Questions tagged [filters]

In signal processing, a filter is a device or process that transforms a signal by selectively choosing specific frequencies and leaving others with appropriate gain or as it is.

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36 views

Transform lowpass filter to highpass filter, what happened to unit sample response and difference equation?

I know that multiple a lowpass filter signal by $(-1)^n$ can transform it to a highpass filter. $$ s_{hp}[n]=(-1)^n s_{lp}[n] $$ But exactly what happened to the unit sample response and difference ...
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Phase in FIR filters [closed]

Does anyone have any idea what is Clear Phase technology ? How is it implemented ? And which audio channels whether left ,right center , sub woofer should have this technology implemented and why ?
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Confusions in windows based design of FIR filters?

I am reading the proakis book"DSP USING MATLAB 3rd Edition" In chap 7, article 7.3, i came across example 7.8,where i saw formulas for pass band ripple and stop band attenuation I have ...
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Help identifying filter

Apologies in advance for asking something so basic, this is not my field at all so I'm a bit lost where else to find this info. I'm trying to understand this piece of code that detects sudden drops in ...
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1answer
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Frequency domain filtering: must filter coefficients always be conjugate symetric?

While trying to do frequency domain filtering of audio signals using windowed overlap-add methodology, I came across some pre-calculated frequency domain coefficients. I noticed that the coefficients, ...
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24 views

Calculate moving RMS with exponential averaging

This is moving RMS, now how to add exponential averaging in this df['signal'].rolling(21*24*60).apply(lambda x: np.sqrt(x.mean()))
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94 views

On what it means for a system to be minimum phase

From my undestanding I get that when a system's poles and zeros are all inside the unit circle then it means that it's minimum phase. But I don't get how the location of zeros and poles are related to ...
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What is phase shift?

I'm reading about when a $H(z)$ system is min phase or max phase, and I get when a system is a min phase or max phase depending on the location of the zeroes. But I don't get at all the phase shift ...
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1answer
54 views

Calculation of inverse impulse response in the frequency domain

I want to calculate the inverse impulse response of a LTI system in the frequency domain. I generate a simple impulse response $g$. For this I generate a vector of 100 zeros. I set the value of the ...
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Finding the wiggles pattern in the original dataset. (Wiggles appear after performing division by another dataset)

I have multiple measurements regarding scientific observations. The problem is that there is a subtle noise pattern caused by the instrument - the wiggles. These wiggles are invisible when looking at ...
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3answers
920 views

Comb filter - attenuation

I have a signal and from 'standard information' I know the predominant frequency is at $1\textrm{ Hz}$ and then there should be three harmonics at lower amplitudes. My signal however has a lower ...
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Speed measurement calibration

I have a sailing yacht where speed is measured using a peddle wheel. It measures speed through water (STW). This measurement contains a measurement error whose magnetude is dependend on both speed (it ...
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1answer
38 views

Signal Spectrum Shaping

I am looking for methods/algorithms for signal spectrum shaping. Let's say we have a white Gaussian noise and want to have a desired power-spectral density. The first solution that comes to mind is ...
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1answer
54 views

How can I find the transform function, amplitude and frequency response of a digital filter in python?

I have applied a laplace filter mask to an image and now I want to find the amplitude and freqency response of a laplacian filter: [[1,1,1], [1,-8,1], [1,1,1] ]. I know I need to first find the ...
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1answer
57 views

Edge detection in spatial or in frequency domain?

I want to ask why everywhere is used to do edge detection in spatial domain and not in frequency domain with FFT of image and apply HP filter. Thank you.
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1answer
109 views

How to achieve a smoothed frequency phase response with no outliers

I have two sampled signals, which I then perform wavelet analysis on, by synthesising the Filterbank, perform the dft on each kernel, and the dft on the sampled signals, and multiply together. ...
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What are the kernels that are used in the Smooted Psuedo Wigner-Ville distribution?

