Linked Questions

1
vote
1answer
27 views

FFT/PSD/IFFT analysis on single axis piezoelectric accelerometer signals for curb impacts

I'm trying to denoise the signal by performing PSD analysis and followed by IFFT. Ultimately, I want to generate Force and Displacement plots from the denoised acceleration signal. Noisy Acceleration ...
1
vote
2answers
32 views

Time Series processing using fft

I have a set of real data (timestamp and value) with an unstable step between samples (5sec, 30sec etc.). The data is the % of fillage of a vehicle's tank through time. Due to the harsh volatility of ...
1
vote
1answer
43 views

Using DFT Rotation for Frequency Down-Mixing

Is it possible to perform Frequency Down-Mixing (sometimes referred to as Down-Conversion) by simply rotating the DFT sequence? If so what are the Advantages and Disadvantages of this method?
0
votes
0answers
39 views

How can I generate an ideal 2D low-pass filter in MATLAB?

I've been tasked with creating a 32 x 32 half-band low-pass image filter in MATLAB. My thinking is to generate the ideal filter mask in the frequency domain and compute the corresponding convolution ...
0
votes
2answers
31 views

filtering difference b/w freq and time domain

When you want to get the specific frequency (ex. around 1000Hz), you might take FFT, remain the frequency you want, and reduce the power of the other frequencies you do not. ex.) if fs=16khz and ...
0
votes
0answers
61 views

FFTW audio artifacts when modifying magnitudes in frequency domain

I'm currently working with FFT (FFTW3) that I'm using to apply treatments on audio files frequencies. The Forward/Backward test is passed, since I can get the exact same soundfile when processing ...
1
vote
2answers
96 views

Question about ideal filters

Following shows the discrete time Fourier transform of an ideal low pass filter with cutoff frequency $\omega_c$: $$H\left(e^{j\omega}\right) = \begin{cases} 1, & \text{if $|\omega| \le \omega_c$...
0
votes
1answer
84 views

Is resizing of frequency spectrum a valid method of resampling?

One method of resampling is to perform a Fourier Transform on a signal, resize the resulting frequency spectrum, and then return to the resampled version of the signal with an inverse fourier ...
0
votes
1answer
46 views

Find signal power in a band by integrating the PSD in a frequency band (and zeroing the out-of-band DFT bins)

I know that directly zero DFT bins outside a frequency band has the side effect of introducing ringing, as this post says Why is it a bad idea to filter by zeroing out FFT bins?. But what about ...
1
vote
2answers
51 views

Digital filtering based on frequency component amplitude… why not?

I've got a very general question. I've just implemented a filter working in frequency domain that simply cuts every frequency component whose modulus amplitude falls below a certain threshold value. ...
0
votes
1answer
50 views

Downsampling - how many extra samples to include

I want to downsample a finite section of an equidistant time-series $$x_i, \qquad i=0\dots n-1$$ by doing an FFT and dropping the upper part of the spectrum. Since the FFT looks at $x_i$ as a cyclic ...
1
vote
1answer
307 views

Building a FIR filter from an arbitrary frequency-magnitude response curve (eg. Least Squares fitting) [duplicate]

I'm trying to create a FIR filter from a magnitude equation, where my starting equation provides the magnitude (amplitude) between 0 and 1 for any given frequency in Hz. I posted the magnitude ...
1
vote
2answers
91 views

Time domain to frequency domain conversion of audio signals to extract 1/3 octave frequencies

I am writing first time in this forum and I am not expert in programming and FFT. We have developed an android app (Noise Tracker) for noise measurement using smartphones. It displays noise levels in ...
0
votes
1answer
117 views

How many things can they be done with a spectrogram?

I found some things that can be done with a spectrogram. filter frequencies by setting the bins to zero observe what frequencies make up the signal. observe the energy or amplitude of each frequency, ...
0
votes
3answers
54 views

Filtering using fourier series

Suppose I have a measured signal $M$ that has frequency components from 0 to 50 Hz. I plot the specturm of this signal using FFT and I observe its frequency content (power vs frequency). Then, I ...
0
votes
2answers
658 views

How do Anti-Aliasing Filters filter the signal?

