Skip to main content
OverflowAI is here! AI power for your Stack Overflow for Teams knowledge community. Learn more
9 votes
Accepted

What is zero-phase filtering and forward-backward filtering?

Zero-phase filtering is a non-causal procedure, so it cannot be done in real time, only offline for IIR filters or pseudo real-time, i.e., with a sufficient delay for FIR filters. A zero-phase filter ...
Matt L.'s user avatar
  • 90.3k
8 votes
Accepted

Does Higher Sampling Rate Increase SNR?

Sampling at a higher rate will distribute the quantization noise over a wider frequency, thus reducing the noise spectral density due to quantization noise specifically, with a lot of caveats. For ...
Dan Boschen's user avatar
  • 51.9k
7 votes

Amplifier Placement in a Wireless Receiver

Placing the amplifier first will result in a lower noise figure for the receiver and hence more sensitivity but the amplifier will be exposed to all of the ingested signals, including undesired ...
GrapefruitIsAwesome's user avatar
6 votes

Simple software low pass filter

A first order lowpass filter is usually implemented like this: $$p[n] = \alpha p[n-1] + (1-\alpha) pi[n]$$ Where $p[n]$ is your filtered power estimation, $p[n-1]$ is the previous result, $pi[n]$ is ...
Juancho's user avatar
  • 5,026
5 votes
Accepted

Interpolating/Decimating CIC Filter Group Delay

Consider an $D$-tap FIR filter with liner phase, the group delay (measured in samples) is $$g=\frac{D-1}{2}\tag{1}$$ and therefore, if it is measured in seconds it will be $$g=T_s\frac{D-1}{2}\tag{2}$$...
msm's user avatar
  • 4,285
5 votes
Accepted

preprocessing raw ECG data

I need to preprocess raw ecg data in R, here is a sample already standardized. I'm not an expert in signal processing nor experienced in working with medical data,... Not being an expert on how the ...
A_A's user avatar
  • 10.7k
5 votes

Adaptive filtering: Optimum filter length and delay

In order to be able to choose an optimal value for the delay $\Delta$ it's important to understand how the system works. The purpose of the delay is to decorrelate the desired signal $s(n)$ and the ...
Matt L.'s user avatar
  • 90.3k
5 votes

Filtering without using any transforms

You can achieve this result by using two combs filters : https://en.wikipedia.org/wiki/Comb_filter Put simply, the comb filter consists of adding a delayed version of the signal to itself, causing ...
Albits's user avatar
  • 316
5 votes
Accepted

Filter before or after multiplication of two signals?

A personal rule: in general, it can be better to perform non-linear operations before linear ones. One reason behind that is that a lot of practical concerns are related to outliers or suspect ...
Laurent Duval's user avatar
5 votes
Accepted

How determine the delay in my signal practically

The Least Mean Square solution to find the "channel" or response of the filter is provided by the following MATLAB/Octave Code using the input to the filter as tx and the output of the filter as rx. ...
Dan Boschen's user avatar
  • 51.9k
5 votes
Accepted

Derivation of the lowpass to bandpass transformation

You're right that the multiplication of a low pass and a high pass filter results in a band pass filter, as long as the cut-off frequency of the low pass is higher than the cut-off frequency of the ...
Matt L.'s user avatar
  • 90.3k
5 votes

How to estimate the local trend in a signal?

Start simple: just use a 1-D median filter of an appropriate length. If I do that with a length of 100 samples, I get the following for your first signal. The top plot shows the original signal (blue)...
Peter K.'s user avatar
  • 25.8k
4 votes
Accepted

Smoothing a staircase

Looks like your data is virtually free of noise. That, combined with a very high sampling frequency would mean that at the jumps the data is exactly at the threshold between two quantized values. Set ...
Olli Niemitalo's user avatar
4 votes
Accepted

Undoing a filter operation in MATLAB

In general it's only possible to implement causal and stable filters. There are exceptions where marginally stable filters are used, but this doesn't apply here. So if you want to invert a given ...
Matt L.'s user avatar
  • 90.3k
4 votes

Do integration/differentiation processes work as simple filters?

Yes, integration and differentiation can be linear filters. You can start from laplace properties that say: $ \int_{0}^{t} {x(t)dt} \longrightarrow \frac{X(s)}{s} \...
4 votes
Accepted

What are the advantages and disadvantages separability of Gaussian 2D filter?

