Questions tagged [window-functions]

In signal processing, a window function is a mathematical function that is zero-valued outside of some chosen interval.

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27
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3answers
14k views

What should be considered when selecting a windowing function when smoothing a time series?

If one wants to smooth a time series using a window function such as Hanning, Hamming, Blackman etc., what are the considerations for favouring any one window over another?
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3answers
5k views

FFT with asymmetric windowing?

Common non-rectangular window functions all seem to be symmetric. Is there ever a case when one would want to use a non-symmetric window function before an FFT? (Say if the data on one side of the ...
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9answers
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Why do we use window in time domain rather than do FFT modify the spectrum and than inverse FFT

I thought that DSP would be done by using FFT of portions of a signal, modify the samples that result from FFT (since they represent the spectrum of our signal + noise) and remove any unwanted signals ...
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3answers
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A few questions about Slepian and generalized gaussian windows

I'm trying to add documentation for all the window functions in scipy.signal, and I'm stuck on the Slepian (same as DPSS?) and Generalized Gaussian windows, which I'd never heard of before. There are ...
9
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2answers
22k views

How do I apply a function window to a signal?

How can I apply a window function like Hamming or Lanczos to a signal, using its coefficients? I mean, which method can I use to do this? FFT? Convolution? Which method has the better performance?
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2answers
4k views

Why would one use a Hann or Bartlett window?

Suppose we're designing a low-pass FIR filter, and I want to use one of these three windows: Bartlett, Hann or Hamming. From Oppenheim & Schafer's Discrete-Time Signal Processing, 2nd Ed, p. 471:} ...
9
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3answers
5k views

What is a good FFT window function to reject DC?

I'm using an FFT to analyze what is essentially the power envelope of a signal (see here for info on the containing project), and, since power numbers are always positive, to eliminate the DC ...
9
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3answers
11k views

Is it customary to correct for the gain of a window?

Consider how the Hanning window is defined: 0.5 - 0.5 * cos(n*2*Pi/(N-1)) By this definition, it has a gain of 0.5, which is simply the average value of the ...
8
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2answers
3k views

Effect of windowing on noise

I understand that truncating a signal in time 'smears' the frequency response depending on the window chosen. In general, the shorter the signal duration, the more 'flattened' the frequency response, ...
8
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2answers
1k views

Why are there so many windowing functions?

Many windowing functions are listed here in the Mathematica documentation. I tried using a few to reduce leakage when computing a Discrete Fourier Transform. From what I could tell it made little ...
8
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2answers
2k views

Fourier transform artifacts

My starting point in what follows is a radially symmetric random field. Taking the Fourier transform of this (and plotting it in logarithm to highlight the patterns), I obtain the following image in ...
8
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1answer
1k views

Is the discrete Gaussian kernel an eigenfunction of the DFT?

So the Gaussian function is an eigenfunction of the Fourier transform because it transforms into itself, right? But this isn't true for the sampled Gaussian in the DFT because the tails of the ...
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5answers
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Does windowing affect Parseval's theorem?

I have computed Fourier transform from ecg data.It does obey Parseval's theorem, relation $$\sum_{n=0}^{N-1} \Big| x[n] \Big|^2 = \frac{1}{N} \sum_{k=0}^{N-1} \Big| X[k] \Big|^2$$ is fulfiled. ...
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2answers
1k views

Is spectral leakage due to windowing 'different' for the DTFT and DFT?

I'm currently trying to improve my foundational understanding of spectral leakage due to windowing. The more I have been reading about it, the more I'm starting to think that 'windowing spectral ...
6
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1answer
10k views

STFT: why overlapping the window?

For STFT, we impose window of certain size onto the original signal, then we perform fft on each window. The uncertanty about frequency and time is determined by the width of the window, however, I ...
6
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3answers
8k views

RMS calculation in frequency domain after windowing

I can calculate RMS in frequency domain as derived from Parseval's Theorem. But what if I have applied a windowing function before doing the FFT (in my case a Hann window)?. Now the RMS values are ...
6
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1answer
5k views

How to compute the main lobe width of generalized Hamming windows (i.e. Hann, Hamming, etc.)?

