Forums Search for: FFT
FFT testing
inI'm in the process of testing a hardware floating point FFT. It is working well with the literally millions of vectors we have thrown at it,...
I'm in the process of testing a hardware floating point FFT. It is working well with the literally millions of vectors we have thrown at it, comparing well with a software FFT. The test vectors to date have mostly been example vectors taken from the application. Additionally, I tested it initially with the classic dual sines for a few selected cases while verifying the basic function,...
zero padding radix - 2 FFT
inFor starters, I'm still a newbie muddling my way through the various texts and fourier terminologies. I'm of the impression that given an FFT...
For starters, I'm still a newbie muddling my way through the various texts and fourier terminologies. I'm of the impression that given an FFT with an odd size. Zero padding the FFT to the next power of two amounts will do the trick. Barring efficiency reasons with regards to odd sizes, I'm only interested in how the padded and non padded version could be equivalent. Now utilizing matla...
Time varying FFT filtering
inHello folks, I know this topic has been discussed many times here, but I cannot seem to get a clear picture of what method should be used when...
Hello folks, I know this topic has been discussed many times here, but I cannot seem to get a clear picture of what method should be used when doing a time varying filter using an FFT. I have to use an FFT since I have to do signal analysis as well. Some discussions say that using the overlap-save method with a rectangular window is best, while others say that's the worst for a time vary...
Frequency band-shifting via an FFT.
inHello, What is the proper way, using an FFT, to shift a band of frequencies up or down? For example, supposed I have a voice signal...
Hello, What is the proper way, using an FFT, to shift a band of frequencies up or down? For example, supposed I have a voice signal between 300-3000Hz. I want to shift the 1000-2000 band into the 2000-3000 region (and vice versa). Is this doable with an FFT by any chance? Thanks, --Shafik
FFT of size 1536
inI just want to know how can we implement the FFT of size 1536. With reading the literature I came to know that we do it by splitting 1536 into...
I just want to know how can we implement the FFT of size 1536. With reading the literature I came to know that we do it by splitting 1536 into three block of 512 and then take their fft. In the end we combine all the ffts and multiply with the respective twiddle factors to and apply the radix 3 stage. Can anyone help me with the C coding regarding it. Suppose that I have done the coding for three ...
FFT By Decimation In Time paper or succinct explanitory resource
inHi All, I have recently completed my DSP course (subject) which is part of my engineering degree and I am very interested in DSP applications...
Hi All, I have recently completed my DSP course (subject) which is part of my engineering degree and I am very interested in DSP applications to Audio in particular. I have decided to undertake a project which involves FFT (probably I will use a Radix-2 to keep it simple for me) in hardware - I will be coding an FFT in VHDL. The main purpose of this project is to own the core functio...
Exocortex.DSP FFT implimentation? What should my result look like.
inHi There I'm fairly new to FFT and the like and I'm trying to implement the Exocortex.DSP for C# and I have it working but I'm not really sure...
Hi There I'm fairly new to FFT and the like and I'm trying to implement the Exocortex.DSP for C# and I have it working but I'm not really sure how to interpret to results? So I pass a 1024 sized array of floats (they are 16 bit audio samples, only the first 700 or 800 are actual values, I've zeroed the rest) to Fourier.FFT(myarray, 512, FourierDirection.Forward) So I'm wondering a f...
Daxon Scrambler Scam?
inHello DSP wizards, I am still not convinced of Daxon's "FFT Scrambler" shown here: http://www.daxon.ru/eng/daxon500.html They say that they...
Hello DSP wizards, I am still not convinced of Daxon's "FFT Scrambler" shown here: http://www.daxon.ru/eng/daxon500.html They say that they implement a band splitter scrambler using an FFT/inv FFT without any need of synchronization whatsoever. Is that really possible, even though they claim the audio quality is "excellent"? Im just wondering if theres something fishy about this. Than...
Something astray in my FFT understanding
inHi again all As you might know from my other thread Im implementing an FFT from scratch to get a better understanding of the whole...
Hi again all As you might know from my other thread Im implementing an FFT from scratch to get a better understanding of the whole time/frequency mapping. However Ive run into a bit of a roadblock. I have implemented small bit of code that takes N samples and performs a N point FFT. My code is running fine, it gives the same result as when I do it out by hand, so whats at fault is that my under...
FFT frequency shift
inDear all, The problem I am having deals with the FFT. We are acquiring signals from several measurements of electromagnetic fields in the...
Dear all, The problem I am having deals with the FFT. We are acquiring signals from several measurements of electromagnetic fields in the work-environment (for safety reasons) and we want to obtain the most exactly version of the signal in the frequency domain. Appart from the usual problems with FFT, leakage, Windows, resolution, etc. we have come the problem that the signals that we acquire (...
Phase scrambled FFT - Question from beginner
Hello, I am new to using FFT and I was wondering if anybody could point me in the direction of any scripts (C++ or Matlab) or any algorithm...
