Questions tagged [frequency]
Frequency in signal processing is the number of cycles (of the signal) per second.
486
questions
4
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3answers
18k views
Calculating values of frequency bins in Python
I have to use FFT to determine the period of waves inside a signal. After applying FFT on a window of 10000 point from a signal, I get something like this:
What I don't understand is that FFT is ...
0
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0answers
27 views
How do I find the peak frequency of a wav file in python?
I am fairly new to python and signal processing and I was given a task to record audio for 'x' seconds and then find the peak frequency in the audio file.
So far I have successfully implemented the ...
0
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1answer
38 views
DFT and integer valued basis functions'sf requencies
In Matlab the function
W=dftmtx(N)
gives the DFT matrix of size N.
Each row is computed for an integer frequency k. $W_{k,n} = e^{-i2\pi kn/N}$, k-th frequency, ...
0
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2answers
7k views
How to calculate the frequency of a signal without knowing the sampling frequency using Matlab
I have a signal and I am using Matlab command pwelch to calculate the frequency of the signal, but the frequency I obtained is changed as I change the sampling frequency.
For example, when using ...
1
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1answer
45 views
STFT output frequency does not match sin wave frequency
I have the following function and pre definition for producing a sin and its' stft:
...
0
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0answers
33 views
Correlation between frequency and initial phase estimates using FFT
Why is there a high negative correlation between frequency estimation errors and initial phase estimation errors when measured using FFT?
I have a simple code showing this negative correlation.
is ...
1
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0answers
41 views
Aliased Signal's Frequency
So I have an incoming signal of 137.9 MHz and a sampling frequency of 1.4 MHz. Once sampled how do I calculate the aliased ...
0
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1answer
25 views
Power and Energy of an Audio file
I have a question about calculating the power and Energy of an audio recording.
I have imported a waveform of an audio recording in WAV format into Matlab and then calculated the energy and power in ...
0
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1answer
5k views
How to change a continuous signal to form a discrete signal? [closed]
I have a continuous signal $$ x(t)= 2\cos(200\pi t)+8\cos(250\pi t)$$ and it is sampled at 400Hz.
How is this changed into the discrete time domain in order to determine the two discrete frequency ...
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1answer
23 views
Digital carrier recovery
I was reading Chapter 2 from "Telecommunication Breakdown" by Johnson and Sethares and came across this paragraph:
However, sometimes it is more cost effective to perform certain tasks
in analog ...
2
votes
1answer
63 views
Is there a good method to extract a reference sin/cos from a group of signals?
For the removal of a pure interference from a group of sampled signals, if I know the exact frequency of the interference I can simply use an I/Q demodulation technique (i.e., a phasor projection) to ...
0
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0answers
80 views
Butterworth cutoff frequency normalization
The issue: I am trying to reproduce the step detection technique as described in this paper. You can see the proposed step detection in the image below. The first part of this technique is to use a ...
1
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2answers
680 views
Impact of modulation index in FM
If I have the spectrum of a FM modulation, does the frequency of the carrier disappear when the modulation index is too big?
Does the amplitude of any side band depend from the modulation index?
And ...
0
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0answers
46 views
How to find frequency and corresponding time for an audio signal?
I want to read in a sound file and get the frequency at each time interval of the signal.
I thought that the best way to approach this is by applying FFT to small chunks of the signal. Because FFT ...
0
votes
1answer
119 views
Mel separated filter banks
I am currently a bit confused.
I am currently trying to understand the MFCC extraction process, and don't understand how the Mel filter banks only provide a scalar output from each filter bank. What ...
1
vote
1answer
39 views
Calculate aliasing of $x_a(t) = \cos{(2\pi300t)} + \cos(2\pi600t)$ when sampled with $F_s = 1000$
I'm asked to sample the signal
$$x_a(t) = \cos{(2\pi300t)} + \cos(2\pi600t)$$
with sampling frequency $F_s = 1000$ and plot the magnitude spectrum for the resulting sampled signal.
My thinking is ...
3
votes
2answers
165 views
Lock-in amplifier
From what I have studied so far I have understood that the benefit of a lock in amp is its ability to resolve the amplitude of a signal which is deep into noise.
I was wondering if the same concept ...