I have programmed a anti-aliasing filter that uses the fourier-transformation and makes a perfect cutoff on my desired cutoff frequency for downsampling without aliasing. I have read about other ...
0
votes
0answers
30 views

Use Cases of FFT in Signal Processing [duplicate]

I am trying to learn about signal processing and fft's applications within it. My understanding is that a classical use case for fft is to remove "noise" (ex. high frequencies that are not supposed to ...
0
votes
1answer
55 views

Reducing one frequency in song

How would I take a song input and output the same song without certain frequency ranges? Based on my research so far, the song should be broken down into chucks, FFT it, reduce the target frequency ...
1
vote
2answers
2k views

Difference between bandpass filter and using fast fourier transform to extract power of frequency bands

In signal processing, I have heard of two terms: Using band-pass filter to extract some frequency bands. Using Discrete/Fast Fourier Transform (DFT/FFT) to extract some frequency bands. Are these ...
0
votes
2answers
54 views

Extracting different frequency bands (alpha, beta, gamma) from brain activity data

I am new to signal processing and despite googling about my question, I still couldn't find the solution. I have an Electrocorticography (ECoG) dataset. This consists of recording brain activity from ...
0
votes
2answers
401 views

Fourier transform of a noisy signal

Let's suppose i have a sensor that measures the output of a process and this cause a not negligible noise that affects my signal. My goal is to analyze the process signal in order to find faults. How ...
0
votes
0answers
54 views

FIR Filter Magnitude Response

This is the shape of the bipolar amplitude function for a FIR filter with odd m: I have 2 questions : If i want to use this FIR as a low pass filter between 0 and $\frac{F_{c}}{2}$ , how can i set ...
1
vote
0answers
51 views

My X ray images have black background, which turn gray after low-pass filter. How to recover blackness?

I am applying a low-pass filter to X ray images, which changes the pixel distribution such that the background goes from black to gray. In the attached figure, this amounts to the mode increasing from ...
1
vote
1answer
1k views

Complex output after inverse FFT of a real signal

I have a real one dimensional signal s (light absorbance in a flow cell), which has significant noise and some periodic noise after performing a deconvolution of $S$ from $S_o$. Basically fft($S$) was ...
0
votes
1answer
55 views

Advantages of the Rotation Translation Operation Before Doing FT Smoothing

I was reading a relatively old paper from the 1970s on smoothing by FT methods (chemistry applications), where the authors show that if we do rotation translation operation on the signal (y- values) ...
0
votes
0answers
29 views

Is it possible to recover the time-domain signal after manipulating it in the frequency-domain? [duplicate]

I've worked a fair amount with EEG signals, though I've never had formal training in signal processing, so please excuse my ignorance. The problem is this: my signal has noise at many, many ...
0
votes
1answer
44 views

Bringing the signal into the same level [duplicate]

I have a signal, shown in the attachment (blue one). As you can see that the latter part of my signal has a higher dc offset. I want to bring the signal into the same level. I have tried eliminate the ...
0
votes
2answers
158 views

Manually creating a lowpass filter from the frequency domain: what phase?

In an attempt to gain a better understanding of DSP, I want to create a very simple (1D) lowpass, or I think more correctly "stop-band" or "band-reject" filter, to filter out a single frequency, e.g., ...
0
votes
1answer
83 views

What happens if I zero out the initial terms of the fft output and take inverse fft? [duplicate]

I am new to signal processing domain. When I run fft on data of length 1000, I get 1000 complex numbers. Now, if I want to extract the low frequency information or signal approximation, I take the ...
0
votes
0answers
115 views

Where to start in the design of my filter to remove 50 Hz

pick any 3 random files from this database, : https://physionet.org/pn3/ecgiddb/ They are subject to 50 Hz powerline interference. We wish to convert from time domain to frequency domain and remove ...

15 30 50 per page