Defined in Matlab's docs for WVD, SPWVD is given by: $\int_{-\infty}^\infty g(t) * H(f) x(t + \frac{\tau}{2}) x^*(t - \frac{\tau}{2}) e^{-j2\pi\tau\,f} \, d\tau$ H(f) and g(t) are the smoothing ...
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1answer
144 views

Detect Gradual Increase Before a Decrease in Noisy Data

I have data that'ss not too noisy and I am trying to detect a pattern where it gradually increases then decreases in a short period of time (20 ticks? it should be roughly similar per session but can ...
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1answer
87 views

QPSK demodulation

My objective is to demodulate QPSK signal. At this moment, my constellation in the best case looks like in the picture below: and the corresponding eye-pattern: Eyes are completely closed, which ...
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2answers
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Why do FIR systems need to be antisymmetric about M/2 to be linear phase?

Why do FIR systems need to be antisymmetric about M/2 to be linear phase? where M=delay.Also im talking about discrete time.And why are hilbert transformers antisymmetric on n=τ?
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How to graph magnitude plots for basic 4-pole filters?

I have developed magnitude plots for basic one-pole and two-pole filters derived from various Physics PDF's and tutorials I have found online and calculated from: https://www.desmos.com/calculator/...
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2answers
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Relationship between order of filter and amplitude/phase response

I am learning about digital filters, for example a lowpass butterworth filter. In many languages, the implmentation requires specification of the order of the filter, which I believe is the number ...
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1answer
26 views

Bio-signal discontinuity after FIR filtering

I'm filtering respiration signal. I have a signal of duration equal to 10 minutes, so I decided to divided it into period of 10 s. I filtered each epoch with FIR filter, but I have discontinuities ...
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Accelerometer Bias estimation with kalman filter

I have to estimate biases of a 3-axes accelerometer by modyfying an existent kalman filter mounted on a drone. The biases are assumed constant. The filter has 9 states: position (xyz), velocity (xyz) ...
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Output of LTI (in time and frequency $\omega$ domain) : when input goes through LPF

I would like to raise a mathematical question : Let's say we are been given : $$x(t) = \begin{cases} \cos(\pi t) & |t| \leq 0.5 \\ 0 & \textrm{otherwise} ...
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How can I filter a noise with pattern type in audio?

I have a set of audio files rescued from a source of phonograph record like a gramophone. Very old family stuff records from my elders back in year 1946. A relative has digitalized these with a ...
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28 views

What happens to the audio of a reconstructed signal if we remove too much frequency?

Assuming we have an audio with noise embedded in it, I was wondering what happens theoretically if we remove (filter out) too much frequency when we pass LPF with a cutoff frequency lower than the ...
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192 views

Measuring group delay through a linear phase filter

I'm having a difficult time wrapping my head around a phase/ group delay problem and it corresponding to where you start sampling so I built up a system to test some of these issues. The system passes ...
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2answers
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Analysis of the ratio of two moving average filters

I have created a basic segmentation algorithm for 1-D signals (e.g. audio) based on a ratio of energy averages. The classification rule involves comparing the signal energy measured over a short time ...
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152 views

Where do RBJ's analog shelving filters come from?

In RBJ's Audio EQ Cookbook, the analog prototype for a low shelf filter is given as such: $$H(s)=A\cdot\frac{s^2+\left(\frac{\sqrt{A}}{Q}\right)\cdot s + A}{A\cdot s^2 + \left(\frac{\sqrt{A}}{Q}\right)...
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1answer
530 views

Discrete Wavelet Transform (DWT) Filter Bank

I have some stumbling block in my thesis writing. Do we use the same filter pair while implementing DWT filter bank with downsampling of the filter output, or filters do change also from level to ...
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1answer
124 views

Is the Bilateral Filter a Solution of Some Variational Method?

I've been watching these video lectures about variational methods in computer vision. In one of such video lectures a it is explained for example that the Gaussian filtering is a solution of the ...
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FIR Filter design, using different filter length than signal length

Given some neurophysiological application I am filtering in real time data of limited length (e.g. in epochs of 100 ms) using a sampling rate of e.g. 100 Hz. Due to this short time segment I am trying ...
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1st and 2nd Gaussian derivatives for edge detection

I have a project about edge detection, I made research on internet about filters and read many articles but there is an article talked about using Sobel and Gaussian derivatives then it mentioned &...
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1answer
55 views

