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.

4
votes
1answer
2k views

Lowpass : What is wrong with average filtering?

The question is : What is wrong with averaging as low pass filter ? The details : I want to lowpass filter a signal to downsample it. The constraints are : I have no RAM available and I work in ...
0
votes
1answer
1k views

Downconverting real signal to IQ baseband

Despite reading various answers on this site and on other sites I am still confused about how to convert a real-valued signal back down to its original IQ baseband values. Note I am still a beginner ...
7
votes
3answers
7k views

First order low pass filter

I am trying to better understand the first-order low pass filter: Summary: Per wikipedia, a first order low pass filter yields the following in discrete time: $$ \frac{Y(s)}{U(s)}= \frac{\omega_{c}}...
0
votes
1answer
384 views

FIR filter digital differentiator with low cutoff

I'm trying to design a digital differentiator FIR Filter. It features a lowpass, such that above the cutoff frequency the amplification is very low. I get the coefficients by a linear program ...
0
votes
1answer
79 views

Can I implement a LP filter using DMA?

This questions seems to be a little strange but bear with me. I have an application that needs a digital filter to be implemented in a microcontroller. What I want to do I want to use the DMA to ...
5
votes
2answers
3k views

Why is the median filter called 'edge-preserving'?

I want to know about median filtering. Recently, I read that it is best for preserving edges. But how does it preserve edges? I need complete knowledge of median filters. Why it is non-linear filter ...
2
votes
1answer
166 views

Is Savitzky-Golay filter a special case of an FIR lowpass filter?

The Savitzky-Golay filter is explained here. It looks to me that any Savitzky-Golay filter can equally be considered an FIR filter. Am I right about that?
2
votes
0answers
55 views

What Techniques Are Used for Signal / Image Denoising (Example Image Provided)?

I have an image that looks like this (it might appear low res in a browser because it is 16 MB). This image was taken with a scanning electron microscope, but because the equipment is outdated there ...
3
votes
3answers
4k views

Low pass filter algorithm origin

I have been doing some research, because I used this algorithm that's very spread in the web: y += a * (x - y) or ...
1
vote
0answers
283 views

Converting floating point IIR to fixed point arithmetic, given its difference equation

Is there some general way to perform the task given in the question? I have a filter given as follows: ...
-1
votes
1answer
459 views

Forward Backward filter Scipy - $\tt signal.filtfilt$ changes the amplitude when $\tt signal.butter$ is used with $\tt btype='high'$

In the plot below the blue wave is the original signal. The orange wave is after the low pass filter. The green wave is after the high pass filter. I have a noisy ECG signal stored in the ...
2
votes
2answers
259 views

Magnetometer coil equalization

I have a search coil magnetometer with two coils, one at each end of a ferromagnetic core of high magnetic permeability: Figure 1. Double search coil magnetometer. (Modified from a drawing CC BY-SA 3....
1
vote
2answers
305 views

Determine filter type (HPF or LPF) by its coefficients

I want to determine optimal initial states for a FIR/IIR filter to get rid of oscillations and shifts at the initial interval. I've found that these initial states depend on filter type in the ...
3
votes
1answer
102 views

Can the overlap-add method be used with varying cut-off frequency filter?

I'm writing a software analogue synth. I have been using the Overlap-add method to cheaply implement a low-pass filter using FFT. My low-pass filter has had a constant impulse response; a constant ...
0
votes
3answers
636 views

How to Design Nonlinear Phase FIR Filter?

I've recently encountered a rather clever low-pass filter that appears to have been designed to sacrifice uniform group delay in the pass-band to get better frequency response relative to the filter ...
1
vote
0answers
177 views

How use FIR filter for simulating an integral implemented using the trapezoidal integration?

Suppose I have this equation $$ \phi = \frac{60}{T^5} \int_0^T \left( T^2 - 6T \tau + 6\tau^2\right) y(t-\tau) d\tau - \frac{30 \alpha}{T^5} \int(T-\tau)^2\tau^2 u(t-\tau) d\tau $$ and I want to use ...
0
votes
1answer
354 views

how to understand frequncy response and lowpass filter?

