<< Chapter < Page
  Digital signal processing - dsp     Page 9 / 14
Chapter >> Page >

(The real and complex parts of the frequency spectrum were computed at 256 frequencies between zero and the sampling frequency.)

There were 256 values plotted horizontally in each separate plot. Once again, to make it easier to view the plots on the rightmost end, I plotted the valueson a grid that is 270 units wide. This leaves some blank space on the rightmost end to contain the numbers, thus preventing the numbers from being mixed in withthe plotted values. The last actual data value coincides with the rightmost tick mark on each plot.

Perform an inverse fourier transform

After modifying the complex spectrum as described above, the program performs an inverse Fourier transform on the modified complex spectrum to produce thefiltered impulse.

The filtered impulse

The filtered impulse is shown as the bottom plot in Figure 4 . As you can see, the pulse is smeared out in time relative to the input pulse in the top plot.This is the typical result of reducing the bandwidth of a pulse.

(This particular modification of the complex spectrum resulted in a filtered pulse that has the waveform of a SIN(X)/X function. A differentmodification of the complex spectrum would have resulted in a filtered pulse with a different waveform.

This example also illustrates one of the miracles of digital signal processing. Energy appears in the output before it occurs in the input.Obviously that is not possible in the real world of analog systems, but many things are possible in the digital world that are not possible in the realworld.)

Beginning of the class for Dsp037

Listing 8 shows the beginning of the class definition for the program named Dsp037.

Listing 8. Beginning of the class for Dsp037.
class Dsp037 implements GraphIntfc01{ final double pi = Math.PI;int len = 256; double[]timeDataIn = new double[len];double[] realSpect = new double[len]; double[]imagSpect = new double[len];double[] angle = new double[len];//unused double[]magnitude = new double[len];double[] timeOut = new double[len];

Listing 8 simply declares and initializes some variables that will be used later.

Beginning of the constructor

The constructor begins in Listing 9 .

Listing 9. Beginning of the constructor.
public Dsp037(){//constructor timeDataIn[32]= 90;

Listing 9 creates the raw pulse data shown in the topmost plot in Figure 4 .

When the array object referred to by timeDataIn is created, the values of all array elements are set to zero by default. Listing 9 modifies one of the elements to have a value of 90. This results in a single impulse atan index of 32.

Compute the Fourier transform

Continuing with the constructor, the code in Listing 10 uses an FFT algorithm in the method named transform (discussed earlier) to compute the Fourier transform of the impulse.

Listing 10. Compute the Fourier transform.
//Compute FFT of the time data and save it in // the output arrays.ForwardRealToComplexFFT01.transform( timeDataIn,realSpect, imagSpect,angle, magnitude);

Questions & Answers

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 ?
s.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
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.
Harper
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
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
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
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
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
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
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Good
Got questions? Join the online conversation and get instant answers!
QuizOver.com Reply

Get the best Algebra and trigonometry course in your pocket!





Source:  OpenStax, Digital signal processing - dsp. OpenStax CNX. Jan 06, 2016 Download for free at https://legacy.cnx.org/content/col11642/1.38
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Digital signal processing - dsp' conversation and receive update notifications?

Ask