Questions tagged [frequency]
Frequency in signal processing is the number of cycles (of the signal) per second.
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interpreting wavelet transform of brain siganls
I have created wavelet transform of my signal using the following code:
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7 views
How to find the number of vectors to sample in Compressed Sensing?
When comparing my MATLAB code to a previously written one, I come across the following formula for the number of vectors to sample:
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1answer
33 views
Perform Transposed Convolution in Spectral / Frequency Domain?
I'm doing some experimentation on performing end to end generative modeling in the frequency domain. I've got a working convolutional layer, but do not yet have a Conv2DTranspose equivalent. Please ...
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2answers
68 views
Specify minimum trigger frequency for recording audio in Python
I'm writing a script for sound-activated recording in Python using pyaudio. I want to trigger a 5s recording after a sound that is above a prespecified volume and frequency. I've managed to get the ...
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3answers
105 views
What is really the Mel-filterbank?
After applying STFT to a signal, you typically need to convert the frequencies to the Mel scale. Typically the frequency values range from $0$ to $N/2$, where $N$ is the width of each sliding window.
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2answers
102 views
ELI5: How do biquad filters like bandpass “know” the frequency of a signal?
I understand the code behind biquads, but I fail to understand how 5 coefficients in a biquadratic formula can isolate frequencies so precisely, especially considering it only takes the last two ...
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1answer
83 views
Finding Frequencies from Log Indexed FFT
I have FFT data that has logarithmically scaled at x-axis as shown on the image. But the problem is I do have only array of float numbers that has 1024 element in it, but I know that is already not a ...
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1answer
279 views
Coding an LFO in C
I want to know how I could implement a Low Frequency Oscilator on a simple synth I've coded in C. First in order to understand how to make this happen I would like just to modulate a sine wave by a ...
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1answer
25 views
Extracting different frequency bands (alpha, beta, gamma) from MEG source estimated data
I have a dataset that consists of source estimated data of MEG brain signals.
I need to extract the different frequency band features (i.e., alpha, beta, gamma, etc) from them.
What steps/procedure ...
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1answer
43 views
DSP: newbie not understanding z transform/complex sinusoidal frequency and phase
Im reading Will Pirkles Designing audio effect plugins book and I'm not sure if I'm understanding the z transform correctly. I got up to differential equations in college, but haven't done math in ...
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1answer
22 views
What should be my sampling frequency for a peak detector output where it is extremely important for me to capture the first time the peak occured?
Following is the output of the peak detector:
The amplitude is not important to me, however the time when the peak occurs is extremely important. So my microcontroller will have an algorithm like ...
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2answers
52 views
Nyquist Frequency and Window Length
The Nyquist theorem states that the sampling rate must be twice the highest frequency to be observed. How does the length of the interval play into this relationship?
The main resource that I found ...
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1answer
132 views
Aliasing below $f_s/2$
phi = exp(linspace(0, log(511), 1024)) - 1
x = cos(2 * pi * phi)
Above will alias, despite peak instantaneous frequency evaluating to ...
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1answer
37 views
Fine frequency correction : grouping and finding max amplitude inside a group
I work on phase and frequency estimation algorithm. Currently I am working on a derivation and determination of the Doppler shift( dF – frequency step).
For each dF, The following algorithm was ...
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1answer
44 views
How do I determine the carrier frequency of a given AM signal?
I am trying to figure out what the carrier frequency of a signal is given only its discrete-time domain information and the fact that it is a signal on the AM radio frequency band(550 - 1700kHz). Is ...
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1answer
65 views
How to calculate PSD if i have power vs freq spectrum?
i have a signal something like this
how to calculate PSD?
i have freq from 191000200 to 196500000
time gap or delta t = 1 or 2 sec, (what i mean is [tn] - [tn-1])
i will be computing in python any ...
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1answer
49 views
Karplus-Strong with Jaffe-Smith sample rate-independent
I tried to implement the Karplus-Strong algorithm with some of the Jaffe-Smith extensions (improve pitch, dynamics, etc). Here is the code.
When I run it with a sampleRate of 48000Hz, I get very ...
