Questions tagged [window]

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6
votes
3answers
15k views

Moving average vs. Moving median

I have read in many places that Moving median is a bit better than Moving average for some applications, because it is less sensitive to outliers. I wanted to test this assertion on real data, but I ...
4
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3answers
2k views

Correct method for processing FFT in realtime

I am attempting to build a 'live' FFT for continuous analysis of an audio signal. I am relatively new to this, but have attempted the full thing, and then updating the graph at 20Hz refresh rate. My ...
4
votes
1answer
198 views

What is the LOW frequency resolution rule analogous to Nyquist?

If I'm analyzing a signal in the frequency domain, I know about the well known Nyquist criteria that the sample frequency must be > 2x of the highest component present in the signal. However, there ...
3
votes
2answers
6k 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
votes
2answers
161 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 ...
2
votes
1answer
59 views

What is the proper way to filter out unwanted noise from accelerometers?

I'm a beginner in signal processing and have a hard time to filter out environmental noise from the floor vibration data collected using accelerometers. I have tried using butterworth filter (IIR) ...
2
votes
1answer
251 views

Hanning and Hamming Window

I am new in the field of signal processing. What's the different between Hamming and Hanning window? When we use the former and latter?
2
votes
2answers
102 views

Fundamental misunderstanding of windowing

I believe I have a fundamental misunderstanding of windowing. I thought that windowing is applied to a signal with pointwise multiplication, then some sort of filtering is then done to it (say using ...
2
votes
2answers
3k views

Understanding overlapping in STFT

I understand the concept of the STFT. In order to avoid spectral leakage, you use a Hann window that overlaps by 50%. However, the problem that I have, is that the example code online does not account ...
2
votes
1answer
1k views

How is a signal multiplied with the window functions?

How the input signal get multiplied with the window functions like Hamming, Hanning, Blackman, etc? I have tried to multiply the input signal of $10\textrm{ MHz}$ sampled at $100\textrm{ MHz}$ using ...
2
votes
0answers
45 views

Separating out a sequence of DFTs with overlapping windows

Suppose I have a time series partitioned into $N$ equally-sized sections. Choosing some $k<N$, for each of the sections $i \in[0, N-k]$, I concatenate that section with the $k-1$ sections to the ...
2
votes
1answer
147 views

How to Calculate the Hann Low Pass Filter / Kernel for Image Processing

I'm currently studying for an exam in image processing and stumbled upon a exercise which i could not answer and my professor will not be available before the exam anymore. The exercise goes as ...
1
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4answers
307 views

What do I lose when I set overlap rate to a really high value in STFT

If I don't care about computational cost, is there any cons when I put overlap rate really high in STFT?
1
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3answers
3k views

Window period(overlap) and FFT

How does changing the window period (i.e the number of points overlap between two frames) affect the FFT results ? Suppose that a time series signal was converted to frequency domain by FFT with ...
1
vote
2answers
196 views

Non-symmetrical DFT of real valued signal

I have a homework assignment to take the $64$ DFT of $\cos((5\pi/32)n)$ and $\cos((5\pi/64)n)$. However, for the second case I obtained DFT spectrum such that I have that famous symmetry in real part ...
1
vote
1answer
529 views

Gaussian window and standard deviation

I am trying to figure out how to use the matlab gausswin function which constructs a Gaussian window for $N$ samples with a given standard deviation $\sigma$. The function is defined by ...
1
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1answer
449 views

Is an FIR filters 'transition width' frequency dependent?

