# 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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### Apply Low pass Butterworth filter in Python

I want to use a low pass Butterworth filter on my data but on applying the filter I don't get the intended signal. Here is the dummy code: Signal A: ...
351 views

### Short length windowed sinc filter

I have a 50-60Hz signal being sampled at a frequency of 25 kHz & I'm trying to filter all frequencies beyond 70 Hz with a reasonable steep transition band (approx 4 Hz) & good attenuation (~40+...
76 views

### Help generating coefficients for basic FIR LPF

I'm trying to generate coefficients for a FIR low pass filter to be used in an FPGA. I'm using python (scipy.signal) to attempt to do this, but am having trouble getting coefficients in a usable form....
41 views

### What does “ripple limit cutoff” mean?

So I'm reading the datasheet for MAX98357A. It's an audio amplifier that receives digital signal using I²S bus and has integrated digital low-pass filters of the IIR and FIR types. In addition to ...
310 views

### How to properly filter a BPSK demodulated signal?

I am new to this field and yesterday I began a project for BPSK modulation. So this is what i did: $\ x(t) = 0$ or$\ 1$ binary data $\ Fs = 15$ sampling frequency kHz $\ Fc = 10$ carrier ...
440 views

### Condition for modelling noise as white noise

I am reading a book on Communication System by Simon Haykin. In the topic of white noise there is a paragraph "We may state that as long as the bandwidth of noise process at input of a system is ...
361 views

### should I apply low-pass filter when calculating central derivative?

Let us say that we have a discrete signal $I_n$, $n=0, 1, 2, ...$. According to Nyquist theorem the maximum frequency for such discretization is $f_{max} = 0.5$. Now imagine that I want to calculate ...
307 views

### AM demodulation from a real RF signal

I'm capturing an RF signal transmitted at 433.8MHz, with a bandwidth of about 50KHz. My goal is to be able to save it as a .wav file. I'm using an RTL-SDR dongle and a software named HDSDR, where I ...
206 views

### How to smoothen signal with missing values before differentiation?

I want to differentiate a noisy signal with many, randomly located, missing data values. Which smoothing techniques should be applied before differentiating the signal? I have a velocity signal at ...
144 views

### Instantaneous velocity and displacement from acceleration signal using a proper filtering method

first I need to mention I'm new to signal processing. here is the situation: I have an acceleration time-series derived from an accelerometer I wanted to imply a filtering method like high pass ...
4k views

### AM Modulator Demodulator in Python

I am trying to make a AM modem using Python Numpy and Matplotlib. I am successful in generating the AM Signal but I cannot demodulate it using a lowpass filter function that I made. The demodulation ...
105 views

### How to filter a signal sampled at different frequencies

I have a signal which was sampled using different frequencies. The 3 regions are: 0-10 ms: 10000 Hz 10-50 ms: 1000 Hz 50-200 ms: 100 Hz The signal is very noisy, so I thought about smoothing it with ...
2k views

### Implement a Butterworth Filter in C#

I'm very new to signal processing, but was asked to implement a filter function for Butterworth low pass filter for given order, cutoff frequency and sample rate. After reading some articles I think ...
349 views

### how can I make a simple lowpass filter with this constraints? [closed]

I'm searching for a simple low pass filter code in C with this constraints a modulable frequency cutoff (how can I convert all these crazy coefficients into a frequency?) I could change with a slider....
7k views

### Apply butterworth filter (lowpass) to a signal

I'm working on a DSP lab and I can't figure out how to apply the filter I've created to a sound. The only thing I found online that did something to my sound was ...
103 views

### Can I combine an IIR (an EWMA) with a maximum?

I'd like to have a exponentially weighted moving average (EWMA) which is raised to the value of the input signal whenever this is higher than the filter output. This taking of the maximum shall take ...
85 views

### Can I use IIR or FIR to get a sliding mean?

My output signal shall be computed by (meta code): o = 0 # or some arbitrary initial value for i in input: o = (o * 99 + i) / 100 print o I call this a "...
366 views

### Design Lowpass Filter With -7.5 dB/Octave Rolloff

I am working on a project that needs a lowpass filter with a -7.5 dB/Octave rolloff. This is somewhere between the rolloff of a one-pole and two-pole filter, so I wanted to ask what some standard ...
154 views

