# 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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Single ADC is sampling at 16000 Hz the I and Q outputs of quadrature detector. So each I and Q signal is sampled at 8000 Hz, with phase offset 90 degrees between them. Bandwidth of interest is 3400 Hz....
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### Research on SDR security Gnu Radio and legal transmission with filters

In fact, I am doing research around SDR and possible dangers. Then I stumbled upon the most well known "replay attack". Via Black hills, I came across the following diagram in gnuradio: The ...
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### Cascading IIR filter with All pass filter (APF) for constant group delay and linear phase over the passband using MATLAB not working?

I've designed an IIR Low pass filter in MATLAB with the following parameters. ...
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### Low pass filter behavior in frequency domain

I have a relatively simple task, which is to implement a low pass filter for a sum of exponentially dampen complex sinusoids in random Gaussian noise. To showcase my problem I have generated data ...
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### Does LPF limit the maximum sampling frequency of the input signal? [closed]

Consider the system where the signal passes through analog LPF with cutoff frequency of 50 Hz, so the maximum sampling frequency of the input signal could be 100 Hz (according to the theorem). But can ...
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### Windowed Sinc vs Parks–McClellan filter design [duplicate]

In the context of FIR filters, what are the tradeoffs between using a low pass filter designed using a windowed sinc versus an optimally iterative algorithm such as Parks-McClellan? When would you use ...
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### What's the interpretation of this Low pass filter spec?

From the filter characteristic mentioned in the table, is it correct to interpret following for LPF: Fs=192Khz Passband edge=43.8Khz; passband ripple=5mdB Stopband edge=112Khz; stopband attenuation=...
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### Designing of passband and stopband frequencies

good evening guys, let us consider following image we can see from the picture designing of lowpass filter with given passband region and stopband region, only one thing what i am interesting is ...
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### Simulation of Lock-In Amplification in Python makes no sense

I would like to simulate a basic lock-in amplification for post-processing some data. I wrote a basic Python script for this purpose but the output of the lock-in amplification does not seem to make ...
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### How to properly filter offline data by zeroing the unwanted frequencies after FFT?

I am new to the field of DSP. I have a measured signal, and I wanted to apply a low pass filter on the data. I just simply applied FFT, wrote zeroes at the unwanted frequencies then applied inverse ...
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### What formulas do I need to add poles to these two filter designs

I am coding a music composition application and it uses a couple of different types of filter effects. I have implemented single pole, two pole and sinc filters to it successfully. I would now like to ...
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### Lowpass Filter for Lock-In-Amplifier

I am implementing a Lock-In-Amplifier in Python with scipy for measurements with light with a decimation afterwards. Right now, this is implemented with an average. This works fine, but I am trying to ...
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### Why I don't have phenomena of aliasing after resize image in frequency domain?

I'm writing code in cuda/c++ languages to resize images. I used a box filter ( it response in spatial domain is sinc filter ) and I have applied the convolution theorem and I'm using the fourier ...
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### Does a FIR filter $H(z)$ with maximally flat passband group delay response satisfy $|H(e^{i\omega})| \leq 1$? [closed]

From this paper (Maximally flat low-pass FIR filters with reduced delay) and others, I know that it is possible to impose maximally flat passband group delay response constraints. Suppose that I do ...
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### Low-pass vs. windowing function in front of FFT

I am sampling sound at 48 kHz because that's what the DAC for the headset needs. I take every 6th of these. So I have 8 kHz and process 1024 at a time. My goal is to analyse the spectrum in the final ...
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### Impulse response of IIR low-pass filter

(Disclaimer. I have started doing some DSP. The last time I worked with this was in the eigthies. And I wasn't much of a specialist then, either.) Is the impulse response different for IIR and FIR ...
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### FFT denoising vs low pass filter

Say I have a noisy signal in which I want to denoise. There's two methods I'm considering FFT denoising, where I take the FFT of the signal and then threshold somewhere, attenuate all the frequencies ...
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### A real-time (causal, non-symmetric) lowpass FIR filter with minimal passband ripple and phase

I am looking for a lowpass FIR filter that is causal (all samples used are current or past) and exhibits very low passband ripple and has passband phase very close to zero, which necessitates a filter ...
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### Accounting for phase shift in time-dependent signals

Background: I am using a vibration sensor and arduino to record signals and log them with timestamps, where the signals need to be time accurate so that I can glean information about which frequencies ...
1 vote
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### Matlab: How to design digital equivalent for a lowpass Bessel filter (Thiran filter)?

