Questions tagged [filtering]

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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, so I need concrete answers ideally ...
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2answers
440 views

Optimal Level of wavelet decomposition for denoising

If a certain mother wavelet is defined and the optimal threshold shall be defined via Donoho, how can I define the optimal decomposition level to achieve the best denoising results.
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1answer
467 views

Analytical expression for step response of digital bessel filter

If I apply a digital Bessel filter to a perfect step function, I get something that looks like the following: The green line is the input step response data sampled at 500kHz, the red line is ...
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1answer
456 views

Bandpass filtering an audio signal with MATLAB's $\tt kaiserord$: unknown new frequency component

I am trying to filter an audio signal with kaiserord in MATLAB, but I'm having a problem. Here is my code: ...
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1answer
155 views

Extracting narrow-band ZigBee signals(4 MHz) from a wide-band WiFi signal(20 MHz)?

I am planning the following. First sample the 20 MHz WiFi channel (WiFi channel-1 in figure). Put band pass filters (5 MHz wide) around each of the ZigBee center frequencies (11, 12, 13, 14). Re-...
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3answers
721 views

How do I eliminate line noise from USB microphone

I'm trying to record voice from a microphone into my laptop. Unfortunately, the laptop does not have a microphone jack, so I have to use the USB input. This doesn't present a problem when I record ...
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4answers
229 views

Understanding the lowpass filtering of a digital signal

I do not have any background in Electrical Engineering and I have recently started a project which involves signals captured from sensors. Lowpass filtering: The way I understand it is: The values ...
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3answers
147 views

How to filter key clicks?

I am the author of an amateur radio application that produces a waterfall display across a range of frequencies. Time is on the $x$-axis, frequency is on the $y$-axis, and the relative strength of ...
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1answer
3k views

How do we use signal::filter and signal::butter in R for EEG data?

I am trying to design an experiment to determine the peak amplitude of an EEG signal in response to a stimulus. Till now, our team has been using MATLAB and since we wish to go open source, we are ...
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1answer
2k views

What is the significance of Butterworth filter in image processing?

Filters like mean,median,gaussian,bilateral and adaptive forms of these filters are used commonly in image processing but not Butterworth filter. The reasons I could think of are a) Butterworth ...
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2answers
135 views

How is Bayesian Estimation related to filtering?

I am reading about estimation theory, including topics like Bayesian Estimation (e.g. Wiener Filtering). It seems that we usually define a filter in terms of tis frequency response (e.g. High Pass, ...
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2answers
755 views

Practical examples of ARMA model

I am studying the Kalman filter and its basic implementation, and it was asked to use the filter to estimate a signal observed in noise $$y(n) = x(n) + v(n)$$ where $v(n) \sim \mathcal{N}(0, \sigma^2)$...
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0answers
261 views

Prediction-error filter for images

I am interested in studying local pixel value dependencies in images and I am wondering if it exists a general form of prediction-error convolutional filter that is able to suppress the image's ...
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1answer
518 views

Wiener filter to estimate constant signal

I want to compare the performance of a Wiener Filter and the Kalman filer to estimate the value of a constant $d$ using mesurements corrupted by a white noise. That is, my measurements are of the form ...
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1answer
2k views

Interpolating/Decimating CIC Filter Group Delay

I have an Interpolating Cascaded Integrator Comb (CIC) filter designed as so: Rate Change = 100 Number of Stages = 4 Differential Delay = 1 I'd like to calculate ...
2
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2answers
136 views

Equalizing frequency response in software

I'm playing audio through a speaker which I know to have a non-flat frequency response, with particularly poor response in the low ($<1\textrm{ kHz}$) ranges. My plan to get around this problem is ...
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2answers
236 views

Easy way to get rid of noise in a hand drawing

I would like to take a user's hand drawn input, and filter out "noise", aka small sketches or blobs, where the user might have screwed up and accidentally touched his hand to the drawing device, or ...
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1answer
663 views

Filter and crop an image

I am a big fan of fft convolution. So, I mostly try to avoid non-fft convolution. Suppose, I am trying to convolute an image with another image. Suppose the first image is $512\times 512$, and, the ...
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2answers
1k views

Smoothing a staircase

I have some data from a position encoder, so naturally i want to estimate its speed. However, the data is very quantized, so it's difficult to smooth enough to differentiate easily: Each step level ...
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0answers
29 views

How do I smooth-over transition from a time-series generated by one system to a time-series generated by another system?

