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Questions tagged [lowpass-filter]

A low-pass filter is an electronic filter that passes low-frequency signals but attenuates signals with frequencies higher than the cutoff frequency.

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2answers
180 views

How can you intutively figure what the impulse response will behave like?

I was trying to understand convolution from this book and came across this figure: Here, the input signal is a combination of a sine wave and a ramp. In fig a, the input signal is convolved with a ...
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9k views

FIR vs IIR filter

In my filter design, FIR gives order 14 and IIR gives order 8 or 4. so what are the disadvantages of IIR design?
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1answer
346 views

Time-averaging as a low-pass filter?

I run into the following filter that is supposed to do some type of time averaging of $x$ $$y[n]=G\cdot y[n-1]+(1-G)\cdot\dfrac{x[n]-x[n-1]}{T} $$ where $$G=e^{-2\pi c T} $$ $T$ is a time interval,...
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198 views

How to pad a windowed sinc filter in the frequency domain

I'm creating windowed sinc filters to apply them to certain signals that I'm dealing with. To design the filters, I'm using the approach described in the book "The Scientist and Engineer's Guide to ...
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1answer
418 views

Discrete algorithm for low pass filter

I am working on a position controller for a marine vessel. I have an measurement signal containing the y-position of the vessel that consists of both low frequency (<.1 rad/s) and high frequency (>....
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3answers
2k views

Appying a Filter Several Times on Data

I have data from an experiment and apply a lowpass filter (digital Butterworth filter, in Matlab). My question ist what happens if I apply the same filter e. g. 2 times on the data? What is ...
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0answers
146 views

Multiply filter kernel by sine

1)Suppose that we have low-pass filter with cf equal to 0.1. How frequency response would look like if I multiply filter kernel by sine with frequency say 0.3? How this is related to converting low-...
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1answer
2k views

correct for shift from butterworth filter?

I have implemented a python butterworth filter but it seems to shift the data a lot, the x location of my data is very important to me for my analysis. Is there a way to correct for this shift ...
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1answer
4k views

How to calculate the time delay of a signal by a first-order filter

lets assume following signal $$x=a_1 \sin(2\pi f_1 t) + a_2 \sin(2\pi f_2 t).$$ This is passed through a simple single-pole filter with cut-off frequency $f_c$. How is $x$ delayed by the filter (peak ...
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2answers
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Audio signal processing

I am trying to code audio signal processing software in java. Purpose: It will use audio signal processing library to filter out noise from the raw PCM based input (.wav) of heartbeat recording. ...
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1answer
253 views

Low pass filter to maintain edge information

I am looking for a kernel acting as a low pass filter that satisfies these conditions: $$K(-\mathbf{u})=K(\mathbf{u}) \tag{1}$$ $$K(\mathbf{u}) \ge K(\mathbf{v}), \;\; \text{if} \;\; |\mathbf{u}|<|...
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1answer
884 views

Simulation and theory of first-order low pass filter

I am trying to teach myself some signal processing and control theory. I'm currently working through THIS tutorial. I've started an ipython notebook to keep my notes in. Unfortunately, something is ...
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2answers
2k views

Low-pass vs median filter delay

I need to design a filter to reduce noise from accelerometer readings and use this data to a control system. One of the problems of a simple low-pass filter (like a single pole IIR filter) is the ...
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1answer
146 views

Designing the filtering for a time domain data acquisition application

I want to filter sensor signals for a data acquisition application on an ATmega microcontroller. The interesting parts of the signal are in the range 0-5Hz, and I'd like to leave these mostly ...
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1answer
2k views

once again,confusion between phase and group delay [duplicate]

Despite,reading up on this I'm unable to find crystal clear clarity on the differences b/w phase and grpdelay functions and interpretation of grpdelay's output. I have designed a low pass butterworth ...
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1answer
180 views

Understanding IIR , Low Pass, High Pass, Chebyshev, Elliptic Filter? [closed]

I see these terms everyday in every lecture, I do read stuff from wikipedia, follow lecture notes, study solved exercises. All in all I do have a rough idea about these, I know a little from ...
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1answer
286 views

How to filter uniform noise in a microcontroller?

