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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331 views

Why is the lowpass-filter coming right after the local oscillator when mixing an RF?

In the book, instead of having a band- or lowpass-filter before mixing, it's coming right after mixing, which makes sense, considering there's gonna be a high-frequency component, which has to be ...
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245 views

Frequency response of $\mathrm{sinc}[n]$

In this image the frequency response of a discrete time filter given as $h[n]$. Can someone explain how the magnitude of the frequency response is found ?
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What happens, when an unlimited bandpass-signal gets mixed?

In theoretical books there's always a bandpass-limited signal being mixed, that's been low-pass filtered beforehand. But what happens, if the RF-signal from the antenna isn't band- or lowpass-...
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4answers
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Effect of low pass filter on the time domain

Consider an ideal (rectangular profile in frequency domain) low-pass filter (LPF) which simply sets to zero all the frequencies beyond a certain cut-off frequency. Let $x$ be a discrete-time signal of ...
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461 views

Shannon interpolation formula for downsampled data with an “almost ideal” low pass filter

Let $x[n]$ be a discrete time signal with DFT given by $X(f)=\sum_n x[n]e^{-2\pi inf}$ supported on $[-1/2M,1/2M]$ with $f\in[-1/2,1/2]$. I can then down-sample to get $y[n]:=x[nM]$. Then, let $$\...
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1answer
418 views

ifft doesn't recreate original signal

I want to convert given signal into frequency domain and do some calculation and then convert that signal into time domain. Here is the code which I am trying out ...
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2answers
3k views

How to apply low-pass filter to an I/Q signal to get baseband signal?

Can anyone help me with the demodulation technique of a modulated signal? I mixed it with I/Q signal. But I am very confused about low-pass filtering. I am trying to apply a low-pass filter, but I am ...
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3answers
160 views

Odd problem with really long sinc filters

I'm trying to build a "perfect" low-pass filter as an exercise to test that I've understood some basics in signal processing. I've computed the required length of a sinc function such that at either ...
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1answer
346 views

How to design a FIR low pass filter and force a subset of filter coefficients to 0?

I'm looking into interpolating a signal by 2x and came into this matlab function interp: interp Interpolation — increase sampling rate by integer factor ...
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1answer
531 views

RMS of absolute-valued sinusoid

A signal $x(t)=|\sin(2π(1000)t)|$ ($|x|$ is the absolute value function) is fed to an ideal low-pass filter with cutoff frequency of 1500Hz to produce an output $y(t)$, what is the RMS voltage of $y(t)...
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Obtain the complex envelope of a two-tone signal

I know it is possible to represent a single-tone signal by its complex envelope: \begin{align} x(t) &= A(t)\cos(2\pi f_c t + \Phi(t))\\ x(t) &= \operatorname{Re}\left\{A(t)\mathrm{e}^{j \Phi(...
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Understanding audio downsampling code (JavaScript) and adapting to a different ratio

I inherited responsibility for some audio downsampling code that I don't fully understand: ...
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976 views

Discrete Time Fourier Transform (DTFT) for an unstable system (Ideal Low Pass Filter)

The Dirchlet conditions state that if the signal is absolutely summable then it the DTFT of the signal definitely exists. This is a sufficient condition but not necessary condition. There are ...
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1answer
69 views

Does a filter need to completely attenuate high frequencies to be considered low-pass?

I'm looking at a system with a frequency response that is: $$H(e^{j\omega})=\tfrac{1}{4}(2\cos(\omega)+\cos(2\omega)+2)$$ I think the magnitude of this system looks like this (not sure what is the ...
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Appropriate digital filter for GPS tracks?