So I have generated a time-series with length on 2N samples, where the first N are generated by one auto-regressive system and the N+1 to 2N are generated by another, similar, auto-regressive system. ...
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2answers
4k views

Root mean square bandwidth of a signal with flat spectrum

I am trying to derive a simple expression for root-mean-square bandwidth $B_{\rm rms}$ for a signal that has flat spectral density over its entire bandwidth $B$. The expression for the $B_{\rm rms}$ ...
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2answers
696 views

Convolution to do FIR with initial and final conditions!

I need to apply an FIR filter on chunks of very long signals. I can use MATLAB's filter function as follows to preserve the state of the filter when a new chunk of data is available: ...
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1answer
246 views

Shock filtering using structure tensor

my name is niladri, I am new to image processing(actually this is my first code). I want to implement shock filter using structure tensor. I have rough idea of what structure tensor is and implemented ...
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1answer
1k views

Smoothing a power spectrum

My question is regarding how one could/should smooth a rather noisy power spectrum obtained from measurements. There are various methods one can use (a moving average, binning, etc) and I am not sure ...
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1answer
114 views

Do filters work on a “per sample basis”?

I'm confused because of filter length, whether (such) filters can be used to filter audio on a "per sample basis"? By per sample basis I mean that I would like to filter audio one sample at a time, ...
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2answers
479 views

Undoing a filter operation in MATLAB

Out of curiosity, is it possible to actually reverse a filtering on MATLAB. For example, if I have ...
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3answers
218 views

Adaptive filter with two inputs

I have general theoretical questions: Is it true that an adaptive filter with two inputs (one normal and one delayed by the single time increment) can completely get rid of any single frequency ...
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1answer
794 views

What are the advantages of higher order Kalman Filters like EKF, UKF?

Kalman Filter provides the optimal estimate of the states of a stochastic dynamical system if the system is linear, the measurements are also linear functions of states and the errors in system ...
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1answer
747 views

Causal and Non-causal filtering. Strange behavior

I'm trying to understand the behavior of a causal filtering exemplified by figure below. This behavior is making LDA (Linear Discriminant Analysis) misclassify our data, by clearly reverse the signal ...
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2answers
99 views

What criteria should be used for smoothing

Actually I have some measurement which I want to get rid of noise I want to use different filter techniques but I am wondering what criteria I should use to check if I am removing noise or not or if ...
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1answer
122 views

How can a signal have two maximum frequency components?

$x(t)$ can be exactly reconstructed from its samples at $\omega_s = 10 \textrm{ rad/sec}$. My conclusion is that the maximum frequency component in $x(t)$ is $5\textrm{ rad/sec}$. But I'm being told ...
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1answer
127 views

A question about sampling theory

Let`s say I have a signal $m(t)=\cos(4\pi t) + \cos(6\pi t)$ so we can say the signal is containing frequencies $f_1= 2\mathrm{Hz}$ and $f_2= 3\mathrm{Hz}$. The cut-off frequency of the low pass ...
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1answer
2k views

Choosing correct filter parameters for IMU sensor datas

I have a IMU sensor breakoutboard using ITG3701, LSM303D LinkProduct. This involves accelerometer, gyroscope and magnetometer. I have connected the sensors to a Arduino and sending the datas to ...
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2answers
129 views

In fourier space, how to apply transfer function with n frequencies to input data with m>>n frequencies

I have a transfer function in Fourier space with $N=2028$ frequencies $(\frac {0, 1}{(N\cdot dx)} \dots ) $ Where $dx = 0.1m$. I need to apply this transfer function to a signal with 20000 samples (...
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1answer
121 views

iZotope RX's FFT processing?