By uniform noise I mean a band of a fixed width, no spikes, etc. This has to be one of the simplest examples. I'm looking for the appropriate theoretical approach as much as something relatively ...
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1answer
735 views

First-order low pass filter with bounded derivative

Given a function $x(t)$ and a first order low-pass filter $\frac{dy}{dt} = \frac{1}{\alpha} (x(t) - y(t))$, is there a way to choose $\alpha$ analytically such that the derivative of $y(t)$ is bounded,...
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0answers
526 views

Calculate cutoff frequency of filtered data

I am processing data which was put through a low pass filter at some point. Looking at the FFT, I can see that it is less than the Nyquist rate. I am trying to filter another set of data so that the ...
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1answer
366 views

What is a low-pass filter for a sequence of tuples?

I am currently reading SEGMENTATION AND RECOGNITION OF SYMBOLS WITHIN HANDWRITTEN MATHEMATICAL EXPRESSIONS. There is one sentence I don't understand: The preprocessing stage is subdivided into ...
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1answer
338 views

Implementations of Low-Pass Filter

I should say which of the filters from the following image implements an ideal low-pass filter with cutoff frequency $\frac{\pi}{4}$. In the picture, Sa is a zero insertion filter, which inserts a ...
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2answers
517 views

Audio distortion while implementing a low-pass filter

I attempted to implement a real-time audio filtering in a callback function using the simplest moving-average filter with coefficients [0.5 0.5] : ...
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1answer
148 views

How to remove historical values from exponential filter

Suppose I have two time series $A:=[0,0,0,4,5,6]$ and $B:=[1,2,3,4,5,6]$. I implement the following filter (with initial value at the first element): $$ f(t) = f(t-1) + \alpha*(f(t)-f(t-1))$$ with $\...
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768 views

How to set the frequency cut-off for a low pass RC filter?

How do I set the frequency for a low pass filter illustrated below?
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2answers
10k views

Difference Between Equiripple & Least Squares Design for FIR Digital Filters

For an efficient and optimized digital FIR filter design, there are two methods available broadly, Equiripple filter design & Least Squares filter design. A general method for designing a filter ...
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653 views

Types of Filters

Which filters response is maximally flat at origin? It seems to me that both High Pass Filter and Band Pass Filter have maximum flat response at origin, although it is almost zero in case of Bandpass ...
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Statistics of the output of a high bitrate signal filtered through a narrow band low pass filter

I was wondering what would be the statistics of the output of the filtering of an extremely wideband signal (e.g. 10 Gbps random data stream) through a narrowband low-pass filter (e.g. 10 MHz LP). I ...
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1answer
473 views

Is it necessary to taper two ends before fft a time series?

I saw in some codes people always taper the ends of a signal using a cosine taper. Is that necessary and why?
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1answer
509 views

Filtering discrete data

Is is possible to use a digital filter (eg. Butterworth) for smoothing sensor data that is sampled at a non-constant rate? The time between two consecutive samples is between 12 to 40 ms.
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2answers
3k views

When lowpass filtering with a Gaussian kernel, how can $\sigma$ be related to cycles/pixel?

I wish to low pass filter an image with a Gaussian kernel. However, I also wish to select a filter that has the property of producing images that have have no greater than N cycles/pixel. Let's say I ...
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4answers
2k views

Digital Anti Aliasing Filter For Waveform Band Limiting

I am working on some waveform generation software and I am trying to figure out what the best type of filter would be to use a an Anti Aliasing filter for my algorithm. I am generating my waves in a "...
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1answer
177 views

Drawing in images

I want to develop a procedure to remove some inpainted text from images, i.e. I have to estimate the inpainted pixels. I will do that with first an imputation step and then applying SVD (and perhaps ...
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2answers
9k views

Savitzky-Golay filter parameters

I am trying to smooth a series of data in order to obtain a continuous function that could represent that given data set. It came out that the Savitzky-Golay method could be a good way. Now, I don't ...
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0answers
767 views

Lowpass then Inverse filtering in python

I wrote a simple lowpass filter in python to run against lena. Now I'd like to add Gaussian noise to the lowpass filtered data and then run an inverse filter against the lowpass and try to get the ...
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3answers
475 views

Integer upsampling - leave original samples unaltered

I'm looking at the problem of integer upsampling (i.e. interpolation). This can be achieved by first increasing the sample rate by factor $L$ (i.e. inserting $L-1$ zeros between the original samples) ...
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4answers
715 views

Is there an algorithm for second order filtering of data where the filter frequency is not known a priori?

