Performing a 1024 point real input FFT using a 512 point complex FFT routine

Started by BobW in comp.dsp10 years ago 13 replies
FFT

I'm using a microcontroller (dsPIC30F3013) to do an FFT on some "real" data (from a microphone) and I don't have enough internal RAM to get...

I'm using a microcontroller (dsPIC30F3013) to do an FFT on some "real" data (from a microphone) and I don't have enough internal RAM to get the frequency resolution I need. I found a forum entry by Rick Lyons as follows: -quote- Does the dsPIC33 allow you to perform 512-point FFT on complex-valued input samples? If so, there's a way to perform a 1024-point *real-input* FFT using ...


Plotting of FFT graph in Excel

Started by sulphox in comp.dsp14 years ago 12 replies
FFT

Hi all, I wanna plot a FFT graph. Let's say i have variable, t y(t)=rect(t) Y(f)=FFT of rect(t) If i wanna plot the FFT graph. What should be...

Hi all, I wanna plot a FFT graph. Let's say i have variable, t y(t)=rect(t) Y(f)=FFT of rect(t) If i wanna plot the FFT graph. What should be the x and the y axis? is it 't' and 'absolute of Y(f)' respectively? Please correct me if i'm wrong. Thanks for any help in advance.


call FFT function from dsplib of vc5510

Started by swlow1016 in comp.dsp13 years ago
FFT

hi, i would like to ask is this the correct way to call FFT function from dsplib of vc5510 rfft(sinetable,256,SCALE); currently...

hi, i would like to ask is this the correct way to call FFT function from dsplib of vc5510 rfft(sinetable,256,SCALE); currently i am generating a 12 cycle sine waveform to test this FFT function. how should i configure so that i can get the FFT display under the single time display type.


Radix 4 FFT

Started by sudarshan_onkar in comp.dsp12 years ago 1 reply
FFT

HI, I am not bale to find some good stuff on radix 4 FFT which explains the algo. Only in P&M book it is explained to some extent but still not...

HI, I am not bale to find some good stuff on radix 4 FFT which explains the algo. Only in P&M book it is explained to some extent but still not as clear as radix 2. Please tell is there any material on radix 4 fft?


FFT Questions.....

Started by Todd in comp.dsp16 years ago 11 replies
FFT

I have had some experience with the DFT, and realize that the fft produces the same results, only faster. I understand the whole concept of...

I have had some experience with the DFT, and realize that the fft produces the same results, only faster. I understand the whole concept of resolution, that if 128 samples are taken at 10kHz, there are only 128 possible frequencies (all equally spaced from 0 to 10k) that can be absolutely determined. Is there an algorithm that performs a second fft of the same original signal, but over only ...


FFT in hw

Started by manishp in comp.dsp6 years ago
FFT

Sirs, Generally, when fft is imimplemented in hw, due to prohibitive silicon area, the intermediate stages are allowed only 2 bit (for eg)...

Sirs, Generally, when fft is imimplemented in hw, due to prohibitive silicon area, the intermediate stages are allowed only 2 bit (for eg) growth. If I simply see this from a mathematical perspective, we do lose a very significant amount of bits due to this. How come this is acceptable and widely used in many hw fft implementation s? Thanks, manish


FFT in hw

Started by manishp in comp.dsp6 years ago 1 reply
FFT

Sirs, Generally, when fft is imimplemented in hw, due to prohibitive silicon area, the intermediate stages are allowed only 2 bit (for eg)...

Sirs, Generally, when fft is imimplemented in hw, due to prohibitive silicon area, the intermediate stages are allowed only 2 bit (for eg) growth. If I simply see this from a mathematical perspective, we do lose a very significant amount of bits due to this. How come this is acceptable and widely used in many hw fft implementation s? Thanks, manish


FFT and IFFT problems on the Motorola 56F8323

Started by Shafik in comp.dsp15 years ago 11 replies

Hello all, I would REALLY appreciate if someone could help me figure out why my FFT and IFFT arent working on my Motorola chip. The chip...

Hello all, I would REALLY appreciate if someone could help me figure out why my FFT and IFFT arent working on my Motorola chip. The chip has the 56000e core. All Im doing is, taking an array of 16 Fractionals, that represents a sine wave. Im doing an in-place FFT then inverse FFT on it and the results are COMPLETELY off of what I would expect (Id expect the same sine wave back). I...


FFT TMS320F2812

Started by burnsheneger in comp.dsp13 years ago 1 reply
FFT

Hello, I need help with the following: I am using a TMS320F2812 DSP and I need to use a FFT with the size 64 samples. I want to know if...

Hello, I need help with the following: I am using a TMS320F2812 DSP and I need to use a FFT with the size 64 samples. I want to know if anyone have or know a FFT library working with a size like 64 or 128. Thanks a lot Bruno Coelho


What is the most effective way to do a zoom FFT

Started by Diego in comp.dsp14 years ago 1 reply
FFT

Hi. I'm working in a FFT project, and I need to do a zoom in a FFT. Do you know what is the most effective way to do a zoom FFT. Do you have...

Hi. I'm working in a FFT project, and I need to do a zoom in a FFT. Do you know what is the most effective way to do a zoom FFT. Do you have a code to do it? Thank you? Diego


Am I missing something obvious?

Started by Edison in comp.dsp12 years ago 7 replies

Hi I have recently started working with DSP systems. After a great deal of struggle with an EZ LITE KIT I have finally managed to get a...

