A low-pass filter is an electronic filter that passes low-frequency signals but attenuates signals with frequencies higher than the cutoff frequency.
3
votes
1answer
58 views
Implementation of basic 2-pole low-pass filter
I know this question has been asked to hell and back from many people, and that it will probably get downvoted until it's deleted, but please bear with me.
I am designing a sound engine for one of my ...
2
votes
2answers
154 views
Even after applying a low pass filter, why is there a DC offset?
I need to smooth some data segments and one of the techniques I am experimenting is a low-pass filter. So I designed a low-pass filter in matlab and applied it to my signals. Here is what happened ...
0
votes
0answers
55 views
How do decide which order my butterworth filter should have?
I have a signal that was recorded with around 300 samples in a second. Now I want to run a low pass and a high pass butterworth filter over it. The frequency for the high pass filter is around 0.05 Hz ...
3
votes
1answer
81 views
Interpolated FIR filter
I am confused about this Q&A : Interpolation by factor of 2
If my input signal
$$
x[n]= x0,x1,x2,x3
$$
then according to the threads explaination my $v[n]$ will be
$$
v[n]=x0,0,x1,0,x2,0,x3,0
...
4
votes
3answers
78 views
Low pass fir filter
In my filter specs, the passband gain is given as 6.02db. How to achiece this?
Usually all texts has given passband gain as 0db(and passband ripples if any).
2
votes
3answers
94 views
Interpolation by factor of 2
I want to up-sample my input signal by a factor of 2. I saw zero padding followed by Low Pass Filter method being used in few cases. But still i need some help in this. Say i have 10 input samples and ...
1
vote
3answers
184 views
How does a low-pass filter programmatically work?
I have been working on a simple low pass filter for < 100 Hz metering in my application. But so far, I am struggling with the theory behind it all. It's cool that I got it working, but I'd really ...
4
votes
2answers
118 views
Low Pass Filter Artifacts
I have created a Low Pass filter (I am trying to understand the topic of DSP, and it's hard.. But moving along with samples, books and a nice post on Stack Overflow).
I am saving the 'output' to a ...
1
vote
1answer
73 views
Approximation using a Fourier transform with low pass filter
I need to approximate a function f, but I cannot do so with frequencies that exceed 1kHz
What is the best approximation I can get? Is taking the Fourier transform then zeroing any term above 1kHz the ...
1
vote
2answers
106 views
Strange noises when filtering audio signal
I am using Naudio open source library and I am trying to do some simple filtering. The problem is that I hear some "clicks", not too loud. The library offers me the possibility to use at least two ...
0
votes
2answers
108 views
Memory of a filter used on real time digital signal processing
My question is regarding the memory of a filter when we want to implement it on a real time dsp environment. We have certain memories like scratch memory , intermediate memory and internal memory. ...
1
vote
2answers
90 views
filter for reducing background noise in image
I have images where there is a lot of "black" background (few shades of black). (In many images at least half the pixels are background). I need to get interest points from the image, but because the ...
0
votes
1answer
80 views
Downsampling and Gradient filtering
Are the following sequence of operations the same -
Down-sampling filtering followed by gradient filtering with kernel [-1 0 1]
Gradient filtering with kernel [-1 0 1] followed by down-sampling
...
1
vote
1answer
132 views
Is a DC signal 0 frequency or extremely high?
If I pass a signal with DC component through a Low Pass Filter will the output be without the DC component?
5
votes
1answer
133 views
Filter message from noisy voice signal
I am trying to decipher a message hidden within a very noisy audio file(.wav)(I think it is white noise with an additional low drone). The message is a six digit number. I have not have any further ...
3
votes
2answers
835 views
A Simple Lowpass Filter Behaving so Strangely
I don't know much about filter design. After reading a few articles on wikipedia I am playing with filter design and I see something weird and would like some help in understanding what exactly is ...
3
votes
1answer
232 views
Ideal Low-Pass Filter Output?
I'm very new to digital signal processing, I've been reading a text book to try to figure out this assignment at work (avionics related). I'm supposed to implement a two-pole low-pass filter with a ...
3
votes
1answer
155 views
Equivalent 2D mask of moving-average
I have the moving-average mask as
mask = [1 1 1; 1 1 1; 1 1 1];
and then I compute the convolution 3 times
...
3
votes
2answers
110 views
Reverse Engineering Bessel LPF (sample frequency needed)
I have the following sourcecode. For all I know, it should be a Bessel LPF at 10Hz. Is there a way to get the sampling frequence out of this?
...
5
votes
1answer
347 views
Choice of Gaussian kernel parameters when lowpass filtering before image resampling?
I need to decimate a signal by a factor of q.
More specifically my signal is a 3D "image": $\ I(x_i,y_j,z_k)$,
which I need to downsample by a factor of two in the z direction.
I want to do lowpass ...
2
votes
1answer
195 views
Best way to resample a signal (image)?
I have an original image $\ I(x_i,y_j)$ where
$\ x_i = i*\Delta x, 0<= i < n_i $
and
$\ y_j = j*\Delta y, 0<= j < n_j$
I am trying to implement a function that resamples the image ...
2
votes
2answers
214 views
When negative frequencies cannot exist in practice, why do we calculate power in negative frequency?
Suppose a signal with two-sided power spectral density $N/2$ is passed through an ideal LPF having cutoff frequncy $B\,\mathrm{Hz}$. The output power is equal to $N/2 \times 2B = NB$ Watts. Why not ...
3
votes
3answers
228 views
LPF and HPF Confusion - Rectangular and Circular Cut-Offs
Interpreting some homework, I'm a little confused on what it's asking for. I'm asked to filter in the frequency domain (easy enough, just a fft2 and ifft2 when I'm done) a 256x256 8bit grayscale tiff ...
