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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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Efficient implementation of 2-d circularly symmetric low-pass filter

How can a two-dimensional ideal circularly symmetric low-pass filter or its approximation be efficiently implemented on data sampled on a square grid? I'm referring to an ideal filter with a spatial ...
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29 views

Negative Exponential Filter SciPy

I'm trying to transform a time series with a recursive filter to model a feedback. I was able to do a simple filter like : ...
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1answer
21 views

How to draw the magnitude plot of a variable slope low/high pass shelving filter? (eg. as a function of cascaded shelving filters)

I am interested in making a magnitude graph of a variable slope low/high pass filter. I would like to set slope in dB/oct and a cutoff pitch. The y-axis should be amplitude from 0 to 1, and the x-axis ...
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Real time signal smoothing / high pass filter

I am attempting to effectively high-pass a signal sampled in real time at 10kHz, to remove frequency components <= 1 Hz with minimal distortion (due to phase/group delay) of the signal components >...
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Notch Filter with given Bandwidth

I have to use Matlab with the iirnotch()-function to design a notch filter. The notch should sit at 520Hz, the Bandwidth should be 100Hz and I have a sampling ...
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1answer
28 views

Reduce noise from wav audio

For a didactic project we need to split an audio file with a phrase into words. For this purpose, we need to identify the silences in the file and labeling the audio where there is a voice activity. ...
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34 views

Why is Cheby 2 filter uncommon?

I've been reading the Chebyshev filters chapter in The Scientist and Engineer's Guide to Digital Signal Processing and it says "The Chebyshev filters discussed in this chapter are called type 1 ...
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1answer
43 views

Overview Noise Reduction Techniques

I am trying to learn signal processing and when I research about ways to reduce noise in different situations it's so easy to get lost in one solution or go down the wrong path for example, is your ...
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How to Combine / Cascade two `3 x 3` Filters into One `5 x 5` Filter

If you have a uniform 3x3 box filter T which is: 1 1 1 1 1 1 1 1 1 And an 3x3 laplacian filter W which is: 1 -2 1 -2 4 -2 1 -2 1 Can these 2 filters be combined into one 5x5 filter, the ...
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High quality removing gravity from accelerometer data without Sensor Fusion

My smartphone have only accelerometer sensor. I need to get data close to (0,0,0) in hold in my own application. I did use some app from Google Play and data was very close to it (some like 0.1 and ...
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41 views

Implementing Edge Preserving Diffusion (Anisotropic Diffusion)

I am trying to implement edge preserving diffusion. Recall the general diffusion equation to be: $$\DeclareMathOperator{\Div}{div}\delta_t u = \Div(g \nabla u)$$ Where $g$ is the speed of the ...
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What filter is optimal for noise cancellation when working with very low sample count

I am working on sound processing android application project in which I have to input sound and remove noise as much as possible at run-time, somewhat like streaming. I am recording video at one place ...
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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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From Laplacian of Gaussian filter back to original signal

Given a Laplacian of Gaussian (LoG) filter of a signal, how can I reconstruct the original signal? Usually LoG filters are used for images. In my specific case, the filter is instead applied to a one-...
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1answer
34 views

Inverse Fourier of Two-Pole Transfer Function

I would appreciate if someone could walk me through this derivation. I have a transfer function in the frequency domain, which has two poles $$\tilde{H}(\omega) = \Big(\frac{1}{1 + i \omega \tau_1}\...
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What does the order of a bandpass filter specify?

Let's assume we have a digital bandpass filter. Which parameters of the filter are affected if we change its order? If I am not mistaken, when we increase the order of the filter the transision ...
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How to filter ECG and detect R peaks

I am trying to extract R peak from raw ECG data and some samples are seemed to be interfered by EMG. I used the lib provided by biosppy with python, biosppy.signal.ecg, it seems that the lib does, ...
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2answers
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Hyperbolic sine “sinh” in fixed-point?

As part of an audio peaking filter calculation, I need to implement hyperbolic sine ("sinh") function in a fixed-point arithmetic (fixed-point DSP processor). What is the proper way to do this?
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Is the convolution between a decomposition and reconstruction filter a scalar?

I'm very new in a research topic about wavelet filtering and I received an observation by a professor, but I actually cannot understand it, so I ask you to help me. Suppose to perform a stationary ...
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33 views

How draw the frequency response

I'm learning signal processing on my own and I'm in the filters, I chose the moving average because it seems the simplest. What I want to know is how to draw the frequency response of the moving ...
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23 views

what should the the output of an FIR filter (root raised cosine) look like?

I am implementing a filter that is FIR on verilog HDL ,, I understand what happen in the filter well, I mean the delay, multiply and sum, the problem that I can't imagine how can I get the desired ...
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17 views

How to get the amplitude output of a single frequency from a Resonant Bandpass? (ie. Using a reso BP as an envelope…)

A resonant bandpass like this: is resonating at a frequency of 125 Hz. You are controlling the decay time by modulating $Q$ accordingly. The BP is being excited by a MIDI triggered impulse. At its ...
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Using Wiener filter to recover original signal

I have a power spectrum of random field $$P(k) = \text{const} \times \exp{(-r_1 \times |k|/2)}$$ and its normalized so $\sigma^2 = 1$, the field had been smoothed by gaussian kernel $$ g_s(k) = \exp{...
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1answer
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Cascading conventional filter with matched filter

The most upvoted answer to this question suggests to use a "conventional" filter in cascade with a matched filter to first remove out of band noise (with conventional filter) and then optimize signal ...
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Concept of scales in Gabor filter

I've been reading about Gabor filters, and there is a concept of scale. While I understand that Gabor features help in analyzing both the frequency and orientations of an image, what is the idea of ...
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Is it possible to create a causal filter with a positively-sloped phase response?

