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Altera_Forum's avatar
Altera_Forum
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16 years ago

FFT IFFT Unity gain output

Hello,

I am using the DE2 board (cyclone II fpga) for my project.

I took sound input using the internal audio codec (in 16 bit mode) then I pass it through FFT and then IFFT block. Finally i use the audio codec again to output the sound and hear it in the speaker.

My problem is that, when i make the FFT IFFT pair unity gain, using a scalar block, always there is a audiable noise in the output. The fft window size i have used is 128.

for scaling I followed the fft manual's procedure. I scale the output with the factor,

exp_out = exp_fft + exp_ifft + 7; // 7 is for the window size.

Should there always be a noise, when i scale? How to minimize it?

Please help...

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    16 years ago

    my project is took sound to FFT but i dont give output to speaker.Ijust display it to VGA.can u give me your code so we can repair it?

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    15 years ago

    I am having trouble dealing with the scaler.v file to create my own scaler and implement it on FFT - IFFT block. I'm using DE2 board as well. Setting a 128 points and 16 bits. I am thinking that with the fft of 128 points and ifft of 128 points, we would get 256 points of the entire block. That makes the FFT engine to have a max of -11 to min of -3 by referring to Table A-1 on the FFT Megacore Function User Guide. However, I am still having hard time dealing with the scaling codes. Can anyone please help me out here?