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FFT implementation on TMS320C5505

Lokesh Jadhav
Prodigy 20 points
Other Parts Discussed in Thread: TMS320C5505

Hello There,

I'm working on TMS320C5505 for FFT implementation.

Problem Statement:-

Need to detect the frequency of the input signal and then its magnitude by implementing FFT and also magnitude of its 1st Harmonics.

I'm new to dsp processor. So please help me to solve this problem. I've tried a code which I got inside the Application Note. But its not working and not easy to understand.

Please help me to solve this.! 

Thank You.!

 

 

  • 0
    TI__Genius 12805 points
    To understand better DSP theory get a good book

    Usually in order to find the basic frequency and the first harmonic one does FFT on periodic signal. The input signal may be real or complex, but the FFT is (almost) always complex. Each value correspondent to a frequency bin. The magnitude of the bin is the square of the real component plus the square of the imaginary component.

    Do FFT on the signal. Calculate the magnitude of each frequency bin. Find the frequency bin with the highest magnitude. The first harmonic is the double of the basic frequency.

    I hope it helps

    Ran
  • 0 in reply to ran35366
    TI__Genius 12805 points
    No response so I close the thread
  • 0 in reply to ran35366
    Prodigy 20 points

    Dear Ran Sir,

    Due to some urgent work, I was not able to be here.

    Thank You for your kind reply, but Sir as You said, I've already known the basics of the FFT and calculation.

    Actually I want you to tell me the implementation of FFT in the TMS320C5505.

    Recently I've referred the Application note and able to build a program, and getting the graphs of FFT

    but sir, I'm unable to trace the frequencies which the graph is showing and the values they are plotting, its a bit confusing. Can you please tell me how to interpret the graph and how to get the FFT values from the FFT magnitude graph

  • 0 in reply to Lokesh Jadhav
    TI__Genius 12805 points
    Here is my advice for you

    Based on the number of samples and the "sample rate" that you assign to the data, generate a pure sine wave with a known frequency and run it as input to the FFT function. Look at the output. (you may have to disregard the "negative" frequencies in the second half of the output).
    Then repeat the experiment with another frequency and see the location of the FFT results. Then you know how to translate results into frequencies.

    Now if you ask how to understand the frequency from the
    results, look at this URL (Do search for FFT frequency and sample rate)

    electronics.stackexchange.com/.../what-is-the-relation-between-fft-length-and-frequency-resolution

    Ran