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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Filter Coefficients in MATLAB are always float data type

I will be using the filter coefficients generated by MATLAB in my code that will run on a microcontroller. The poor microcontroller is very bad in floating point Arithmetic. So What do I do? Shall I ...
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289 views

How can I detect clicks/ticks in a wav file?

I have a long recording of a train (here is a small sample) there are a number of clicks as the wheels go over joins in the tracks. I would like to detect the location of these. Looking at the ...
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331 views

Adjustable Notch Filter help

I'm converting the simulink diagram found in this paper to C code. I'm not familiar with matlab/simulink(too expensive) so need help interpreting the diagram. The problem I experience is that once a ...
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How can a filter have zero group delay?

If you put a wave packet through the passband of a 1st-order low-pass filter, it will be delayed by the group delay of the filter, and remain the same amplitude, right? If you put the same wave ...
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1answer
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Can the Walsh Hadamard transform be computed for non power of 2 sizes?

Can the walsh hadamard transform be calculated for odd image block sizes such as 5x5 or 7x7? Most of the examples I've seen are for 4x4 and 8x8? I fear it probably can't from the description I read ...
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Calculating a filter's attenuation at a certain frequency from the Q-factor

I'm using the Web Audio API to make a graphic EQ with four BiQuad filters; a highpass, two bandpass and a low pass: You can see each node representing each filter's frequency. It's working nicely but ...
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could anybody explains me why IIR filters do not have linear phase?

Please tell me. Also I dont know why phase is linear with FIR filters. I would like quantitative analysis. And why linear phase is not achieved by IIR filters ?
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1answer
129 views

What is mean by [1 -1] Filter?

While studying about Wavelet Transform, I'm confused as why this is called a [1 -1] Filter , Here is what i'm talking about. In this hypothetical example the student does fairly well the first ...
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1answer
305 views

How do I start studying Gabor Filters ?

I know very basic image processing. Please suggest me how do I and where do I start learning Gabor Filters ?
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Difference between 'conventional' and 'adaptive' beamformers?

This might be a terminology question but I am not sure. Basically, what is the difference between conventional beamformers, and adaptive beamformers? I thought that all beamformers were inherently ...
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Determining Type and Bandwidth of a filter

Given a filter, if it is given as an equation such as: $$f(x,y) = \left(\frac{\partial^2}{\partial x^2} + \frac{\partial^2}{\partial y^2}\right) \exp\left(-\frac{x^2 + y^2}{\sigma^2}\right)$$ Or in ...
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1answer
117 views

How to calculate signal which is not changed by a filter?

Suppose that there is a FIR filter F and a signal S. The filtered signal is the convolution of F and S, F * S. The problem: how to calculate a signal S' such that F * S' = S' (the filtered version ...
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Cut off frequency for low pass filter

Hi I am trying to use a low pass filter in Matlab. I am trying to use the simple butterworth filter. I have defined dataset say "data". Then I created the butterworth filter as follows: ...
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4answers
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How should one select this filter coefficient for a pre-emphasis filter?

My professor asked me why you choose $a=0.97$ in a pre-emphasis filter $H(z)=1-\frac{a}{z}$ for your pre-processing step. What is the relation between $a$ and the filter? How does this coefficient ...
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0answers
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Smoothing data from a 3D camera

The camera uses two cameras and reflective infrared markers to compute 3D positions. For recognized marker configurations, the camera computes a translation and an orientation (quaternion). For stray ...
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4answers
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Why does OFDM use cyclic-prefix while QPSK uses root-raised cosine filters?

My understanding is that BPSK/QPSK/... are often implemented with root-raised cosine (RRC) filters to reduce ISI and bandwidth. OFDM can be understood to be BPSK/QPSK/... implemented on multiple ...
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1answer
595 views

Intersymbol Interference — Root raised cosine filter redundant if doing impulse response equalization?