### Compensate for FIR filter attenuation

Is there a simple way to compensate for the reduction in amplitude of a low pass filter of a noisy sine wave signal that has been smoothed using a FIR filter so that the amplitude of the smoothed sine ...
572 views

### “fred harris rule of thumb”:

I would like to cite "fred harris rule of thumb" for estimating filter order. Is there a book or paper where I can find this rule of thumb? Thanks a bunch.
623 views

### What is the name of this digital low pass filter?

I found this digital filter in code I am working on. It is a low pass filter. In the code it is called an "alpha filter", but it is not the same as the alpha filter mentioned here. I post the ...
833 views

### 2D Fourier transform of Sobel kernel

Can someone explain me the highlighted text parts regarding this image ? Here is a pseudo-code of how it was created: ...
2k views

### Gaussian filter as a low pass filter

Can anyone explain me how is a Gaussian filter a low pass filter? It may be a simple thing but I just can't seem to wrap my head around it. Also while applying a low pass filter for bandlimiting (to ...
118 views

### Determine filter given transfer function [closed]

I am given $$H(z) = 1 + \frac{\alpha}{1-\alpha z^{-1}}$$ where alpha is between $0$ and $1$. This is apparently is a low-pass filter with cutoff frequency $f_c$. How can I see that? And how can I ...
505 views

### Consider an ideal low pass filter $H(\omega)$, and the input to this filter is the periodic square wave $x(t)$. Find the output $y(t)$

The solution to the problem is $$y(t) = 5 + \frac{20}{\pi} \sin(\pi t) + \frac{20}{3\pi} \sin(3 \pi t)$$ and to get that the solution says to find the Fourier series expansion of $x(t)$ and I am ...
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### Digital Lowpass Filters, basic questions

Forgive the newbie questions, I'm just starting out and wanted some basic information. I have a signal coming from a digital gyro, most of the useful information is below 90hz but I am seeing ...
47 views

### Low pass image filter

I have feature in my camera that indicates "Low Frequency Flat Field correction" and I want to evaluate its impact on the image. How can I do this? Currently I can only take pictures of a uniform ...
273 views

### Applying Jake's remez exchange algorithm for filter design

I have found C implementation for remez exchange algorithm(https://github.com/janovetz/remez-exchange/blob/master/remez.c) and I want to use this to implement a generic prototype lowpass filter. ...
1k views

### Upsampling before performing pulse shaping

I know what an upsampler does. We insert L-1 zeros between the samples. As a result, it creates spectral repetitions. What if we have a symbol impulse stream and then we apply a Root Raised Cosine ...
34 views

### Overview of regression methods between the data

I am trying to find different approaches (classic and modern) in order to find a regression function between data (in time domain) with high-frequency noise. Consider the result of this code (in ...
135 views

### Apply LTI filter to incoming signal stream [duplicate]

Typically, when I want to filter a signal with an LTI filter (in this case a low-pass filter), I just convolve the signal with the filter. However, what do I do if I have a stream of data that I want ...
1k views

### Lowpass Lanczos filter

I am new to Lanczos filters and trying to figure out how they can be used to generate a zero-phase lowpass filter with good time-domain properties. This example shows how to implement such a filter in ...
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### Design of a Butterworth lowpass filter in MATLAB

I'm using the Signal Processing Toolbox in MATLAB to design a Butterworth low-pass filter. I'm told that my filter has been giving some unexpected results. In particular, when the values from this ...
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### Removing low frequencies from a signal

I am trying to remove low frequencies from a signal and intuitively I chose the high-pass filter, more specifically - a Butterworth filter, Order 4 (because I am not sure how to choose properly the ...
111 views

### What is the reason for this 'linear “error”'

Here's MIM (Magnitude Invariance Method) thesis (press the "View PDF" to get the theis with MATLAB code in hands) and here's a plot showing the issue I'm trying to solve: Magnitude responses for one ...
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 ...
2k 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 ...
10k 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}}...
536 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 ...
97 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 ...
4k 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 ...
194 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?
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### 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 ...
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### 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 ...
356 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: ...
548 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 ...
278 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....
327 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 ...