Linked Questions

16
votes
9answers
25k views

Why do we use window in time domain rather than do FFT modify the spectrum and than inverse FFT

I thought that DSP would be done by using FFT of portions of a signal, modify the samples that result from FFT (since they represent the spectrum of our signal + noise) and remove any unwanted signals ...
16
votes
2answers
7k views

A good mathematical explanation of Gibbs phenomenon

I was explaining to someone how Fourier series work in context of constructing signals that are not everywhere differentiable, e.g. square waves, sawtooth waves, etc. When I mentioned the Gibbs ...
8
votes
2answers
7k views

Which image filter can be applied to remove gridded pattern from corrupt jpegs?

I have around 1,400 jpegs that have been corrupted somehow and have lost the backup images. They all seem to have the same gridded pattern of lines over each (i.e. the gridding does not shift from ...
7
votes
6answers
1k views

Why can't a causal digital filter have an infinitely sharp transition between the passband and the stopband?

In DSP book by Proakis and as well as in this pdf, it is mentioned that practical causal digital filters cannot have an infinitely sharp transition from Pass-band to Stop-band. Why is it so? Can you ...
5
votes
2answers
2k views

Zeroing bins before IFFT

Endolith's recent question on zeroing FFT bins got me thinking about a possible error in my workflow and I'd like to double check. Consider a signal $x_i[m],\ m\in\{1,\ldots,M\}$, i.e. $M$ samples ...
5
votes
1answer
2k views

How to improve an FFT AM demodulator for NOAA APT satellite imagery?

My question involves proper FFT Technique for AM demodulation, in the special case where the modulation rate exceeds the carrier frequency. This question has a specific hobbyist application, the ...
4
votes
4answers
4k views

Removing values from FFT result same as filtering?

I don't quite understand why the textbooks say it is impossible to implement an ideal low pass filter. If I was to take the FFT of a discrete signal x[n], with Matlab's fft function I'd be returned ...
4
votes
3answers
992 views

Chop out frequencies outside human hearing range

I have a bunch of audio files all sampled at 44100 Hz sample frequency. I am trying to remove all the frequencies which are outside the human hearing range (I use the following as reference: Frequency ...
4
votes
4answers
1k views

Removing cyclic noise from signal

I'm using a sensor with output that looks like the following figure. The cyclic noise is common to ask measurements made by the sensor. Is there a way to remove the noise without negatively effecting ...
3
votes
2answers
5k views

Low pass filter with DFT

This is my first question at this site, please excuse me if I'm not asking the question properly. I have an acoustic signal of a test and I want to remove the "thin" peaks, because they don't really ...
3
votes
2answers
44k views

Removing noise from audio using Fourier transform in Matlab

I'm trying to remove noise from an audio file. This audio file contains speech as well as constant pink noise. I know that I have to use the Fourier transform to convert to the frequency domain then ...
3
votes
2answers
1k views

About designing digital filters [duplicate]

I'm currently using MATLAB's fdatool for filter design. Using that tool, I can easily design different kind of filters. For example, let's take a band-pass FIR filter with 10-40 Hz passband, and 5-10 ...
3
votes
1answer
497 views

Remove Noise from Physiological Signals [duplicate]

I have collected a set of physiological signals through emg sensors. I will link at the end of the post an example (10 sec.) of a signal collected on zygomatic muscle. When I analyzed these data, I ...
2
votes
1answer
2k views

simplest Notch filter in the world

What do you think of this notch / band reject filter for a very very narrow band ? ...
2
votes
1answer
159 views

Why bother impluse invariance, bilinear transform?

Now that we can operate in the frequency domain by way of FFT. We can implement ideal lowpass, highpass and bandpass digital filters. then why there many textbooks talk about designing digital ...

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