I am troubled with understanding freqency response. In lecture, my teacher talked about $H(f)$, which i know means that the response depend on frequency, $f$. But when I read text book, it uses a ...
0
votes
1answer
227 views

FIR filter design with flat passband but equi-ripple stop-band

I am looking for a lowpass FIR filter with flat passband but equi-ripple stopband. In other words, it likes Chebyshev_filter Type II except that it is FIR instead of IIR. Linear-phase is preferred. ...
1
vote
1answer
216 views

FIR Filters - Type 3

So I understand that a type 3 filter is not suitable for a highpass filter design, but is there any reason why it isnt suitable for a lowpass filter? So ultimately, can a type 3 linear-phase FIR ...
6
votes
2answers
3k 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:} ...
1
vote
1answer
693 views

Filtering an acceleration signal

I have a triaxial accelerometer giving me acceleration along x, y, and z. I then combine the 3 axes by calculating magnitude of acceleration over all time points (details in my question here) I'm ...
3
votes
1answer
236 views

Fractional Delay Filters and Cutoff Frequences

I am trying to implement an interpolator for arbitrary sampling rate conversion of a one-dimensional signal (a fractional delay filter). I am aware of the fact that interpolation is in general a ...
1
vote
1answer
5k views

Differences between low-pass, band-pass, notch filters

I'm studying image processing and I know that there are different filters you can apply. I don't understand the difference between the low-pass/bandpass/notch filter (or high-pass/band-reject/notch). ...
4
votes
1answer
4k views

Simple software low pass filter

I am measuring voltages and currents of a 3-phase electrical machine and I need to calculate the power. Every interrupt (frequency between 30-70kHz) I get values (voltages, currents) from analogue-...
-1
votes
1answer
142 views

Cepstrum analysis - Cut off frequencies displayed

My inquiry is regarding the so called cepstrum analysis. By conducting some experiments, i have real time data at my disposal. The acquisition rate is 1600Hz. I wanted to try cepstrum analysis just ...
0
votes
1answer
233 views

Is ideal LPF a LTI system? And is it time invariant?

Ideal filter time-domain impulse response is $$h(t) = 2B \operatorname{sinc}(2Bt)$$ It is not causal nor BIBO stable. Is it time invariant? And how can i prove it?
1
vote
0answers
13 views

is there upper limit on averaging window size for images?

An amateur question. I take an image and average pixels over a window 3 by 3, thus obtaining a smoother image. Then I increase the averaging window size - obtain an image with even less details, but ...
3
votes
2answers
4k views

Low pass vs band pass filter

I've been reading some EEG papers where the authors use a bandpass filter at, say, 1Hz and 30Hz. I've also seen some accelerometer papers where they bandpass at 0.5Hz and 10Hz What is the difference ...
0
votes
0answers
197 views

Slope of the Filter [duplicate]

I have this problem where I have to design a low pass filter with a slope of -6dB/octave. Now I don't know what this means and How to get it done? I would be glad if anybody could help me out ...
1
vote
1answer
305 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 ...
3
votes
1answer
226 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 ?
0
votes
4answers
127 views

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-...
1
vote
4answers
2k views

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 ...
4
votes
1answer
449 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 $$\...
-1
votes
1answer
389 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 ...
1
vote
2answers
2k 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 ...
0
votes
3answers
155 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 ...
0
votes
1answer
334 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 ...
1
vote
1answer
479 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)...
0
votes
1answer
93 views

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(...
3
votes
2answers
1k views

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: ...
5
votes
1answer
929 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 ...
0
votes
1answer
65 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 ...
1
vote
0answers
161 views

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 ...
0
votes
1answer
363 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 = $4$) ...
1
vote
0answers
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 ...
0
votes
1answer
256 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 ...
-1
votes
1answer
231 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, ...
0
votes
1answer
361 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 ...
2
votes
2answers
412 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 ...