I'm implementing DBPSK (differential binary phase-shift keying) over audio (44.1kHz sample-rate) using software. Eventually I'll use multiple audio frequencies at once, so I'm using FFTs and inverse ...
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0answers
118 views

Recover High Frequency Loss in a Simulated Power Spectrum

I'd like to ask a theoretical question about power spectra. In MATLAB, by means of a particular approach, I'm trying to generate a Gaussian variable which embodies a particular power spectrum. The ...
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how to extract telephone audio only from an mp3

I have mp3s of radio talk shows in which the host interviews people on the phone. The host uses a microphone, and the interviewee uses either a landline phone or a cell phone. I want to save just the ...
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1answer
174 views

reduce harmonics produced by microcontroller

I'm generating an 18kHz sine signal using a dsPIC microcontroller at 44100kHz (I'm not sure I can call it sampling rate, maybe generation rate, although the concept is the same). The dsPIC's DAC then ...
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148 views

Local signal-to-noise ratio for an image

I want to do one of these common experiments to see the effect of increased noise on the performance of a feature detector. To do this add zero mean gaussian noise with fixed sigma to the image and ...
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3answers
621 views

Recover Filter Coefficients from Filtered Noise

I have a digital signal which may be represented as a pulse noise source filtered with an FIR (finite impulse response) filter. Suppose that the noise consists of discrete pulses (nonzero samples ...
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2answers
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Eliminate Signal A from Signal B

i have 2 audio signals, both available in time and frequency domain: A: Noise B: Noise(A with minor variations) + Additive sounds (C) i want to eliminate Signal A from B to leave only C. C is for ...
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278 views

Filter for Reducing Background Noise in Image

I have images where there is a lot of "black" background (few shades of black). (In many images at least half the pixels are background). I need to get interest points from the image, but because the ...
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1answer
626 views

How to Obtain Mathematically High Frequency and Low Frequency Component Separately Using Bilateral Filter?

I have asked this question before in the sense that what does a high frequency and low frequency component signify in a image and i got satisfactory answers now i want to know that how i can get high ...
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How to Extract High Frequency and Low Frequency Component Using Bilateral Filter?

What does High frequency and low frequency component signify in an image. How to separate out the high frequency as well as low frequency component of an image using Bilateral filter.
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264 views

Implementing IIR filter using FSM

How do I implement an Infinite Impulse Response (IIR) filter using Finite State Machine(FSM)? The problem is FSM has finite memory, but an IIR filter has infinite outputs. The closest match is this ...
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4answers
14k views

Interpolation with an FIR filter

How can I use interpolation with an FIR filter? I am more familiar with interpolation such as nearest distance interpolation, linear interpolation and so on. Suppose a signal is given as the ...
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1answer
2k views

Blurring Non-Uniform Areas

I have an image with arbitrary area (the boundary is shown in gray): I would like to blur just the image within boundaries. Ordinary blur causes the background proliferating to image and vice versa. ...
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1answer
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Online filter for EEG

My goal is to build a real-time filter for EEG data. The data are being recorded in 512Hz and I wish to filter it (in a real-time, from 0.5Hz to 30Hz in the most optimal way). Unfortunately I'm not ...
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1answer
189 views

Are there any filters that look (vaguely) like this?

I'm trying to determine the effect of a particular non-linear process on my data. From simulations, I can measure the power spectra of "ideal" and "processed" images and take their ratio, which (I ...
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3answers
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Determining what filter (if any) has been applied to an image

I'm trying to determine what "filter" has been applied to an image. I have the original, raw image and the processed image. The processed image has been put through a pipeline (black box) that does ...
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1answer
212 views

A filter for for a realtime system?

Apologies if this is too basic. I need to implement a band-pass filter, for a realtime system. Not sure what to use. FIR? IIR? Something else ? Any tips would be highly appreciated.
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FIR design : compute coefficients for the same frequency response at another sampling frequency

I would like to know if there's a standard way to obtain the FIR coefficients for a sampling frequency $F'$ when the coefficients are for a sampling frequency $F$. I would like to implement the ...
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3answers
4k views

Weight vector of an exponential moving average?