1
vote
1answer
180 views
Filtering PCM data in java
I'm working on an audio based application for android platform , I'm trying to use a low pass filter to a fixed or variable max frequency "depends on the cost of development".
first I've been playing ...
3
votes
1answer
125 views
Do lowpass filters affect the integral over the signal?
For which filters, does the resulting signal have the same integral (/average) as the original? Obviously this is true for a moving average, but is it also mathematically true for e.g. a Butterworth ...
4
votes
2answers
246 views
Downsample Equiripple FIR filter
I am designing some Downsampling filters using the remez exchange algorithm (Matlab FDAtool). I see that some times i get a spike at the first and last coefficients. does anybody knows why is that? my ...
4
votes
2answers
177 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 ...
1
vote
1answer
158 views
Apply Low Pass (Smoothing) Filter on a Set of Matrices and Reject Outliers
Given a set of a $ 3 $ by $ 3 $ matrices $ {H}_{i} $.
Each matrix is an Homography matrix.
They are used to stabilize Video Stream.
Yet some of them are outliers which creates "Jumps" in the ...
6
votes
5answers
2k views
How to write lowpass filter for sampled signal in Python?
Sorry for question that may be trivial, but I am new in signal processing, and I didn't find python code with good explanation. So I will be glad to get explanation for dummy :)
I have some signal ...
8
votes
3answers
384 views
How should a moving average handle missing data points?
I'm writing a program that averages the user's weight across different days. I'm planning to use a 5-point moving-average (current day, two before and two after). Sometimes, a data point is missing ...
7
votes
2answers
175 views
complementary IIR filters
I would like a pair of complementary IIR filters (lowpass/highpass). By complementary, I mean, when the output from the two filters is summed, the original signal is recovered. I thought I could build ...
4
votes
3answers
82 views
What is temporal neighborhood?
I read in a paper http://tcts.fpms.ac.be/publications/regpapers/2011/nrmmbgtd_icvs_LNCS.pdf about spatio-temporal filters, which is applied to frames of the videos. I could not understand these terms ...
7
votes
1answer
537 views
Differences between filtering and polynomial regression smoothing?
What are the differences between classical low-pass filtering (with an IIR or FIR), and "smoothing" by localized Nth degree polynomial regression and/or interpolation (in the case of upsampling), ...
7
votes
2answers
429 views
Low pass filtering on short int (16 bit PCM) samples
I am writing software for processing audio given as 16-bit PCM samples. The first stage of the processing involves calculating the energy (or total variation) in a certain frequency range (above a ...
-3
votes
1answer
186 views
Function in the Fourier domain of a low-pass filter
I have to represent a low-pass filter in the Fourier domain having a cut-off frequency of $f_c={3}\ kHz$.
Could all low-pass filters could be represented with this function: ...
5
votes
2answers
206 views
What are the characteristics of a “good” smoothing convolution kernel?
At work we were smoothing a signal by convolving with either
f1=[0.2000 0.2000 0.2000 0.2000 0.2000]
or
...
5
votes
2answers
516 views
How to smooth a signal?
The easiest way to smooth a signal is by moving window average.
A more advanced way is to use a Savitzky-Golay filter.
From wikipedia:
The main advantage of this approach is that it tends to ...
4
votes
2answers
698 views
Designing A Filter Using SPTool In Matlab
I am currently working on learning DSP and for my course we use Matlab. I have been tasked with designing a low-pass filter using SPTool with the following specification:
A Low-Pass Kaiser Window ...
1
vote
1answer
378 views
Low-pass filter for cleaning vocal speech before performing onset detection
I am creating a piece of software that detects when speech starts in an audio recording. Before performing onset detection I would like to remove any noise that may cause any false positives. Which ...
4
votes
1answer
709 views
Filter coefficients for colored noise Voss Algorithm
If I use a generic filter for generating colored noise like pink,brown,white then how do I modify this statement and how do I know what are the coefficients to be used in AR model for different ...
5
votes
1answer
341 views
How to estimate taps required for Parks-McClellan filters
I have some code based on Jake Janovetz's Parks-McClellan (Remez) filter generating code. How can I estimate the number of taps required to build a lowpass filter given requirements for pass band ...
11
votes
1answer
455 views
Why is $y(n) = x(n) + x(n-1)$ a low pass filter?
I have found that this is a simple, but bad lowpass filter:
$$y(n) = x(n) + x(n-1)$$
However, I can't understand why it is a lowpass filter. What is its cutoff frequency?
12
votes
1answer
9k views
low pass filter and FFT for beginners with Python
I am new to signal processing and especially to FFT, hence I am not sure if I am doing the correct thing here and I am a bit confused with the result.
I have a discrete real function (measurement ...
8
votes
2answers
105 views
What is this sinc doing in my LP-turned-HP filter output?
I'm trying to HP-filter a signal by LP-filtering it and subtracting the output from the original filter. To obtain the LP-filtered signal, I backward-forward filtered using a third-order Butterworth ...
10
votes
3answers
598 views
Documentation about filters in general
I already posted this question on StackOverflow. I got a suggestion to go for a better answer here.
To make the question more concise I'm interested in an introduction to digital filters, any ...
9
votes
4answers
683 views
What is the physical interpretation of Lowpass/Highpass filtering?
In Image/Signal processing context we have seen/we know that if there are say 4 samples and if we take an average of those 4 samples, then we say that the result sample is a low pass filtered output ...
13
votes
2answers
815 views
How can I lowpass filter by only reducing peak data?
I have a 2D image, which I want to lowpass filter, with these constraints / quality metrics:
I can not "add" light to the image, so each pixel in the result
should be <= the corresponding pixel ...