Is there a way to compute the main lobe width of windows of the generalized Hamming window family (i.e. Hann, Hamming, etc.)? By main lobe I mean the first zeros left and right of the center of the ...
5
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3answers
7k views

Effect of windowing on FFT magnitude

I have 2 sin waves: Fs = 1500; N = 100; t = (0:N-1)'/Fs; sinwave = sin(2*pi*15*t); sinwaveshifted = sin(2*pi*15*t + 1.3); If I get the magnitude at 15Hz using ...
5
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3answers
4k views

I need advice about how to make an audio frequency analyzer

I just need some clarification of some very basic aspects of creating a frequency analyzer. I am writing a c++ program, so far it is just a media player, with a custom explorer. You can make ...
5
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1answer
22k views

Why should one use windowing functions for FFT?

So I just revised my pitch calculation algorithm using a harmonic product spectrum algorithm. I was just curious about why this explanation of Harmonic Product Spectrum states that you need to ...
5
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2answers
10k views

python scipy fft on numpy hanning window smears peaks

I have a signal that I have acquired from an experimental instrument, that I wish to examine in the frequency domain. I don't care about phase for this exercise, I only care about magnitude. I ...
5
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2answers
6k views

Extracting accurate phase and amplitude information from FFT with an arbitrary number of samples

This is a followup question to one I asked earlier based on the chat after the answer given by @hotpaw2, and cross-posted from stackoverflow since it was suggested it is more relevant to DSP. I have a ...
5
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1answer
590 views

Spectrum Analysis using Windowed FFTs

I have a couple of questions regarding windowed FFTs: Why is the noise floor higher with windowed FFTs (according to Wikipedia's spectral leakage page, anyway), when the whole point of windowing is ...
5
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3answers
163 views

Window functions with rippleless spectra

On Wikipedia I found the Hann-Poisson window, and the article claims the spectrum is smooth, but it isn't theoretically smooth, as it turns out. In practice you achieve partial smoothness by jacking ...
4
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1answer
16k views

How should I select window size and overlap?

I'm new to DSP and I have a wav file with a number of different frequencies playing at different volumes. I'd like to plot the power of the 350Hz frequency signal at each point in time. The source is ...
4
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4answers
12k views

Choosing the right overlap for a window function

On Wikipedia there is quite a list of window functions. However, when you are doing a lot of STFTs, you often have to have some overlap to get better results. Generally an overlap factor of 2 (i.e., ...
4
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2answers
2k views

Whats the optimal window function to use for analyzing real-time data samples?

Say you wanted to run a X point FFT on the last X audio samples that were played. The problem being, using a normal hann window function would place emphasis on the "middle" of the audio sample. ...
4
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1answer
784 views

Optimal window function for amplitude estimation?

Assume you want to estimate the amplitude of a known frequency sinusoid in additive Gaussian (white or pink) noise. Also assume mainlobe width/sidelobe decay doesn't matter. Windows should be ...
4
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1answer
2k views

What is the relation of the transition band's width and the filter order for the FIR windowing method

When designing an FIR filter using the windowing method, how can one estimate the filter order ? It's obvious that the type of window and the transitions band's width has some effect on the order.
4
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1answer
69 views

Amplitude Estimating Using a Windowed DFT

Let's say we want to estimate the amplitude A of a mono-frequent signal using a windowed DFT. The frequency of the signal is unknown, and the frequency resolution of the DFT is limited, thus it cannot ...
4
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1answer
2k views

Matching masked images

Let's say I have two images that are parts of the same bigger image, cut using two masks (for simplicity, let's assume that the masks are just rectangles of the same size). The images are presumed to ...
4
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1answer
1k views

FFT averaging with different block sizes - how to scale the amplitudes

I need to analyze a real-valued time signal with a length of 300000 in the frequency domain. The sampling frequency is 100000Hz. In order to increase the signal-to-noise ratio reduce the "fine-grain" ...
4
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2answers
4k views

Effect of Hanning Window on phase of FFT

I'm calculating the beat of song through the frequency domain. I have 60 seconds of audio sampled at 48000Hz, multiplied by a Hanning window in the time domain. This gives me a resolution in the ...
3
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2answers
7k views

Why is each window/frame overlapping?