Hi I have recently started working with DSP systems. After a great deal of struggle with an EZ LITE KIT I have finally managed to get a sensible result for an FFT, using an internally generated waveform for testing. Now for the problem: Now I have a reasonable looking FFT I thought I'd try and perform the FFT on two frequencies, the fundamental and its second harmonic. The strange thing i...


FFT algoritms

Started by Richard Owlett in comp.dsp12 years ago 37 replies
FFT

In "Chapter 12 - The Fast Fourier Transform / FFT Programs" of _The Scientist and Engineer's Guide to Digital Signal Processing_ Smith says...

In "Chapter 12 - The Fast Fourier Transform / FFT Programs" of _The Scientist and Engineer's Guide to Digital Signal Processing_ Smith says "There are also FFT routines that completely eliminate the bit reversal sorting." Could someone point me to a description of one, preferably with BASIC or FORTRAN sample code. TIA


Comparison between numerical precision in FFT and manual FT: both error plots show very different behavior

Started by alex singh in comp.dsp7 years ago 4 replies

Hi, I was hoping someone could help me understand the effects of the numerical precision in Matlab's FFT. I setup a very simple code that perform...

Hi, I was hoping someone could help me understand the effects of the numerical precision in Matlab's FFT. I setup a very simple code that perform the FFT and IFFT and compare my results to an FFT follwoed by a "manual" IFFT, I see a very strange increasing behavioir in the error and was wondering what this was due to. The fact that it increases with the sample number leads me to believe it's relat...


fft spectrum analyser using c6416 dsk

Started by nqobas in comp.dsp9 years ago 1 reply

hi everyone i have been allocated a project to design a fft spectrum analyser on the c6416 dsk board and also a power spectral density.the...

hi everyone i have been allocated a project to design a fft spectrum analyser on the c6416 dsk board and also a power spectral density.the problem i am not a strong c programmer. i know about fft algorithms but dont know how to omplement them on this board.can anyone tell me where to start and any fft algorithms that can be implemented on code composer studio.please help,confused student nqoba...


frequency analysis: number of fft coefficients effect the maximum value of the power spectrum?

Started by Michael in comp.dsp13 years ago

Hi! I wonder how to interpret the data after applying a Short Time FFT (fftw3 for real data) on audio samples (sinus tone 1400Hz). My goal...

Hi! I wonder how to interpret the data after applying a Short Time FFT (fftw3 for real data) on audio samples (sinus tone 1400Hz). My goal is to visualize the Energy in the frequency bands. First, I do a 512 point FFT on the whole audio file (frame shift without overlap) and the highest value after computing [1] re*re + imag * imag is about 9997 in a fft bin. Second, I do a 1...


testing FFTs

Started by Bob in comp.dsp16 years ago 13 replies
FFT

Hi Folks, A few weeks ago, I posted a query on FFT scaling. After your kind replys, I got it working. I was able to get the real only FFT...

Hi Folks, A few weeks ago, I posted a query on FFT scaling. After your kind replys, I got it working. I was able to get the real only FFT to work. By this I mean, there was no imaginary data input. However how does one test a complex FFT to make sure it is working? Is there a datafile that could be generated and what would the output result look like? Also...In what sort of appli...


Know Of Any Good FFT Implementation Resources?

Started by eric06 in comp.dsp13 years ago 1 reply
FFT

Hello, I am currently in the conceptual stages of implementing an FFT function in a relatively large FPGA (the thing has 6 multipliers that...

Hello, I am currently in the conceptual stages of implementing an FFT function in a relatively large FPGA (the thing has 6 multipliers that come for free, I need the device anyway to do other stuff). I've had cursory exposure to the FFT by reading Oppenheim/Schafer, but I'm looking for some material that will go deeper with the concepts and that will address practical implementation issues m...


Split complex vectors and AltiVec FFT's

Started by Eric Raas in comp.dsp16 years ago 4 replies

Hi - I am trying to use Apple's AltiVec FFT routine fft2d_zrip in a scheme for doing 2D sinc interpolation by zero-padding the 2D DFT of an...

Hi - I am trying to use Apple's AltiVec FFT routine fft2d_zrip in a scheme for doing 2D sinc interpolation by zero-padding the 2D DFT of an image. I am able to do forward and reverse 2D FFT's and recover the original image, but when I zero pad I get clearly wrong results. The FFT routine in question makes use of what Apple calls a "split complex vector" format, which is a reordering...


normalised cross correlation by FFT

Started by sangthong in comp.dsp11 years ago 2 replies

Hi, I have a problem of doing normalised cross correlation by FFT, which the result doesn't satisfy with the result from the one from time...

Hi, I have a problem of doing normalised cross correlation by FFT, which the result doesn't satisfy with the result from the one from time domain method and I don't know where it goes wrong. From my understanding, this is the cross covariance in frequency domain, which gives me the correct result. (If there are signals x and y) 1) Do FFT of x 2) Do FFT of y 3) Conjugates 1) or 2) 4) M...


2D FFTW Inverse FFT does not give original image when /n

Started by adam3914 in comp.dsp11 years ago 4 replies

I have what I have to assume is a stupid mistake on my part. I am able to take the fft of an image and get back the half of the transformed image...

I have what I have to assume is a stupid mistake on my part. I am able to take the fft of an image and get back the half of the transformed image as I should. When I try to do a inverse fft on the data from the fft I get really big numbers like 10^71 size numbers. When I would expect to get my original image times 640*480, the size of my image. My first question is do I have to create the othe...