I am currently prototyping a set of noise-cancelling headphones that utilize active EQ to modify the noise-cancelling signal, allowing the user to modify the frequencies that they hear or don't hear. ...
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1answer
67 views

Recursive filter with truncated polynomial impulse response

How can we recursively implement a causal discrete-time truncated infinite impulse response (TIIR) filter with an arbitrary truncated polynomial impulse response: $$h[n] = \begin{cases}\displaystyle\...
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derivative filter for computing speed from robot rangefinder

I have a laser rangefinder on my robot and I need to compute the speed of the detected object. I have seen many different filters for that, but all of them apply only to offline data, or introduce ...
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1answer
19 views

Plane Settings of the Matched $z$-transform Method

I've come across that the matched $z$-transform maps poles of the $s$-plane design to locations in the $z$-plane. My question is, what is the $s$-plane and what does this mean? I'm aware that the ...
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Comparison Between Mahoney Filter and Kalman Filter in Euler Angles (Yaw, Pitch, Roll) Estimation

What are the advantages of Mahoney Filter over Kalman Filter for Euler Angle (Yaw, Pitch, Roll) estimation? Could anyone compare them for Angular State Estimation? Resources Mahoney Filter ...
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1answer
23 views

What is the name of this filter?

I am having this simple function which acts on two state variable $s_t$ (states being $\{0,1\}$, boolean in sense), and I am evaluating it in discrete time steps. The function is $f_t=1$ if $s_t$ has ...
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1answer
44 views

Odd-order Butterworth filter gain at cutoff frequency

Wikipedia gives the gain of an n-order Butterworth filter as $$G^2(\omega)=\left |H(j\omega)\right|^2 = \frac {{G_0}^2}{1+\left(\frac{j\omega}{\omega_c}\right)^{2n}}$$ here. If you look at the gain ...
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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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1answer
32 views

How Could I extract the signal in the below Image

This is my first post so sorry if I make any mistake. The entire signal length in the screen shot below is 10 second. I ran a first order low pass filter (digital) at 10Hz cut-off frequency, and I ...
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1answer
24 views

Automatically crop out certain region around red objects

I have the image seen below and I would like be able to automatically crop out everything around each red section - not enough to overlap but enough that you can see how connected to the green parts ...
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1answer
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Overshoot when using Bessel filter

Here is simple code to illustrate overshoot using bessel filter: ...
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finding harmonics from fundamental

https://s3.amazonaws.com/izotopedownloads/docs/rx700/en/interactive-tools/index.html#selection-tools From the above link, under the "Magic Wand" tool description, how does that algorithm work? In RX,...
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how to calculate a SNR?

i had some question.i have do some some filtering FFT using a matlab program.but,i need to compared the original signal,noise signal,and filtering signal based on SNR.but i dont understand how to ...
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1answer
34 views

Reading a Wav File [closed]

I need to read two .wav files. One of them is a song, and the other one is impulse response. Then, I have to convolve them. In fact, I have read them by using ...
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1answer
41 views

How is the Gaussian kernel related to the Euclidean distance of the neighbourhoods in the non-local means algorithm?

I am reading the paper A non-local algorithm for image denoising that describes the original non-local means algorithm. They define (p. 3 of the pdf) the distance between two square fixed ...
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2answers
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Why can convolution only be applied to compute the output of a linear filter?

We apparently cannot compute the output of a bilateral filter (BF) using convolution (with the image) because the BF is a non-linear filter. In general, why can convolution only be applied to compute ...
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1answer
22 views

How does the power spectrum of the amplitude envelope depend on its underlying carrier frequency?

when looking at the amplitude envelope of an oscillation (see red trace in Figure below), it seems to me as if the frequency content of the envelope depends on the the frequency of the underlying ...
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2answers
61 views

Delay in Savitzky-Golay filtering

I am applying a Savitzky-Golay filter to a signal, using the scipy function. I need to calculate the lag of the filtered signal, and how much is it behind the original signal. Could someone shed ...
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Is the WTST-NST filter available as a module in some python library?

I need to implement the WTST-NST filter (wavelet transform based stationary non-stationary filter) to denoise some sound files (preferably in Python). I am from a Mechanical Engineering background ...
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2answers
80 views

Why isn't bilateral filtering shift-invariant?

I have a source (that I can't share) that states that bilateral filtering isn't shift-invariant (that is, it depends on the input signal), hence we cannot use convolution and the Fourier convolution ...
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2answers
62 views

Convolution of Two Impulse Signals

I have encountered convolution of two different impulse signals. ...
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11 views

Frequency warping while creating filter coefficients

If I have an audio signal at 16kHz with frequencies band-limited to 8kHz. I want to low-pass filter this signal such that fc=4000Hz. Meaning when I reconstruct the signal I do not want any content ...
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How to implement separable bilateral filter?

I’m trying to optimize my naively implemented O(n^2) bilateral filter for 2D images. I googled and found a lot of theoretical explanations about the separate one. However, it seems there are things ...
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1answer
23 views

Biquad Filter Non-Linearity

I'm using a biquad filter algorithm in my project. I got 3, 16 size variable arrays summing into one and then gets filtered. Now i want to filter each array seperately and sum after that, which if ...
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1answer
41 views

How to characterize this whitening filter?

A little bit of background: I am interested in whitening in the least-square estimation. In this sense, consider a univariate signal $y$. Assuming the covariance of $y$ is $\mathbf{A}\sigma^2$. ...