In the process of applying a lowpass Bessel filter to my signal, I realized that besself function does not support the design of digital Bessel filters and the bilinear function can be used to convert ...
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### Need for rectification in cochlear implants

In cochlear implants, the input signal is fed to a set of bandpass filters and then half wave rectified and low pass filtered to estimate the envelope signal. What is the need for doing rectification? ...
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### Normalize Bessel filter

I am applying a low pass filter to my signal and I should make sure the transfer function of my filter is one. How can I normalize my filter? I am learning about filters and I appreciate any help. <...
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### second-order buttworth low pass filter in python code

i have difficulty in understand the function freq_response(),i have already knew that the coefficient is for 2-order butterworth LPF, i want to change it into 3-order,what does the "phi" and ...
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### filter noisy angle signal

I'm receiving a angle signal with values in the range [-180..180] Now I want to smooth that signal over time. I'm already using 1€ filter quite successfully on some of the other values I need to ...
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### Convolution between bit stream sampled by N number of samples per bit with a channel modeled as low pass filter

I generated a bit stream in MATLAB, from the transmitter to be convoluted by the channel I use MATLAB function "randi" between 0 & 1, so it generates random vectors of 0s & 1s and ...
1 vote
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### Convert matlab line to scipy signal processing line

I am converting some legacy matlab code to Python and I'm struggling to find the right function in python from the legacy code. The matlab filter is ...
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### I do not understand the frequency calculation used in the construction of this IIR digital Butterworth Low pass filter using MATLAB

The question is to design a Low Pass Butterworth IIR Digital filter. The following code below has the specifications with $A_p$ being the passband attenuation, $A_s$ the stop band attenuation, $f_{pb}$...
1 vote
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### How to know if filter is lowpass or highpass?

I was trying to solve the following question: Calculate the DFT of the given filter impulse response $h(n,m)$. Based on the result, determine if the given filter is a high-pass or a low-pass filter. ...
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### Ideal low pass filter with cut-off B does not affect a band-limited baseband signal with maximum frequency B

Let $x(t)$ be a band-limited signal with spectrum (fourier transform) lying between -B and +B. Such a signal is not warped by an ideal low-pass filter with cut-off frequency equal or higher than +B. ...
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### Basic question about Bandpass and lowpass filter using Python

I have a signal that is the sum of 3 signals that has just passed through a transmission channel. I need to put filters to this signal (bandpass and lowpass) and then apply demodulation and get one of ...
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### GNU Radio Low Pass Filter doesn't work as expected with different transition widths

I'm new to GNU Radio and signal processing. I don't know if the following is a simple question, but I have been scratching my head about it. I created a simple flow graph with a random source (0-3) ...
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### Choosing a good low pass filter in the wavelet scattering transform

What's the impact of a specific filter $\phi$ when building the wavelet scattering transform? I mean, if I compute the MFCC choosing different windows, (Hamming, Blackman, etc.), the behaviour ...
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### Pressure signal

I have got an raw file which has pressure and time and temperature format and after coding I have got the plots but my main task is to analyse the data and understanding the influence of Bessel and ...
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### Frequency response of an ideal low pass filter

I have an ideal low pass filter having unity gain and cutoff frequency 100Hz. If I provide an input having single frequency component at 100Hz(E.g.- cos(200pi t), will the low pass filter block the ...
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### Find the output signal in a Low Pass Filter for a given cutoff frequency range

I have a scenario where 𝑥(𝑡)=2⋅sin150𝜋t +sin250𝜋t and g(t)=𝑥(𝑡)sin250𝜋 . The signal g(t) is passed as input through an ideal lowpass filter with cutoff frequency(fc)= 300𝜋 and passband gain= 3....
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### Find the band pass signal for a given low pass range and cutoff frequency?