It is well known that a moving average algorithm done in the time domain is equivalent to a filter with frequency response $\mathrm{sinc}(\omega\tau)$ where $\tau$ is the averaging time. (see this ...
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1answer
169 views

Malaysia Flight 370 Image Processing

I wish that all those people on that flight were with us, and maybe they still are, as I like to think they are on an island somewhere waiting to us to find them ... however, it does not look good... ...
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Why does the inverse fourier transform of a lowpass filter have complex components in matlab?

I am quite confused whether the following numerical differences i find are just severe round off errors made by matlab, or something i am doing wrong. The following happened when trying to see what a ...
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2answers
638 views

Intro Question to Signal Processing (Low-Pass Filter)

I have a noisy signal file in Matlab and I have to denoise the polluted signal using a discrete Fourier transform. I'm asked to perform the fourier transform, then take its absolute value. Then study/...
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5answers
4k views

How to separate a low amplitude signal of same frequency but different phase

I have a signal consisting of two sine waves of same frequency but have different phase (and also a lot of HF noise). Their amplitudes differ by about $120\textrm{ dB}$. How to I go about separating ...
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1answer
2k views

Oversampling in OFDM

Why do we need an oversampling in OFDM signal? and how to do it? If around half of the Sub-carriers are only used to send data, then do we need to perform oversampling to the signal? Is it necessary ...
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2answers
7k views

How to use low pass filter in Matlab for discrete data? [closed]

As see in the picture, there are high frequency noise in the signal. How to design a low-pass filter to eliminate the noise? How to apply this filter in Matlab?
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Low pass butterworth filter is distorting [duplicate]

my low pass filter keeps distorting and I'm at a loss to explain why. It calculates the correct coefficients, but distorts everything. The code is as follows. It's driving me mad. What's weird is my ...
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1answer
155 views

A question on filters

I am fairly new to DSP have been reading up on digital filters and have a few questions. I have a signal with very high frequencies whose DC component i want to estimate. The magnitudes of these ...
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1answer
518 views

Analytical Calculation of the Impulse Response of an Arbitrary Filter

This is a rather general question. Suppose I have an arbitrary filter, $F$, defined in the Laplace domain; $$ F=k\frac{\prod_i (s+z_i)}{\prod_j(s+p_j)}. $$ How do I calculate the impulse response of ...
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2answers
216 views

What are the values on the x-axis when I plot the impulse response of a lowpass filter?

I am trying to develop a filtering routine, using Java, and I am using the windowing method. From my studies, I was told that if I make a plot of the impulse response of an ideal lowpass filter, I ...
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3answers
209 views

Low analog lowpass + ADC vs High analog lowpass + ADC + low digital lowpass

I'm doing EEG data collection and my amp forces use of an analog lowpass filter before the ADC. I'm fairly sure that I won't be interested in phenomena associated with frequencies of 30Hz or higher, ...
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2answers
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Doing resampling, how can we choose lower cutoff frequency for LPF filter?

I would like to resample an audio signal. Sampling frequency of an original audio signal is 50k Hz. What I want to down sampling frequency is 30k Hz. In this case, I followed the procedures as ...
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2answers
10k views

Algorithm for implementing an IIR digital filter, Chebyshev type I low pass

I am trying to implement a Chebyshev type I low-pass IIR digital filter in C. I have got the SOS Matrix and scale values from Matlab. What is the direct equation or algorithm to implement such a ...
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1answer
2k views

Realisation of a passive RC low pass filter

I have an unusual low-pass filter problem that I would like to realise with a passive RC network (Note 1). It's easy enough to find prototype filters for passive RLC networks, or for the various ...