Questions tagged [filters]

In signal processing, a filter is a device or process that transforms a signal by selectively choosing specific frequencies and leaving others with appropriate gain or as it is.

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81
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3answers
24k views

Why is it a bad idea to filter by zeroing out FFT bins?

It's very easy to filter a signal by performing an FFT on it, zeroing out some of the bins, and then performing an IFFT. For instance: ...
4
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1answer
1k views

Compensating Loudspeaker frequency response in an audio signal

I have been working on a project in which I was required to work on the audio signals recorded from the loudspeaker kept in front of a filter. So, to simply explain it: $$\boxed{\rm LoudSpeaker} \...
33
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6answers
54k views

Understanding the Matched Filter

I have a question about matched filtering. Does the matched filter maximise the SNR at the moment of decision only? As far as I understand, if you put, say, NRZ through a matched filter, the SNR ...
16
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2answers
27k views

How do I manually plot the frequency response of a bandpass Butterworth filter in MATLAB without freqz function?

I have code like below that applies a bandpass filter onto a signal. I am quite a noob at DSP and I want to understand what is going on behind the scenes before I proceed. To do this, I want to know ...
16
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3answers
48k views

FIR filter with linear phase, 4 types

I know there are 4 types of FIR filters with linear phase, i.e. constant group delay: (M = length of impulse response) Impulse response symmetrical, M = odd Imp. resp. symmetrical, M = even Imp. resp....
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1answer
163 views

How determine the delay in my signal practically

I am trying to practically determine filter group delay so that I can try to reduce or adjust for it. I have tried all kinds of methods but still can't get the right result. I know that theoretically ...
31
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2answers
30k views

What is the advantage of MATLAB's filtfilt

MATLAB's filtfilt does a forward-backward filtering, i.e., filter, reverse the signal, filter again and then reverse again. Apparently this done to reduce phase ...
21
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3answers
5k views

FIR Filter Design: Window vs Parks McClellan and Least Squares

Are there any advantages to use a window approach over Parks-McClellan (further abbreviated here as PMcC) or Least Squares algorithms for FIR filter design of a low pass filter? Assume with today's ...
4
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1answer
1k views

How does this “simple filter” work?

I'm new to DSP, and I'm using this basic "1-pole LPF" Param Smooth filter which "smooth" param when I change it. The code is pretty simple: ...
26
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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?
24
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2answers
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Applying filter in scipy.signal: Use lfilter or filtfilt?

I saw in a SO thread a suggestion to use filtfilt which performs backwards/forwards filtering instead of lfilter. What is the ...
24
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5answers
16k views

What Is the Best First Order IIR (AR Filter) Approximation to a Moving Average Filter (FIR Filter)?

Assume the following first order IIR Filter: $$ y[n] = \alpha x[n] + (1 - \alpha) y[n - 1] $$ How can I choose the parameter $ \alpha $ s.t. the IIR approximates as good as possible the FIR which is ...
21
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2answers
10k views

How do I interpret the DCT step in the MFCC extraction process?

In most audio processing tasks, one of the most used transformations is MFCC (Mel-frequency cepstral coefficients). I mostly know the math that's behind the MFCC: I understand both the filterbank ...
9
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2answers
12k views

Is a leaky integrator the same thing as a low pass filter?

The equation governing a leaky integrator (according to Wikipedia at least) is $\frac{d\mathcal{O}}{dt} + A\mathcal{O}(t) = \mathcal{I}(t)$. Is a continuous-time leaky integrator thus the same ...
8
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2answers
7k views

Filter Order Rule of Thumb

Is there a rule of thumb for calculating the approximate filter order of a FIR/IIR based on passband vs sample rate? I seem to remember reading about it once in Undergrad. I'd think you could make a ...
12
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3answers
3k views

“Low-pass filter” in non-EE, software API contexts

I am an experienced software engineer and am working on smartphone sensors. I've taken fundamental EE classes in DSP and am trying to apply my knowledge. I believe that I understand convolution, ...
7
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1answer
957 views

Adaptive filtering: Optimum filter length and delay

I'm trying to find the optimum filter length for an Adaptive Filtering, using RLS Algorithm. I'm using this design: So the "error" signal is the signal without noise (and that's the signal that I ...
1
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2answers
901 views

FIR Filter Design - input parameters conversion

I am new to DSP and filter design. I have developed a code in C++ to calculate FIR coefficients using Parks-McClellan algorithm. The inputs to calculations are: Filter type (Low-Pass, High-Pass) ...
44
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5answers
58k views

What is the difference between phase delay and group delay?

I'm studying some DSP and I'm having trouble understanding the difference between phase delay and group delay. It seems to me that they both measure the delay time of sinusoids passed through a ...
24
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4answers
17k views

Peak detection approach

What are the peak detection algorithms in existence? I have noisy data, and I would like to implement peak detection for this data. Data is in reverse, actually I am trying to determine the bottom. ...
17
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6answers
25k views

Why is a linear phase important?

If symmetry conditions are met, FIR filters have a linear phase. This is not true for IIR filters. However, for what applications is it bad to apply filters that do not have this property and what ...
4
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2answers
3k views

How to remove or filter the drift problem in measured Strain signal?

I have the strain signal of a lateral beam of a car measured at sampling rate 1,200Hz from data acquiring system. Even after using temperature compensation in strain gage, we are getting drift. So I ...
9
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3answers
3k views

Shift a signal by fraction of a sample

I have a signal with a sample time of 0.5 micro seconds and I would like to shift this signal by a fraction of the sample time, say by 3 nano seconds. I have read a few online resources about ...
3
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2answers
9k views

Why root raised cosine filter can eliminate intersymbol interference (ISI) ?