I was recently brushing up on some FIR filter design and was browsing the Wikipedia page. A claim in the article caught my attention: The main disadvantage of FIR filters is that considerably more ...
1
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1answer
212 views

Design a FIR filter with a Kaiser window

Here is the exercise I am working on. Use the window design method with the Kaiser window to design a linear phase high pass FIR filter of minimum order that meets the following specification: $\...
1
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1answer
141 views

Non-separable, higher-order generalized cosine windows in 2D for images

Higher-order generalized cosine windows define a useful parametric family of windows functions, embedding Hamming, Hann, Blackman, Nutall, etc.: $$w(n) = \sum_{k = 0}^{K} a_k\; \cos\left( \frac{2 \pi ...
1
vote
2answers
634 views

Hilbert transform with a sliding window

I have a input voltage signal which has disturbances present in it. I am actually discretizing the input signal into say $1300$ samples and taking Hilbert transform of the signal by taking $N$ samples ...
1
vote
1answer
50 views

Should zero element be considered to calculate mean when smoothing spectrogram by window?

My (mass spectrometry) spectrogram does not measure the intensity constantly. I obtain the spectrogram, for example, ...
1
vote
1answer
115 views

Why does my plot of the Blackman window not match everyone else's in literature?

I've seen the plot for Blackman window as so in a bunch of books, as on this website: But plotting the same equation on Wolfram Alpha yields a different plot: Why is their graph not centered around ...
1
vote
1answer
305 views

How is the ends of a bandpass filtered signal reliable after applying the cosine taper?

A taper function decaying to zero at ends such as a cosine window is routinely applied to the signal before bandpass filtering to reduce end effects. Obviously the window alters the waveform. So, as ...
1
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2answers
401 views

Instantaneous magnitude

I was reading this thread: How to get Instantaneous Magnitude for a Instantaneous Frequency From FFT? I have basically the same question, but I'm curious about more detail about the Hann window ...
1
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1answer
844 views

Additional prefix and suffix required when windowing an OFDM symbol?

To reduce out of band energy, it is common to apply a Raised Cosine filter to the front and back of an OFDM symbol. It is also common to overlap the windowed portions of adjacent symbols to eliminate ...
1
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1answer
1k views

Inverse the Hanning Window [closed]

I am using the following formula to calculate the Hann values for a set of points: $$ w(n)=0.5\left(1-\cos\left(2\pi \frac nN\right)\right) $$ To implement this in java, I am using the following code:...
1
vote
1answer
167 views

Why do we not use square filters without windows? [duplicate]

This question may sound like "why do we use window functions", but it's not. So here it's: What we currently do: If we have a function $g(t)$ and its Fourier transform $G(f)$, and a window $W(f)$ and ...
1
vote
1answer
841 views

How to Combine FFT Overlap Results?

We currently have C/C++ FFT code with Hann Window function support. For a large data (over 10,000) we want to split this into 1024 samples with 50% overlap. For each 1024 sample, we window and fft. ...
1
vote
2answers
54 views

Multi Resolution STFT for audio

I am looking at trying to achieve a multi resolution STFT analysis on a log sine sweep audio measurement. I have an impulse, and I would like to perform two different windowed length FFTs on the ...
1
vote
2answers
84 views

Multiple different length Windows for high resolution realtime FFT

I am looking at trying to achieve a 'realtime' (as quick as possible to acquire, process and present data) FFT application to analyse audio. I have setup my app to acquire a set of samples, apply a ...
1
vote
1answer
479 views

How to design a lowpass filter using Hamming window and sinc function

I have these three equations and have a noisy voice signal. I have to design a low pass filter of length N=1000 using hamming window technique. I have selected its cutoff frequecny 0.25 (normalized). \...
1
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0answers
127 views

Windowing a signal by using Hanning / Hamming or… zero padding?

My question is about the use of Hanning or Hamming windows versus "square" windows. In my understanding, I will use a Hanning or Hamming window to limit the spectral leakage. But, on the second hand, ...
1
vote
2answers
288 views

Short length windowed sinc filter

I have a 50-60Hz signal being sampled at a frequency of 25 kHz & I'm trying to filter all frequencies beyond 70 Hz with a reasonable steep transition band (approx 4 Hz) & good attenuation (~40+...
1
vote
1answer
300 views

Is information lost due to Hanning window perturbations?