I am currently reading up on some speech recognition theory. As it speech signals usually are non stationary, but if a speech is seen in a very small time frame can it be deemed stationary, as would ...
3
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3answers
5k views

Zero-pad before or after windowing for FFT

What's the correct way. Should I zero-pad a signal before or after applying a windowing function?
3
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1answer
90 views

How to do continuous signal processing (i.e without windowing)?

I'm working in speech recognition research, and I wonder if there is a way to analyse sound just like how ears do (i.e. without windowing), so for example to take some feature continuously with an ...
3
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2answers
181 views

Zero padding - High amplitude

I have a set of 512 samples that I have collected with a sensor. I'd like to apply zero padding to it, for better frequency bin resolution. However, all the tutorials I see to make this occur center ...
3
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1answer
175 views

The higher the sidelobes of a signal frequency spectrum, the greater the “cross-talk” between transmission channels

Why is that 'The higher the sidelobes, the greater the "cross-talk" between channels' when transmitting signals via hardware electronics? where, Cross-talk: a signal transmitted on one circuit or ...
3
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1answer
5k views

What is the difference between Filters and Windowing?

I'm finding some difficulties to understand the difference between Filters, and Windowing. accoriding to my understanding both filters and window functions will make changes to the input signal ...
3
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2answers
1k views

At which point in the signal processing chain to use Hann Window?

I have a question about signal processing. Experienced with embedded design and code, but DSP is in new territory. Thus far I am using the CMSIS DSP library functions, which are working well. I am ...
3
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2answers
1k views

Working around FFT windowing?

I have the following problem, that I ran into recently, when calculating the spectra of data that I obtain from a measurement technique, we are using in our group. In short what we do in the ...
3
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1answer
307 views

What windowed Sinc might be closest to a Parks–McClellan low-pass filter?

In another question on dsp.stackexchange, a statement was made that the output of MATLAB firpm() or firls() for an anti-alias low-pass filter was "close" to the coefficients of a windowed-Sinc low-...
3
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1answer
925 views

What is the physics behind the width of a main lobe?

We know that the square window gives the lowest main lobe width possible, and that other windows after that trade main lobe width for side lobe height. I also understand that the main lobe width is ...
3
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1answer
308 views

Channel Vocoder producing output with “click” sounds

I'm trying to make a channel vocoder that takes two inputs, one a frequency rich carrier (a musical sound) and the other a modulator (vocals). Applying operations involved in the channel vocoder ...
3
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1answer
129 views

FFT strong signal in middle frequency bin

I've developed a radar that I'm using to determine the distance to remote objects. It uses a custom PCB with an onboard FPGA that performs the DSP algorithms. The data from it is then plotted on a ...
3
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1answer
173 views

Overlapping power-of-cosine windows with constant weight

I would like to refer you to a relevant question I posed on the Math StackExchange: A generalisation of the Pythagorean trigonometric identity. As can be seen from the question and the answer, what ...
3
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3answers
1k views

A question about spectral leakage

I have read about spectral leakages in other posts here. From what i understand, it occurs because you dont have an integer number of time periods in your sampled data. By default a rectangular window ...
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5answers
730 views

To what extent can we see signals that fall between frequency bins?

I have a simple problem I would like to figure out for fourier analysis of seismic data. Let us say that we have a signal $z[n]$, of length $N$. If I take its (same size) FFT, I will get $Z[k]$, ...
2
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4answers
798 views

Windowing function squared?

Reading this paper about WSOLA (Verhelst, Roelands) (PDF) At page 2 there's a "time-warped STFT's synthesis function" involving $v(n)=w^2(n)$ which is a windowing function. A windowing function ...
2
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4answers
2k views

Intuitively, why is windowing function a low-pass filter?

I'm trying to intuitively understand why a windowing function of a signal is a low-pass filter. I know its DTFT is a sinc function, making it mathematically a low-pass filter, but my logic says ...

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