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1answer
34 views
Extraction of the phase lag form cross-correlation function
I would like to find out the phase offset that my signal contains at the receiver side. For this, I use the cross-correlation function, where I cross-correlate signal before and after matched filter. ...
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1answer
66 views
How does one interpret an element of the “transfer matrix” used to calculate frequency domain granger causality (via VAR models)?
I am attempting to gain a better mathematical understanding for how autoregressive models can be used to infer frequency-domain granger causality. All freq. domain measures of causality that utilize ...
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1answer
49 views
How to calculate the instantaneous frequency for one specfic signal?
I have a signal which like this:
I want to calculate this signal's instantaneous frequency.I have tried hht and so on which method I can find but can not get the result.
So does somebody can give me ...
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2answers
589 views
Amplitude modulation vs sampling rate?
As a sampled tone's frequency nears $f_s / 2$, amplitude modulation grows apparent:
("Actual" curve in grey; blue is what we get if taking samples (dots) "at face value"). This is ...
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1answer
54 views
Bandpass filter equivalent for amplitude
I have a signal where I am using a bandpass filter to limit the frequency range. I am also interested in filtering the remaining frequencies (after bandpass filtering) within the signal by their ...
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1answer
31 views
Belt tension measurement (36 Hz): What should my FFT size be? [closed]
These are my setting that I can adjust and I need to measure 36 Hz. +- 1 Hz.
What settings do you recommend?
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1answer
24 views
Transmitting an approximate CW with an FM modulator
Imagine we had an FM modulator with carrier frecuency $f_c$. My doubt is about the optimal approach to use it for transmitting a tone (CW) of a frequency $f_c+\Delta f$.
Let $x(t)$ a and $y(t)$ be the ...
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1answer
38 views
Amplitude decrease in FFT at higher frequency for multisine
I am adding sine signals with different frequencies but same amplitude=100.
Sampling frequency is 50MHz.
I am not getting 100 in frequency domain for frequency 787KHz.
At 1K, 3K I am getting 100 ...
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0answers
23 views
Breaking EEG signal into epochs: why should we multipy windows-time length by frequency?
I am new to EEG data, Could you please explain why we need to multiply Fs by window_time_length ? I thought by defining window_time_length, we define the length of epoch!
I am working on P300 BCI ...
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67 views
Transfer of the signal spectrum to zero frequency
There is a signal at a frequency of 6 kHz-6.5 kHz. Sample rate 40kHz. It is required to transfer it to zero frequency.
I counted two arrays cos and sin:
...
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60 views
DTFT and Eigenvalues in frequency domain
Consider an LTI system with impulse response $h[k]$. Does the frequency response $H(e^{j\Omega})$ equal the eigenvalue corresponding to an eigensignal of frequency $\Omega$?
So if I convolve an ...
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1answer
40 views
Optimal sampling frequency
I am working with microcontroller's ADC to sample the data. I know that Nyquist criteria tells us that the sampling frequency should be at least twice the highest frequency, but it might involve ...
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5answers
206 views
instantaneous frequency for a sum
In the literature, the instantaneous frequency for a signal $s(t)=e^{-j \phi(t)}$ is given by: $$f(t)=\tfrac{1}{2\pi}\frac{d\phi(t)}{dt}$$
This my problem: I have a signal $$u(t)=e^{-j \alpha_1 \phi(...
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1answer
41 views
Spectrum in real life with Spectrum in theory
as you know it is possible to measure the power spectral density ($|X(f)|^2$) of a certain voltage signal $x(t)$ through a Spectrum Analyzer.
As far as I'm concerned, the simplest spectrum analyzer ...
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1answer
75 views
Why is GPS 1575 MHz?
I’ve read that that frequency is a ‘window’ in weather, impacted less by raindrops for example. I otherwise would’ve thought that simply increasing the wavelength would decrease impact. I don’t ...
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1answer
93 views
SMA, SVM and PSD python
I'm looking for python functions (package) to calculate SMA (signal magnitude area), SVM (signal vector magnitude) and PSD (Power Spectral Density). The goal is to extract features from an ...