How does iZotope RX handle the FFT (i.e. how does it manage to perform those processes in the frequency domain without creating glitches) since its able to e.g. Apply another DSP process (even time-...
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2answers
375 views

Filtering Frequency Bands Out of a Signal

Let's say I have a 2 second data set taken at 220Hz sample rate and I would like to filter out the frequency bands associated with the EEG Spectrum: $$\begin{align} \Delta:& [1,3]\text{ Hz}\\ \...
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0answers
81 views

maching convolution filters to results

I am practicing for an exam and I need help in the following question (it is just for me- no grade...) we get an input image, 6 convolution filters and 6 results. we need to find the matches between ...
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0answers
42 views

Proximal operator of image Laplacian

Let $\alpha, \beta > 0$ and $\Delta := \nabla^T \nabla$ be the discrete laplacian operator, $$\nabla: \mathbb{R}^{n_x \times n_y \times n_z} \rightarrow \mathbb{R}^{3 \times n_x \times n_y \times ...
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2answers
585 views

Filtering noise from FFT, where noise is known to be shifted delta function

I have an input sequence $x=\{x_1, x_2 , ... x_n\}$ of reals, where $n=2^m$ for some $m$. I wish to calculate FFT of $x$. $X=FFT(x)$ However, before I calculate the FFT, the signal $x$ gets ...
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1answer
149 views

Pulse shaping and Baseband filtering

I'm slightly confused about baseband pulse shaping. Let's assume I have a complex data vector in an arbitrary complex constellation (QAM for example). I would like to pass this complex vector through ...
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2answers
2k views

How to filter almost periodic noise?

I have signal that looks like this: As you can see there are some almost periodic pulses at the background with amplitude about 1000. I am saying almost, because, if you zoom in, you may see that ...
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0answers
137 views

Open source GPS+IMU sensor fusion?

Are there any Open source implementations of GPS+IMU sensor fusion (loosely coupled; i.e. using GPS module output and 9 degree of freedom IMU sensors)? -- kalman filtering based or otherwise I see a ...
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4answers
595 views

Removing Bounded Noise from an Audio Signal

I'm currently trying to remove some noise from a "contaminated" audio file. From what's given, I know that the noise is isolated to a specific frequency band - that is, from ~1400 Hz - ~1800 Hz. The ...
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2answers
1k views

Median Filter for salt and pepper noise removal

Why median filter is considered as good for removal of salt and pepper noise? What are the other filters used for the same?
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1answer
315 views

Overlap/Chunk processing possible with Zero-phase?

I'm relatively new to DSP and I'm currently investigating FIR filter and IIR filters. From what I've found FIR filters can be implemented efficiently using the overlap-save method, but I was wondering ...
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0answers
1k views

Implementing a 2d butterworth filter for image processing?

I am at the moment trying to implement a bandpass butter worth filter which i then can use to apply on my original image. Problem is though My implementation of it using OpenCV doesn't seem to be ...
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1answer
57 views

Why Would Pre Filtering Measurement Data Affect the Least Squares Estimate?

In estimating parameters in a discrete time model I've often seen the use of filters applied to the input data, before its applied to least squares processing. I've been told that the filters are ...
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1answer
2k views

Derive velocity and acceleration from position

I generate random spike data that represent the ouput from a rotary encoder. Here the output of my algorithm: The first plot is position, then velocity and then acceleration. Even though I downsample ...
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1answer
85 views

Filtering performance on Poisson noise with quadratic data-fidelity

We recently performed a work on signal filtering/component separation (sparse signal/trend/noise). The cost function contains: A quadratic data fidelity term, Some smoothed $\ell_1$ terms for ...
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1answer
311 views

How is the ends of a bandpass filtered signal reliable after applying the cosine taper?

A taper function decaying to zero at ends such as a cosine window is routinely applied to the signal before bandpass filtering to reduce end effects. Obviously the window alters the waveform. So, as ...