening.

Questions & Answers

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
Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
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?
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
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
I'm interested in nanotube
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
what is system testing
what is the application of nanotechnology?
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
I'm interested in Nanotube
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
can nanotechnology change the direction of the face of the world
Prasenjit 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, Digital signal processing - dsp. OpenStax CNX. Jan 06, 2016 Download for free at https://legacy.cnx.org/content/col11642/1.38
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