I have an open-source software project whose purpose is to analyze a GPS track, or a similar track made by an application such as google maps, and estimate the physical exertion required to hike or ...
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1answer
380 views

Eye Diagram of QPSK Modulated Signal

I need to plot eye diagram for RRC filtered QPSK modulated signal. The specifications are given as follows Sampling frequency : $1.024$ MHz Symbol Rate : $256$ Kbps (Hence, Upsampling rate = $4$) ...
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54 views

Locate first minima in signal

I have many datasets which all looks roughly like this: All the datasets have this in common. First there is an artifact around 0 with an unknown (but likely very high) intensity. Then there is some ...
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1answer
273 views

DSP filter. Is prewarping performed when discretizing using Forward/Backward?

I am trying to derive the coefficients used for a IIR implementation for the lowpass portion of a SVF filter. I've seen finished expressions for the coefficients (smith (p.8) and victor), their ...
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1answer
243 views

Filtering everything outside 20 - 20000 Hz

With an audio .wav file (sampled at 44.1 or 96 Khz), I would like to filter out everything outside the 20 - 20000 Hz range. I tried a Butterworth bandpass filter and there were unstability issues, ...
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1answer
374 views

python rewrite lfilter (iir) with for

It's a beginner question, but useful to users from python - signal.lfilter, I was using lfilter from Find reverse one pole ...
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2answers
445 views

Find reverse one pole lowpass filter

I need to find a filter that revert the one pole filter of the current signal, a function using Python (or MATLAB) scipy.signal.filtfilt or ...
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2answers
530 views

What is the name of these simple filter algorithms?

I found some snippets of code on the internet that are really simple signal filters. Unfortunately there wasn't much info to back it up. Using Google I've found similar code, but none of it backed up ...
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505 views

How to implement a time-varying filter?

I'm working on a 10-second sound, sampled at 44.1 khz. I want to do filtering, and have a desired EQ (equalization) curve that varies over time, as suggested here (here $f0=250\ Hz$) How to ...
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1answer
338 views

OFDM Transmitter knowledge

I have some questions regarding some concepts used in designing the OFDM transmitter which i got from different literature reviews but i got mixed up with these concepts. • The N-Ifft points and ...
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1answer
302 views

Low-pass filtering bounces when signal doesn't start at 0

Say I have an array representing a signal, going from 30 to -30 in 1000 increments, with a little bit of noise on those values. If I apply any king of low pass filtering (Besset, Butterworth, Savitsky-...
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1answer
101 views

How to interpret these filter coefficients?

I am trying to make sense of the filter coefficients. The author claims that they are running a 3rd order lowpass Butterworth filter and were willing to give their design. They are not the most ...
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1answer
4k views

How to convert a low-pass Gaussian filter to a high pass filter

I have the following code for a applying a Gaussian filter to an image. From what I understand this is a low pass filter. Now I have to convert this into a high-pass filter, and from what we were told ...
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2answers
2k views

Definition of Ideal Low pass filter (Time Continous)

Actually I got confused about definition of frequency response of Ideal low-pass filters because in some books they mention that phase of H(f) should be linear in pass band and it's value is $ -2\pi ...
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2answers
676 views

Is it normal that a DAC outputs spikes?

I'm using a Raspberry Pi 2 and an AD/DA Board, with no extra circuit. Reading on the internet though, I found that DACs need a low pass filter in their output, and I don't understand if the behaviour ...
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2answers
400 views

Effect of window function on audio output

If I have a low pass filter, does the choice of window function I use have any effect on the quality of the audio input? What would be the effective difference between using a rectangular window and a ...
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1answer
138 views

$Q$ factor refers to what on a lowpass filter? (EE kind of definition)

For what I'm learning, the bandwidth (of a BPF, for example) refers to the $\Delta$ between $f_L$ and $f_H$ at (usually) $-3\textrm{ db}$ from the $f_0$ (from wiki). For a peaking filter instead, $f_L$...
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Why analog anti aliasing filter is used before analog to digital converter when there is already a digital filter after ADC?

Normal data acquisition consist of: Analog anti aliasing filter( Sampling frequency : $5\textrm{ kHz}$) ADC - Digital Filter - (Sampling : 200K samples /sec) Digital low pass filters Filters DAC ...
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3answers
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What is the intuition of “averaging is a low pass filter”?