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Estimating Average HR from PPG sensor
I am reading Smartphone based Blood Pressure Monitoring via the Oscillometric Finger Pressing Method, which is trying to estimate blood pressure from a PPG sensor and a small applied force finger ...
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1answer
82 views
Generating a time domain signal using the fundamental frequencies
I currently have the power spectrum (in dB) of a signal through which I obtained the fundamental frequencies and amplitudes. My question is: how to generate a time domain signal using these amplitudes ...
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28 views
RRC filter in receiver side well applied?
I would like to ask question bout the rrc filter that I applied as an matched filter for receiver side in communication. My aim after RRC filter is to draw the eye diagram, and so far the eye opening ...
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40 views
The timing offset remains after Gardner loop
I would like to use Gardner loop to remove the timing offset in order to demodulate the signal. My signal contains the frequency offset, however I know that the Gardner loop can handle substantial ...
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2answers
60 views
Understanding FFT for a vibrational analysis experiment
I am trying to understand how FFT works in order to measure the vibrations of a 3D printer. I will be doing this with an Arduino Nano and a MPU6050 accelerometer.
In order to program the Arduino ...
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1answer
77 views
How to take into account phase differences when doing Fourier Transform?
I apologize if the title seems very vague, I don't really know how to put it a different way.
From what I understand, the Fourier transform is essentially just doing a dot product between multiple ...
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1answer
104 views
Symbol timing recovery in Python
My objective is to demodulate QPSK signal. At the receiver I apply RRC filter and interpolate the signal to get the values of the signal (approximately) at the sampling instances. Then I am concerned ...
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3answers
332 views
Difference between OFDM and FDM
In Frequency Division Multiplexing we provide one channel to one user.
Example like BandWidth of user1's voice is 200Khz. I provide one channel of 200KHz in FDM for uplink as shown in the figure.
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1answer
125 views
Why does this transfer function estimation not work? System identification
Goal:
I have an unknow dynmical system $G(s)$ and I want to find it from measurement data, output $y(t)$ and input $u(t)$. The data is frequency responses.
Method:
I begun first with creating the ...
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3answers
256 views
Downsampling vs. ADC with lower Sample-Rate
I would like to know in general where the advantages and disadvantages are:
Downsampling of a high sampled continuous analog signal in FPGA or µC and
Direct use of a lower sampling rate, i.e. using ...
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0answers
8 views
Matlab function rpmfreqmap doesn't show diagonal lines though there is variation in speed
Matlab function rpmfreqmap doesn't show diagonal lines though there is variation in speed. I'm using vibration and tachometer data from dataset. I'm trying to perform order analysis as shown in Matlab ...
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1answer
54 views
What does frequency weighting an acceleration signal mean? And How do I frequency weight the raw acceleration data collected?
Disclaimer: I have very little knowledge in signal processing.
I'm trying to calculate a Whole Body Vibration(WBV) measure called Vibration Dose value(VDV).
$$VDV = \left(\int_{0}^{T}a(t)^4\,dt\right)^...
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1answer
45 views
How to obtain the exact value of wavelength from a 2D FFT amplitude vs wavenumber plot like it is obtainable from 1D FFT amplitude vs wavenumber plot?
I have a two dimensional multi modal spatial signal generated from a MATLAB code using sinusoidal functions of different wave numbers, amplitudes and phases. What I want to know is that if I have the ...
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1answer
94 views
QPSK demodulation
My objective is to demodulate QPSK signal. At this moment, my constellation in the best case looks like in the picture below:
and the corresponding eye-pattern:
Eyes are completely closed, which ...
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17 views
What is the use of quasi logarithmic frequency distribution in multisine frequency signal in finding FFT
I'm using multisine but recommended to use quasi log frequency distribution to find out FFT.
What is the advantage of using this?
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2answers
55 views
Frequency slows faster when it's decreasing
I'm sure there's a simple explanation but I can't discover it. Consider two frequencies, a and b. a is higher than b. I can create a wave with both frequencies. But when I create a wave with frequency ...
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2answers
6k views
Equidistant log scale points
I have an x-axis which is in logarithmic scale representing frequency, I would like to have NumPoints on this axis that are equidistant on the log scale, I have the following variables:
Fmin = 100
...
