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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

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.
Damian
yes that's correct
Professor
I think
Professor
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
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What is meant by 'nano scale'?
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LITNING
scanning tunneling microscope
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how nano science is used for hydrophobicity
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Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
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
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if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
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
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Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
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Introduction about quantum dots in nanotechnology
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Loga
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
how did you get the value of 2000N.What calculations are needed to arrive at it
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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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