Assuming the simplest case with a square image $x[n,m]$ of size $N \times N$ and a square filter kernel $h[n,m]$ of size $M \times M$, the raw 2D convolution to produce the, cropped, output image $y[n,...
Fat32's user avatar
  • 28.3k
4 votes

Filter before or after multiplication of two signals?

In general you will need to multiply first and then low pass filter. You also have to make sure that your sample rate is high enough so the multiply doesn't create aliasing. Let's look at a simple ...
Hilmar's user avatar
  • 45.3k
4 votes
Accepted

Filter: IIR Filter

There are many ways to arrive at filter coefficients, depending on your specs. But from your question I assume that you're talking about basic second-order building blocks (biquads). Also here there ...
Matt L.'s user avatar
  • 90.3k
4 votes
Accepted

A Simple Algorithm to Filter / Smooth / Denoise a Noisy Staircase Graph

Assuming you meant to produce something similar to the green line: What about $$\text{output}[n] = \max\{\text{input}[n-k], \text{input}[n-k+1], \ldots ,\text{input}[n]\}$$ i.e. you just find the ...
Marcus Müller's user avatar
4 votes
Accepted

Using oversampling to increase resolution of a DC-signal as input

My input signal is a dc signal (sensor output) and im getting kind of a headache to understand why oversampling can increase the resolution of dc signals. The ADC puts out integers. So, let $x$ be ...
TimWescott's user avatar
  • 12.8k
4 votes
Accepted

How to implement the recursive FIR filtering of a signal with zero boundary condition?

New Answer I think there is a much easier and more general way to tackle this. Let's assume we have a sequence of $h[n]$ that has finite support on $[K,L]$ where $K$ is the index of the first non-zero ...
Hilmar's user avatar
  • 45.3k
4 votes
Accepted

Amplifier Placement in a Wireless Receiver

GrapefruitIsAwesome's answer is right in mentioning that Friis noise formula says to put the most amplification possible as far up front as possible to minimize overall noise figure, but I'd like to ...
Marcus Müller's user avatar
4 votes
Accepted

Autocorrelation function of a filtered periodic signal

(Note to others: Please don’t edit this yet as OP and I are still working through certain details to make this clearer… once this not is gone, feel free to make updates ) This was a (advanced) ...
Dan Boschen's user avatar
  • 51.9k
4 votes

Why does convolution give the output of a passing a signal through a filter?

You can describe the system with an operator acting over an input $x(t)$ transforming it into $z(t)$. If $L$ is the operator, $z(t)=L[x(t)]$. Remember that the system and the operator are linear and ...
Andy R's user avatar
  • 91
4 votes
Accepted

What's the point of differential beamforming?

Introduction To my (rather limited) knowledge, the main advantage that made Differential Microphone Arrays (DMA) popular is their ability to have a frequency invariant beampattern (up to some certain ...
ZaellixA's user avatar
  • 1,314
4 votes
Accepted

Understanding the Farrow Filter

I like this diagram a little better (it's equivalent) Now, while most of the time the Farrow structure is associated with Lagrange interpolation, it need not be Lagrange. It can be any decent ...
robert bristow-johnson's user avatar
3 votes

Optimal Level of Wavelet Decomposition for Denoising

Best denoising should be related to certain quality measures, often requiring the clean signal reference, which you do not have in general. Or you could rely on some reference-free measures. To the ...
Laurent Duval's user avatar
3 votes

preprocessing raw ECG data

I do not have a lot of experience in analysing ECG data. However, it does not look, to me, like any ECG I have seen, or the patient is stone dead. I would at least expect a "regular" baseline, and ...
Laurent Duval's user avatar
3 votes

Does a filter add oscillations to a signal?

A linear, time-invariant system such as a filter is incapable of producing frequencies that are not already present at its input. One simple way to see this is that if the system's frequency response ...
MBaz's user avatar
  • 15.3k
3 votes

Does a filter add oscillations to a signal?

A linear filter can increase the magnitude of frequency spectra already present in a signal. Note that the Fourier Transform of any (reasonable) waveform or signal (including ones that do not look at ...
hotpaw2's user avatar
  • 35.4k

Only top scored, non community-wiki answers of a minimum length are eligible