We know the fact that a bandpass signal is defined for real values. But for a typical scenario where we have a signal in the lowpass range:say : 𝑥𝐿(𝑡)=𝑗𝑋0 sinc(Bt) and the transformation of the ...
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### Signal filtering with physical limitations and estimated STD

I have a prediction mechanism that predicts some signal value. Generally the prediction look like this: The are some ranges of systematic error and I cannot do anything with this. But in many points ...
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### Why the received SNR increases with bandwidth?

I am performing the following simulation: Complex chirp signal with bandwidth [-B, B] is transmitted through a multipath channel which has $N$ taps all being complex Gaussian variables (i.e., ...
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### Requirements on Signal Spectrum for Fractionally Spaced Equalization

I'm constructing an ultrasonic communication system and I am struggling with the correct parameters for my receiver. In baseband, my channel input signal $x(t)$ has infinite bandwidth, since I use a ...
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### Difference equation from a transfer function of a low pass filter

I need to get the difference equation from this transfer function: $H(z) = g \frac{1+a_1}{1+a_1z^-1}$ My math skills are too many years old, but I remember I need to get the Y(output) on one side and ...
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### RT 60 from Impulse response

I have already the impulse response of an acoustic environment in the form of a series of signals over 300 samples. I have tried the procedure given in this platform - i.e. low pass filtering, Hilbert ...
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### Why is my low pass filter decreasing the amplitude when using the inverse DTFT?

Goal: I'm trying to model a waveform in the time-domain for pattern recognition. My plan: Convert signal to frequency domain using FFT Reduce harmonics to hopefully isolate residual data, and make it ...
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### What is the transfer function of the filtfilt?

I designed a Parks McClellan filter to design a lowpass filter. First, I created the order of the filter with firpmord(). Then I designed the filter with firpm() and created the impulse response. I ...
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1 vote
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### Why an does an integrate-and-dump stage in a CIC filter provide the same functionality as the integrator and comb in series?

I have a hard time understanding why the combination of integrator and comb (integrate-and-dump) is the same as a separate integrator and comb in series like in this picture: Please explain why these ...
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### My beat detection algorithm via a low pass filter is bad. Looking for tips for improvement with good trade-off between complexity and accuracy

In spring, I built a beat detection algorithm in Rust. It works for very simple songs but the problem is that I have to adjust the parameters of the algorithm manually for each genre and sometimes for ...
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### Do we use calculator in radians or degree while calculating prewarping analog frequency in Bilinear Transformation?

Say $\omega_s=1.96\;,\omega_p=0.785$ For bilinear transformation-: $\Omega_p=2/T*tan(\omega_p/2)$ $\Omega_s=2/T*tan(\omega_s/2)$ Should I put my calculator in radian mode or degree mode. I believe it ...
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### Do we guess the cut off frequency when passband edge frequency and stop band edge frequency are given? FIR Filter design-LOW PASS FILTER

Say passband edge frequency=0.25 $\pi$ Stopband edge frequency=0.35 $\pi$ What is the cut off frequency? Do we average these 2 frequencies and write the answer or what is the procedure to find cut off ...
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### How to identify low pass, bandpass, band reject, high pass filter etc from given $|H(e^{j\omega})|$?

1) How is this a low pass filter? $0.99 \leq |H(e^{j\omega})|\leq1.01 {\rm\ for\ } 0\leq|\omega|\leq0.19\pi$ $|H(e^{j\omega}\;)|\leq0.01{\rm\ for\ } 0.21\pi\leq|\omega|\leq\pi$ 2) What kind of filter ...
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### Butterworth Filter Transfer Function

Butterworth Filter frequency response is given as: $$H_a(j\Omega)=\frac{1}{\sqrt{{1+\left(\frac{\Omega}{\Omega_c}\right)^{2N}}}}\quad \text{where N is the order of the filter}$$ and for the transfer ...
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Design the FIR filter using suitable window for the specifications-: $0.899\leq |H (e^{j\omega}\;)|\leq1\;for\; |\omega| \leq0.2\pi$ \$\; |H(e^{j\omega}\;)| \leq 0.01, \text{ for } \; 0.4\pi\leq \...