Output power of a signal passing through an IIR filter

suppose I have the following discrete time signal $x\left(n\right)=0.7\sin\left(2\pi \times 623\:nT\right)$ where $N=4000$ and $T=\frac{1}{f_s}$, where $f_s=40$ kHz I pass this signal through a simple ...
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1answer
170 views

RC high pass filter differential equation

I have the question to derive: $$RC \frac{dy(t)}{dt} + y(t) = RC \frac{dx(t)}{dt}$$ which describes a high pass filter or $CR$ circuit with $x(t)$ the input and $y(t)$ the output. I am really ...
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1answer
33 views

Error introduced by smoothing filter at the end of a processing block

I'm running analysis on a multichannel audio signal and due to the size have decided to process it in blocks (my computer doesn't have enough memory to process it in one go). Some of the data produced ...
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2answers
81 views

My 3x3 Weighted Median Filter doesn't seem to be improving my image quality

In order to reduce noise in my training dataset,I attempted a WMF whose weights are shown in a 2-D array as follows(values finally get normalized by division by 15: ...
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1answer
108 views

Introductory resources to mathematical properties of “dynamically recalculable” filters in audio/musical equalizers?

Introductory resources to mathematical properties of "dynamically recalculable" filters in audio/musical equalizers? Particularly, I want to understand What mathematical features (e.g. monotonicity ...
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1answer
37 views

What is “filter periodization”?

A library defines periodize_filter_fourier, which is an equi-spaced averaging formulated by $$ v_f[k] = \sum_{i=0}^{\text{n_periods}-1} h_f[i\cdot N + k], $$ where $v_f$ is periodization of $h_f$, $N=\...
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2answers
229 views

How do I convert this simple Laplace equation to Z-domain?

A basic model of coupled strings (eg. piano) is provided here as: The principle is that it has two identical string simulations each formed by a delay line and LPF. The outputs of these are summed at ...
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1answer
317 views

How can a RLS algorithm utilise Wiener filter as FIR (M-tap) block?

I'm currently working with a dataset of $5000$ pulses of $N=15000$ samples each. I managed to implement the RLS algorithms with a FIR M-Tap filter such that $M\leq 15000$ ($150$ seems to achieve the ...
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1answer
132 views

reconstructing time-stretched signals for filtering purposes

I would like to know if it's possible to reconstruct the original time domain signal from it's time-stretched version? Is there any algorithm out there that can do this? Python, Matlab, etc? I want ...
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1answer
3k views

Why do we put poles close to the zeros in notch filter?

In the book I'm studying from "Applied digital signal processing - Manolakis" it says: The problem with FIR notch filters is that the bandwidth of the notches is large. A simple way to create ...
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1answer
81 views

Envelop detection using matlab hilbert function

I am trying to detect the envelope of a high-frequency signal (similar to below) using Matlab Hilbert function This is my output It generally follows the envelope, but there is a high-frequency ...
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2answers
36 views

Simple Image Edge Preserving Filter

I am after a simple, yet effective, Image Edge Preserving Filter. I need something which is faster than the Bilateral Filter with similar quality (The Guided Filter isn't good enough). Are there such ...
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3answers
105 views

Impulse response of an infinite-length system

I have a system which is expressed as following: $$y[n] = x[n] - \alpha y[n-N]$$ where $y[n]$ is the output and $x[n]$ is the input. When I take the z-transform of both sides, I've found the transfer ...
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1answer
34 views

Intuition behind lattice filters

In papers and textbooks and on Wikipedia, I regularly stumble upon so-called "lattice filters". They always look horribly more complex than their 'non-lattice counterpart' and I usually don'...
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1answer
358 views

Kalman Filter EM Estimation of Covariances

The question might be very simple, but I get a strange result from Kalman Filter. Let us consider the simplest state-space model, the random walk plus noise: $$ y_{t} = x_{t} + \varepsilon_{t}\\ x_{t} ...
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1answer
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Wave Digital Filter Bridge-T Resonator implementation, gives expected cutoff frequency but incorrect gain and roll-off

Trying to implement the WDF in Fig 5(a) of this publication. The response of the ideal op-amp implementation is given by the black curve in Fig 7: Here is the plot I get when trying to implement the ...

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