Hello, I am new to using FFT and I was wondering if anybody could point me in the direction of any scripts (C++ or Matlab) or any algorithm overviews to perform the following.... Computing the FFT of an image, setting the phase values to random values in the interval 0 - 2pie, while maintaining Hermitian symmetry, then backtransforming to produce a real image. Any help would be much ...
real input FFT for SDF architecture
inHi forum, I have a complex input FFT core implementation for FPGA. Now I want redesign the core to reduce the logic for real input...
Hi forum, I have a complex input FFT core implementation for FPGA. Now I want redesign the core to reduce the logic for real input sequences. I use SDF (single delay feedback) architecture. Output is 1 complex sample per clock. The standard 2N real FFT with N complex FFT doesn't work for me. The difference between 2N and N point FFTs is only one butterfly stage (one complex multiplication a...
proper terminology for one bin of an fft/dft?
inWhat is the proper or most common term for computing or describing only one bin of an fft or dft? I think this is the same thing as the...
What is the proper or most common term for computing or describing only one bin of an fft or dft? I think this is the same thing as the correlation against quadrature sinusoids of a frequency which happens to be an exact multiple of the reciprocal of the fft length. One bin can also be calculated by an implementation of the Goertzel algorithm, which I've seen described as a second order fi...
FFT result not symetrical?
inQuick question, I'm testing one of my own FFT routines with an input as a complex waveform, I'm not sure what kind of output i'm suppose to get,...
Quick question, I'm testing one of my own FFT routines with an input as a complex waveform, I'm not sure what kind of output i'm suppose to get, but one of the most obvious features is that the real part of the result is not symmetrical ... is it possible to get a FFT result with such a feature or is my routine incorrect? (This may seem like a really silly question!) If I input some samples ...
SNR calculation using FFT
inHi all, Currently, I use FFT to calculate the input single tone signal SNR and have a question about it posting below: SNR =...
Hi all, Currently, I use FFT to calculate the input single tone signal SNR and have a question about it posting below: SNR = 10*log10(|disired single bin magnitude|^2/sum(|all bins magnitude other than desired|^2)) 1. if I set N1 as the fft number at 1st time, so the number of elements in sum() @ denominator is N1; 2. if I set N2 as the fft number at 2nd time, and the number of elementsi...
Constant Q spectrogram Vs FFT Spectrogram?
inI am a newcomer to Spectrogram analysis. It is said, there are two kind of spectrogram, one is constant Q spectrogram(octave band...
I am a newcomer to Spectrogram analysis. It is said, there are two kind of spectrogram, one is constant Q spectrogram(octave band filter,logrithm of frequency ).The other is FFT spectrogram. I knew a little about FFT spectrogram.But I am not so sure what's the difference between them? advanced Thanks Simon
FFT for sequences of arbitrary lengths
inWhen I try to apply fft to sequence lengths which are not powers of 2 - I decided to extend the data with zeros to the next higher power of...
When I try to apply fft to sequence lengths which are not powers of 2 - I decided to extend the data with zeros to the next higher power of 2 and then apply fft. Problem is the transform has more coefficients than the input. We cannot just discard the excess clearly. (When i try to apply the inverse transform, I am too far away from the original signals) How do we deal with it in an Image ...
DFT point = decimated filter output?
inHi, I am struggling with some FFT interpretation. To me it looks that each sample of an FFT can be considered as the output of a process...
Hi, I am struggling with some FFT interpretation. To me it looks that each sample of an FFT can be considered as the output of a process consiting of downconversion, fitlering ,decimating. e.g .the DC bin output is calculated by: - downconverting the signal by 0 (hence doing nothing) - applying a very simple filter that has N taps equal to 1 (for an FFT of size N). - decimating the f...
SNR estimation using a windowed FFT
inHi, What is the best way to estimate the SNR of a sinusoidal signal in white noise using an FFT? For the best SNR estimate, is it better...
Hi, What is the best way to estimate the SNR of a sinusoidal signal in white noise using an FFT? For the best SNR estimate, is it better to do one long FFT or to break up into smaller FFTs to average the noise power? Also does windowing have an effect on the measured SNR? Thanks, Rizwan
question on taking FFT of a negative-time signal?
inHi all, I want to ask about taking FFT of a signal discrete-time whose indices are limited in [-6, +6] and with 13 data points. x[n]= 1,...
Hi all, I want to ask about taking FFT of a signal discrete-time whose indices are limited in [-6, +6] and with 13 data points. x[n]= 1, for n=-2 .. +2; 0, for other n in [-6, +6] However, in Matlab all indices start from 1, so I have to input this sequence as x=[0 0 0 0 1 1 1 1 1 0 0 0 0]; y=fftshift(fft(x)); since the indeces have been shifted, so the y has no zero imagin...