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We will now look at aliasing and its effect on the sampled signal. As you know, aliasing exists whenever signal frequencies greater than Fs/2 are sampled using a sampling frequency of Fs. To eliminate aliasing, most sound cards and DSP boards have some sort of built-in analog anti-aliasing filter that removes all input signals greater than a certain frequency prior to sampling. It is important to remember that anti-aliasing filters must do the filtering prior to sampling – otherwise, the high-frequency signals would have already aliased to lower frequencies by the sampling process.

Aliasing

This section has different instructions for the Speedy 33 and the 6711. Please select the section of the SPEEDY-33 or the 6711 based on the hardware setup on your station.

Speedy-33 instructions:

We will now look at aliasing and its effect on the sampled signal. As you know, aliasing exists whenever signalfrequencies greater than Fs/2 are sampled using a sampling frequency of Fs. To eliminate aliasing, most sound cards and DSPboards have some sort of built-in analog anti-aliasing filter that removes all input signals greater than a certain frequency prior tosampling. It is important to remember that anti-aliasing filters must do the filtering prior to sampling–otherwise, the high-frequency signals would have already aliased to lowerfrequencies by the sampling process.

Some boards (and most Soundcards) have anti-aliasing filters with variable cutoff frequencies that removeall frequencies>Fs/2. As Fs changes, the cutoff frequency of the anti-aliasing filter changes as well. If a boardhas a variable frequency anti-aliasing filter that is always set to Fs/2, there will never be aliasing (at least in theory). Althoughthis type of operation is ideal from a performance point of view, it doesn’t allow the user to examine the effect of aliasing. The SPEEDY-33 does not have an anti-aliasing filter. Any frequencygreater than 24kHz can cause aliasing if the sampling frequency is set to 48kHz.

  • Set the sampling frequency to 48000 Hz (in both the Analog Input and Analog Output nodes).
  • Set the function generator to a 0.2 V, 100 Hz, sinusoid.
  • Move thearrows on the function generator so that the hundreds-digit on the frequency display is flashing.
  • You can now easily increase the frequency in steps of 100 Hz. by pressing thebuttons.
  • Run the program and observe the frequency display, time display, and sound as you sweep the signal frequencyfrom 100 Hz. to 50 kHz.
  • Pay particular attention to the amplitude and sound of the reconstructed signal for input frequencies>24 kHz.

Answer these questions

Describe what you hear and see (especially the frequency spectrum) when you sweep the sinusoid frequency from 100 Hz. to 50 kHz. Take special note of what happens to both the amplitude and frequency of the reconstructed sinusoid once you get past 24 kHz.

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  • Repeat the experiment above, but set the sampling frequency to Fs = 8000 Hz. Here, pay special attention to what happens onceyou get above 4 kHz.

Answer these questions

What happens to the amplitude of the reconstructed signal once the input signal frequency hits 24 kHz? Explain.

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Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
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
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
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biomolecules are e building blocks of every organics and inorganic materials.
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research.net
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sciencedirect big data base
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Introduction about quantum dots in nanotechnology
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nano basically means 10^(-9). nanometer is a unit to measure length.
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characteristics of micro business
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Anassong
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
NANO
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
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.
Tarell
what is the actual application of fullerenes nowadays?
Damian
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.
Tarell
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.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
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
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
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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
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what is biological synthesis of nanoparticles
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Source:  OpenStax, Fundamentals of digital signal processing lab. OpenStax CNX. Jan 03, 2006 Download for free at http://cnx.org/content/col10303/1.5
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