I apologize for the obscure phrasing of the title of the post...My question is quite simple... Let us imagine an audio signal (any song will do). We want to apply the Short Time Fourier Transform ...
1
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0answers
28 views

Where can I find more information about this formula relating a window's time and frequency size?

I remember having seen a formula of the form $C=\frac{B}{L}$ that relates a duration $L$(s) of a window to its width $C$(Hz) in the spectrum (defined at -3dB or so). The constant $B$ would be ...
0
votes
2answers
643 views

Why are window functions used when calculating spectral estimates, really?

Having just read the rather long article on Wikipedia about window functions, I still do not see the mathematical point in using window functions when calculating spectral estimates (using e.g. Welch'...
0
votes
2answers
540 views

What is a “square window function”?

When I read previous studies it mentioned a method of "square windowing function". I searched but I did not find anything talking about it. Can someone help to explain what is "square windowing ...
0
votes
1answer
48 views

What does the 'B' parameter represent in Wikipedia's page on window functions?

I was trying to learn some more window functions and was referencing the Wikipedia article on the subject. I've noticed on a lot of the plots, there appears to be a capitalized and italicized letter B....
0
votes
2answers
250 views

Interpolated FIR filter group delay

I'm trying to design a digital low pass filter with a narrow transition band. My sampling rate is 25 kHz, the cut off frequency is 60 Hz & the transition band width is 4 Hz. I'm looking for about ...
0
votes
1answer
1k views

Overlap and windowing a signal for signal processing

I’d like to digitally signal process an audio data. Therefore my idea was to: Split the audio data into individual blocks of 16 samples each. Each block has an overlap of 50% (8 samples are shared ...
0
votes
1answer
409 views

MRI reconstruction using windowing based apodization

I am trying to apply windowing to do MRI reconstruction. I have a 256 point one dimensional k-space samples which look as follows: Here, the real part(green) is flat around 0 and the blue curve is ...
0
votes
1answer
581 views

Why does the Hamming window attenuate the FFT?

I am working on a very simple voice recognition system using the msp430. In my research I've read that for real life audio signals its necessary to apply a window to the FFT data because the audio ...
0
votes
2answers
85 views

Half Window Functions and Formulas

I am looking at implementing different window functions in an application I am making. I have found the formulas for all major symmetrical windows, however I would like to implement half windows. ...
0
votes
1answer
44 views

How to deal with overlap in STFT when considering the highest energy among multiple channels

I have a 4 channels audio file. As a pre-processing step, it goes through an STFT with $T$ frames and $M$ frequencies. The output is divided into magnitude and phase per channel, so for $C$ channels, ...
0
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2answers
36 views

Frequency Resolution Problem

Im trying to tackle the following problem while still not having a firm idea on what "frequency resolution" means : Suppose we sample a continuous time signal with sampling period Ts = 1/2000, and ...
0
votes
1answer
240 views

fft - spectral leakage from noise into target frequency?

I have an acoustic setup. A sender, emitting a clean sine signal. The receiver is far away. In the time domain, the sine is hardly visible because the noise is nearly as big as the signal. In the ...
0
votes
1answer
451 views

Integer and a half periods of sine wave in DFT window

Why does a pure sine wave starting and ending at 0 in the sample window of a DFT but containing 1.5 cycles (or periods) produce the same spectral leakage (i.e. not more) as a pure sine wave with ...
0
votes
2answers
1k views

finding the fundamental frequency in frequency domain

I want to get the fundamental frequency of a signal. I used a time domain approach first. It just sums up the differences between the signal (lets say 2048 samples) and the delayed version of the same ...
0
votes
1answer
127 views

Sensitiviy and Resolution in Windowing Functions

When I read the article Windowing Functions, there are two terms that are does not understanding them well, sensitiviy and resolution. I looked for this two terms on the web, And I conclude that ...
0
votes
1answer
99 views

Subsampling data: terminology

I'm writing software and the data reporting frequency is slower than the acquisition cycle, so effectively sub-sampling is being done. Different data types require different methods of sub-sampling ...