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When implementing your spectrogram algorithm, make the following assumptions:

  • use a Hamming window
  • the window length is N=256
  • zero-pad by a factor of 2
  • do not overlap

Here are some things to keep in mind:

  • do not vectorize your code or use MATLAB-specific helper functions that are not available on the tablet (such as zeros() or norm() ), as you want to make porting it to C as straightforward as possible.
  • Retain only half of the FFT output, as it is conjugate symmetric (make sure you know why!)
  • If X = Xr + jXi is a complex number, the magnitude squared operation computes Xr^2 + Xi^2.
  • Because power can vary by orders of magnitude, the Log computation is used to reduce the dynamic range of the spectrogram output; this is useful when visualizing the data.

If your input signal is 8192 samples long, then your spectrogram output can be thought of as a 256 x 32 real-valued matrix. Make sure to understand why. You can then use the image() or imagesc() functions in MATLAB to visualize the data.

Part 4: a c implementation of the spectrogram


Your task is to implement a C version of the spectrogram algorithm that you wrote in Part 3. Here are some guidelines for how to proceed:

  • Remember you are doing block-based processing. Every time process() is called, inBuf has N samples available to be processed.
  • Read Section 2.1 of the FFTW tutorial to understand the data structures and function calls of the FFTW library.
  • Remember that floating point is available on this processor.
  • Use the test vector to verify that intermediate operations are being computed correctly (e.g., multiplication, zero-padding, log function, etc.).
  • For extra credit , implement a scheme that allows for arbitrary overlapping. This may require modifying code in Lab4Activity.java

Scaling the output

The values of outBuf must be between 0.0 and 1.0. This is because the output values are directly mapped to RGB colors, with each color channel being 8 bits. As the spectrogram output is generally not in between 0.0 and 1.0, you will need to find an appropriate mapping.

One possible mapping is to linearly scale and saturate the spectrogram output; you must determine the scaling parameters experimentally by processing real audio data. Here is an outline of one way to do this:

  • Start up the GDB debugger and Resume with all breakpoints disabled.
  • While playing a loud tone (i.e., generate in MATLAB and play out through headphones), set a breakpoint right before your process() function returns.
  • Export the inBuf array to a file. Review Part 2: Exporting Variables to a File if you don't remember how.
  • Repeat this process for noise-only input.
  • Import the two files into MATLAB to determine a suitable dynamic range.
This method also enables you to verify the functional correctness of your C code by exporting the spectrogram output to a file.

Quiz information

Be able to describe the effects of windowing and zero-padding on FFT spectral analysis. Know basic properties of the Fourier transform, DTFT, and DFT. What are the trade-offs between block-based and sample-by-sample processing? Although we did not require you to implement it, understand the effects of overlapping when computing the STFT. Understand the basic Android project structure and the relationship between Java and C programming for Android.

Questions & Answers

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.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
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
characteristics of micro business
for teaching engĺish at school how nano technology help us
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
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
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.
what is the actual application of fullerenes nowadays?
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.
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?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
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
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Ece 420 fall 2013. OpenStax CNX. Sep 26, 2013 Download for free at http://cnx.org/content/col11560/1.3
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