-2
votes
1answer
90 views
What does a fractional frequency (for discrete-time signals) mean/how to interpret it? [closed]
This question has bugged me for a while as it's not addressed in any books I've read. I was wondering how folks from this community interpreted it. Below are my personal notes on the matter (please ...
0
votes
3answers
613 views
Distribution of energy in frequency bands
On my wav-file (music), I do a short-time Fourier transform (STFT). I have spectrum, which spans from $0\textrm{ Hz}$ to $f_s/2$. I took out the range between $1$ and $1000\textrm{ Hz}$, which I ...
1
vote
1answer
130 views
How can I get the power of a specific frequency band after FFT?
I need help with my matlab code. I have recorded EEG data and now I want to analyse it in matlab. I want to find the mean power of specific frequency ranges (theta: 4-8 Hz,alpha: 8-12Hz etc.). For ...
0
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1answer
181 views
Wavelet central frequency
What is the definition of the central frequency of a Wavelet and the bandwidth of a Wavelet? How do they affect the resultant waveform of the wavelet?
Thanks.
0
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1answer
440 views
When listening in to an AM signals of various frequencies, how do we exactly tune in?
Alright, so I read on AM and Double Sideband AM, but I don't the more fundamental idea - the frequencies.
Frequency is just: $ \frac{1}{T} $, where T is period
So difference between 5 Hz and 30 Hz ...
1
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1answer
61 views
Break a signal into segments, add them together and then perform an FFT on the result
If you break a 4 second signal into 0.5 second segments, add them together and then perform an FFT on the resultant 0.5 second data.
Will the FFT / frequency spectrum be the simlar to an FFT on the ...
2
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0answers
19 views
Is it possible to create a causal filter with a positively-sloped phase response?
I am currently prototyping a set of noise-cancelling headphones that utilize active EQ to modify the noise-cancelling signal, allowing the user to modify the frequencies that they hear or don't hear. ...
0
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0answers
34 views
Practical Signal Processing by Mark Owen Exercise 2.1. and 2.2
The following exercises don't have answers in Practical Signal Processing by Mark Owen. What is the author looking for here? A mathematical proof?
2.1 A cosine wave of frequency f is sampled at $t = ...
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0answers
9 views
Complex Spectral Phase Evolution (CSPE) Performance depending on signal windowing?
I am look into CSPE. "Signal Analysis Using the Complex Spectral Phase Evolution (CSPE) Method"
The method is simple. It compares the original signal's FFT and shifted signal FFT in phase domain so ...
1
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4answers
197 views
How to see the amplitude of each frequency?
do you know software that exports spectrograms to images of 500x22000 pixels?
all the spectrograms that I know show diffused frequencies and it does not look very good
I just want to see the amplitude ...
2
votes
2answers
216 views
Do Fourier frequencies actually exist in real life in form of “fundamental frequency”?
For me, this is a very awkward question to be asked, as at this point in my studies I'm supposed to be quite expert with elementary mathematical tools like Fourier transforms, but this has always ...
0
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1answer
73 views
Formant Analysis Frequency - What makes a peak value?
from spectrograms, how can you tell which peak is really a formant. Like why is the pink arrow the first formant. And in the spectrogram below, which has fewer samples, what makes a value the peak ...
1
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1answer
70 views
Term for integral multiples of fundamental period?
As we know that a signal has fundamental frequency and integral multiples of fundamental frequency are known as harmonics
I am curious about the term that will be used for integral multiples of ...
0
votes
0answers
14 views
Interpreting results of multiplying signal and wavelets in the frequency domain
I have followed a lot of stuff on mike cohens website and have managed to make a filterbank of Morlet wavelets and convolve with an incoming block of samples. This of course is a computationally heave ...
1
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1answer
2k views
How to Normalize Frequency in MATLAB
I know all about conversion of frequency from HZ to normalized frequency and from normalized frequency to angular frequency ,but I wonder how it is done in MATLAB.
I have the following code:
...
2
votes
4answers
14k views
Designing High Pass Filter to Remove DC Offset from a Signal
I want to design a high pass filter (f0*S/1+f0*S) in order to remove the dc offset from a signal ? (i.e. how to choose the frequency f0).
Thanks,
Hacene
Ps : the filter is for MATLAB implementation, ...