With weight vector I mean the vector with weights that you have to multiply the observations in the window that slides over your data with so if you add those products together it returns the value of ...
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2answers
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Understanding the Parameters of the Bilateral Filter

Allow me to show you a snip from Szeliski's Computer Vision book on bilateral filter. I don't know how to interpret these kernel definitions: In the actual summation what values do the $k$ and $l$ ...
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1answer
2k views

Producing Colored Noise from a given PSD Data

I need to estimate (extract/produce) the colored noise of a given PSD Data. I have the following procedure to get the desired results. First of all I calculate the filter coefficiencts using firls ...
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Why is it a bad idea to filter by zeroing out FFT bins?

It's very easy to filter a signal by performing an FFT on it, zeroing out some of the bins, and then performing an IFFT. For instance: ...
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1answer
434 views

Ultrasound pulses and reflection problems

I am building a whiteboard to track the position of its pen. I have n ultrasound receivers placed on the periphery of the whiteboard, and an ultrasound emitter in ...
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1answer
644 views

Audio Signal Noise Filter Problem

I'm currently working with audio signals and have a problem: C = A*B + N, where C = recorded signal from microphone consisting of: A = known music file data played on speakers next to microphone ...
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3answers
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What is the ideal FIR length, given a specific pulse length?

I am trying to ascertain what the 'ideal' FIR filter length should be, given the pulse length $T_p$ of a windowed sinusoid in noise that I seek to filter. As parameters into an FIR filter that I ...
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1answer
126 views

Vestigial Filter problem?

I have been stuck on this question for a while now. It has to do with vestigial sideband. I wasn't sure if I should be dividing $H(\omega)$ graph values by 2 because only the positive side of the ...
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3answers
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Adding noise to an ECG signal

I am doing a project on ECG arrythmia analysis using matlab. I have designed notch filter for removing 50 Hz noise but don't know how to add a 50 Hz powerline interference noise to a clean ECG signal?...
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1answer
309 views

Determining the type of filter on an image

I have the following mask where the origin is marked in bold text $$ \left[ \frac{-1}{4}~~~{\bf\frac{1}{2}}~~~\frac{-1}{4} \right ] $$ After computing the DFT, the result is: $$ \frac{1}{2} - \frac{...
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Recover myself from Dilate and Erode for noise reduction

i have obtained some skin detection map (i post below two example of detection map). but, i'm using a normal webcam and the map is noisy. Not a lot, just a bit. I think i can remove noise only with ...
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1answer
470 views

What is a Phase Delay filter?

I'm looking at a job spec, detailed below. I'm perplexed as to what is being asked for. Could someone offer a basic understanding of this material? I can imagine a solution may involve performing ...
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1answer
214 views

Effective filter with small tap size

I am dealing with a problem where I need to make a decision on a 500khz signal under 100usec. The signal is noisy and I am detecting a peak in the incoming signal. Currently I do a 7 step mean filter ...
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2answers
135 views

Lightweight audio listener for detecting blip

The challenge I'm looking at is to design an iPhone component that listens to microphone input and triggers when it hears a particular blip (preferably < 0.1sec duration). I can design the blip ...
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1answer
111 views

Is there a transformation filter to decode light signal through Glass Bricks?

A friend is doing renovations and getting his entire ground-floor street-side wall replaced with glass bricks. I told him that with all those bricks giving similar distorted views of the same room, ...
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1answer
269 views

Applying a Filter Kernel Defined by a Continuous Equation in the Frequency Domain

I have a filter kernel $K(\omega)$ completely defined in the frequency domain as a continuous function of angular frequency $\omega$. I know $K(\omega)$ defined as a continuous mathematical equation. ...