As I know, the shape of a low pass filter in time and frequency are as follow: But how averaging work like a normal function in time domain? Is there any intuition in it?
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Velocity estimation from distance sensor

I know it is a generic question but I did not find a specific answer to it online. My question is: I have a range sensor based on the time of flight (Infrared Sensor. Transmitter-Reflector-Receiver)....
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0answers
175 views

Two way Audio crossover MATLAB code using Bessel

Could MATLAB's besself function be used in designing an Audio crossover (Tweeter and Woofer) with highpass and lowpass filters? Most likely the same with this ...
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1answer
445 views

How to design and implement a low-pass AR1 filter in Matlab?

I have a data series y(n) that I want to filter using a low-pass AR1 filter. I found that this filter has a transfer function ...
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1answer
1k views

Detecting Zero Crossing in Image Filtered by Laplacian Operator

This is my first question on this site, complete noob. But here goes. I have a positive Laplacian operator [[0,1,0], [1,-4,1], [0,1,0]] Now this Laplacian ...
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1answer
2k views

Cutoff frequency of a first order recursive filter

I've implemented a very simple first order recursive low pass filter in c using the algorithm: ...
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2answers
1k views

Resampling an audio signal

I am trying to resample an audio signal in my application. It will be between 48kHz and 96kHz audio (both upsampling and downsampling). Looking at the Wikipedia page for resampling I see there are ...
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3answers
617 views

FIR analog low-pass filter?

Is there a way to construct FIR analog low-pass filter? (By this, I believe I am asking for no-pole analog low-pass filter, in terms of Laplace transform.)
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81 views

Optimizing Two Parallel IIR Filter Sweeps

Got an audio related question here; So I have two IIR low pass filters that work in parallel to do a filter sweep. Basically: ...
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1answer
232 views

Beginner's question on LPF, Need for Sinc and windowing [duplicate]

As a student who has never constructed any real world DSP application, I am inclined to ask the following. Convolution in time domain is multiplication in frequency domain. For low pass filtering, ...
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1answer
2k views

Cancel Drift after numerical integration

I am trying to integrate angular acceleration obtained from a set of accelerometers positioned specifically at opposite corners of a cube, based on the paper EcoIMU: A Dual Triaxial-Accelerometer ...
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1answer
430 views

Kalman filter after lowpass filter: bad idea?

I am new to Kalman filter and am enjoying playing with it. However, I generated some random velocities and acceleration and Kalman filter (with the covariance matrices I have chosen) is comparable ...
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1answer
1k views

Interpolation filter gain

If somebody could clarify why everywhere is written that the interpolation filter should have gain $L$ where $L$ is upsampling factor. What this gain actually means? Does it compensates for the ...
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1answer
2k views

Does lowpass filtering and decimating improve SNR?

I did not manage to find clear answers to this question: does decimation after an appropriate lowpass filter improve the signal to noise ratio? To investigate this question, I considered data ...
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1answer
229 views

How to get rid of ripples from a gradient image of a smoothed image?

I have a gray scale uint8 image. When I smooth it with a Gaussian filter and then compute the gradient image with a Sobel filter in OpenCV, ripples would appear. The first image is what happens when ...
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1answer
371 views

Sampling the impulse response

Given two IIR filters (one Low-Pass and one High-Pass) designed using Butterworth, how can I know if they can be obtained using sampling the impulse response?
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255 views

Making a low pass filter for irregular samples

We are interested in reconstructing the red channel of a scene. The red channel is slowly varying. Unfortunately the camera does not have a Bayer sensor, and the red samples are irregularly spaced ...
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1answer
145 views

Output of lowpass filter with damped sine wave input

The random process $$Y(t)=\cos(\omega_0t)\cos(\omega_0t+\pi N(t))$$where $N(t)$ is a Poisson process of parameter $\lambda$ enters a lowpass filter with transfer function $$H(j\omega) = \left\{ \...