0
votes
2answers
241 views
In case of using a Doppler radar, do we have to use IQ demodulation to find the direction of a target?
I want to know the way to find the velocity of a target by using a doppler radar.
I read some paper about it,
In summary,
send rf signal to a target
receive the reflected signal from the target.
...
0
votes
1answer
54 views
How do I find the frequency of a particular bin in a cosine transform, and two other questions
I have a discrete series of values and I have applied a Discrete Cosine Transform to it, obtaining values like:
...
1
vote
1answer
128 views
Chebyshev I or Chebyshev II?
I am new to DSP, and I am trying to recreate some analysis of a signal,
They use a chebyshev I filter to go from a 100Hz signal to a 50Hz signal. Whereas I am currently using a chebyshev II filter, ...
0
votes
0answers
33 views
histogram bin size vs. data sampling rate
I have a set of numerical signals that give me a set of zeros calculated based on some numerical procedure. I make a histogram of those zeros.
Here, a following problem arises:
If the histogram ...
0
votes
2answers
105 views
May I know how to find Time frequency power spectrogram of a signal?
I am analyzing EEG signal and I am unable to understand the term Time-Frequency Power Spectrogram. Please Can anyone help me?
Thank you in advance.
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2answers
500 views
Nyquist frequency and DC
Im studying the DSP book by Steven W. Smith. On page 41 he covers the Nyquist frequency. He makes up an example by writing the following.
... consider an analog signal composed of frequencies ...
-1
votes
4answers
480 views
What are real-valued and complex signals and why is the Fourier transform of a real-valued signal Hermitian?
I have confusions in these concepts:
What are real-valued signals?
What is the difference between it and complex signals?
Why is it so that for real-valued signals, the spectrum of negative ...
1
vote
1answer
85 views
How is frequency related to data rate?
How does (if it does) frequency affect/relates to Data Rate.
Why for example using the same modulation, LoRa (in the physical layer),
you get somewhere around 250kbps at 2.4Ghz and only 20kbps at ...
0
votes
0answers
32 views
Temporally locating beats in an audio file
Imagine you have a long recording of a guitar player playing an arpeggio at a slow speed. To simplify, assume the tempo is 60 bpm or lower. I want to annotate this recording with the exact moments ...
0
votes
0answers
9 views
user multiplexing in NOMA system
when two users are multiplexed in downlink noma system using the same subcarrier i,the throughput can be expressed as
How to form the throughput expression in downlink noma system when two users ...
0
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0answers
22 views
Downlink NOMA system
In what manner does subcarrier,frequency,channel are related in downlink NOMA.
How does the subcarrier allocation takes place when users are getting grouped into clusters on the same frequency....
0
votes
2answers
205 views
How to increase resolution of FFT?
I have an input signal in the ( 0 - 20 kHz ) frequency range . When i sample this signal maximum sampling frequency is around 40 kHz . When i calculate the FFT using 1024 points i got resolution of ...
1
vote
1answer
225 views
What is the relationship between angular frequency and normalized angular frequency
This is a slide from my lecture notes:
My professor used the following words " We denote digital frequencies with capital letters and analogue frequencies with lower case letters"
The problem I have ...
0
votes
2answers
196 views
Noise power and bandwidth
$$N=kTB$$
In this formula for calculating noise power, why do we use the total bandwidth of the system?
I mean our signal is at $f_0$ carrier frequency, why is it effected by a large bandwidth and ...
0
votes
1answer
26 views
Frequency spectra of a sampled process
I have a process $X$ with frequency spectra
I sample this process with sampling frequency $f_s = 2$.
What will the frequency spectra $R_z(f)$ of the sampled process $Z$ look like? I realize that ...
3
votes
3answers
5k views
How to correctly compute the EEG Frequency Bands with Python?
so I am trying to compute the EEG(25 channels, 512 sampling rate, 248832/channel) bands (alpha, beta, gamma, etc.) with Python. I managed to do so by: firstly filtering the signal with a butterworth ...
7
votes
1answer
1k views
Why does a wave continuously decreasing in frequency start increasing its frequency past the half of its length?
I'm trying to programmatically generate a wave (sine or square) with a continuously decreasing frequency.
To do so, I simply multiply the starting frequency for a decreasing value, that linearly goes ...