My question is kinda silly, I know it. But I cannot understand why root raised cosine filter or raised cosine filter can eliminate ISI. I googled before, but those explanation is not easy for me to ...
2
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1answer
929 views

GPS signal acquisition

I have a set of GPS satellite signal data, the set is 1 ms long and has the information of two satellites (satellite number, code phase and frequency) buried in noise. This data has a carrier ...
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1answer
402 views

Applying Image Filtering (Circular Convolution) in Frequency Domain

To filter an image we can: Use a 3x3, 5x5, 7x7, etc. filter, that is convolve the image and the filter in the space domain. Use a FFT on both the image and the filter, multiply them together in the ...
43
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6answers
46k views

Simplest way of detecting where audio envelopes start and stop

Below is a signal which represents a recording of someone talking. I would like to create a series of smaller audio signals based on this. The idea being to detect when 'important' sound starts and ...
15
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5answers
23k views

Why are FIR filters still stable even though they contain poles?

How come FIR filters are always stable? Since they contain poles, shouldn't they be more affected by stability issues than others?
16
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1answer
21k views

How to Extract High Frequency and Low Frequency Component Using Bilateral Filter?

What does High frequency and low frequency component signify in an image. How to separate out the high frequency as well as low frequency component of an image using Bilateral filter.
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6answers
4k views

Convert a FIR to an equivalent IIR

Is there a way to convert a FIR to an IIR filter with the most similar behavior?
3
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1answer
3k views

Analytically designing a notch-filter for specified frequency 50 Hz

I tried to analytically construct a causal notch filter that stops frequencies at 50Hz and I thought if zeros are more than poles it will be non-causal so I chose equal amount of poles and zeros ...
2
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3answers
1k views

How to design very narrow, sharp lowpass filters - Only DC needed?

I asked exact the same here one year ago: One year ago question I asked this question again here, because after one year, I have learned more about DSP and am thinking ways to improve it. Filter ...
1
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2answers
978 views

Different way to separate a particular frequency from a signal

Let's say I have a signal which is composed of 2Hz,10Hz,17Hz,19Hz and 25Hz discrete time sinusoidal waves and I need to allow only 17Hz component to pass. As far as I know, the standard way to ...
10
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2answers
17k views

What Is the Difference between Difference of Gaussian, Laplace of Gaussian, and Mexican Hat Wavelet?

There are three techniques used in CV that seem very similar to each other, but with subtle differences: Laplacian of Gaussian: $\nabla^2\left[g(x,y,t)\ast f(x,y)\right]$ Difference of Gaussians: $ \...
9
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2answers
750 views

Filtering of streaming audio

Given something like 103 data points ($N=103$), a DFT will give back 103 frequency values. Then to do something like filtering the high frequencies involves setting the high frequency values from the ...
7
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2answers
5k views

Which domain used for denoising additive and multiplicative noises

I want to know what is the difference between additive noise, multiplicative noise.. In what domain these noises are handled to remove? I am interested particularly in image dataset Does different ...
5
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4answers
410 views

Mixed time/frequency domain data

I'm afraid this might be a bit of an elementary question, but I'm afraid I'm a little new to this. I've got a system that measures a frequency spectrum to find resonant frequencies. It does this by ...
3
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2answers
2k views

FFT analysis for Vibration Signal

I am working on balancing an air-spindle. For the unbalance analysis I use an accelerometer (NI device). I have the voltage signal from the accelerometer corresponding to the vibration of spindle at a ...
8
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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:} ...
4
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2answers
703 views

Are SOS structures better for linear phase FIR filters?

I've seen many discussions suggesting that SOS's are often/usually the preferred structure for fixed point hardware filter implementations, since they preserve conjugate pairs, etc., but I've never ...
4
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2answers
6k views

Bandpass filters with python for low frequencies

I have a signal, sampled at 1 kHz, that I would like to analyze in third octave bands. For that purpose I defined Butterworth filters with proportional bandwidth. This works well for higher ...
2
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2answers
1k views

CIC Cascaded Integrator-Comb spectrum

I would like to ask something regarding CICs (Cascaded Integrator-Comb filters) or more particular about the frequency response of it. Assuming that I have as input IQ samples from a signal generator ...
1
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3answers
6k views

What is the advantage of weighted median filter over median filter?

I could not find any proof or comparison of weighted median and median filters. Yes the more occurring pixel contributes much but what should be the criteria of choosing weight function. And any ...
4
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1answer
461 views

Discrete-time Biquad filter: Relation between peak frequency and pole frequency

This question arose from a discussion in the comments to this question and its answer. The author of that question discussed a discrete-time second order filter described by the following difference ...
30
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4answers
29k views

What is the true meaning of a minimum phase system?

What is the true meaning of a minimum phase system? Reading the Wikipedia article and Oppenheim is some help, in that, we understand that for an LTI system, minimum phase means the inverse is causal ...
16
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9answers
22k views

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 ...
21
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4answers
4k views

Fast / Efficient Way to Decompose a Separable integer 2D Filter Coefficients without the SVD

I would like to be able to quickly determine whether a given 2D kernel of integer coefficients is separable into two 1D kernels with integer coefficients. E.g. ...
14
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4answers
14k views

could anybody explains me why IIR filters do not have linear phase?

Please tell me. Also I dont know why phase is linear with FIR filters. I would like quantitative analysis. And why linear phase is not achieved by IIR filters ?
15
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4answers
7k views

How to extract traffic signs from a photograph?

What image analysis techniques can I use to extract the traffic signs from an image such as the one below? Edit: After Anisotropic diffusion: The background that i don't want gets cleared a little ...
15
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2answers
6k views

Which IIR filters approximate a Gaussian filter?

So it recently dawned on me that Bessel filters, despite being listed along with the other common types, are really an oddball that belongs in a different "class", and I'm trying to learn more about ...

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