Questions tagged [frequency]
Frequency in signal processing is the number of cycles (of the signal) per second.
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What is the physical significance of negative frequencies?
This has been one of the holes in my cheddar cheese block of understanding DSP, so what is the physical interpretation of having a negative frequency?
If you have a physical tone at some frequency ...
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4answers
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What is meant by a system's “impulse response” and “frequency response?”
Can anyone state the difference between frequency response and impulse response in simple English?
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Which time-frequency coefficients does the Wavelet transform compute?
The Fast Fourier Transform takes $\mathcal O(N \log N)$ operations, while the Fast Wavelet Transform takes $\mathcal O(N)$. But what, specifically, does the FWT compute?
Although they are often ...
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2answers
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FFT frequency resolution
I'm having some problems understanding the FFT. Is the frequency resolution in the spectrum calculated as
$\frac{\textrm{sampling rate}}{\textrm{number of FFT points}}$ or $\frac{\textrm{sampling ...
34
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9answers
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Is there an algorithm for finding a frequency without DFT or FFT?
I was looking in the Android app store for a guitar tuner. I found a tuner app that claimed it was faster than other apps. It claimed it could find the frequency without using the DFT (I wish I still ...
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2answers
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Image Reconstruction:Phase vs. Magnitude
Figure 1.(c) shows the Test image reconstructed from MAGNITUDE spectrum only. We can say that the intensity values of LOW frequency pixels are comparatively more than HIGH frequency pixels.
Figure 1.(...
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Detecting drum bpm in a noisy .wav file
I am looking for algorithm(s) to solve the following problem:
Given a noisy .wav sound capture (some wind + friction noise on the microphone), how to detect the BPM of a soft drum beat?
I have ...
7
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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 ...
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3answers
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FFT for a specific frequency range.
I would like to convert a signal to frequency domain. The desired frequency range is 0.1 Hz to 1 Hz and the frequency resolution ...
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2answers
1k views
Frequency Analysis of a Signal Without a Constant Sampling Frequency (Non Uniform Sampling in Time Domain)
I'm a stack exchange user for some time and now I'm registering to ask a simple question (I think!).
I have a vibration signal with an amplitude and time (sampling frequency not constant) in a $...
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4answers
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Discrete Time Signal Property
Property:
The frequency of oscillation of discrete time sinusoids sequence increases as $\omega$ increases from $0$ to $\pi$. If $\omega$ is increased from $\pi$ to $2\pi$ then frequency of ...
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4answers
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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, ...
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1answer
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Determine fundamental period from zero crossing signal
I have got a signal which consists of zero crossings over discrete time and I would like to estimate the fundamental frequency (period) from this signal in order to remove noisy samples.
The signal ...
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2answers
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Signal Processing/FFT gives very high magnitudes for low frequencies
The script essentially pulls PCM data from the sound card and stores them in a buffer. Then I apply fft and graph it. I am looking through this blog post for some examples and ideas on how to ...
2
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1answer
169 views
Magnitude value of filter frequency response
Can someone help me with this problem:
Suppose we filter signals with the below pre-emphasis filter:
$$y[n]=x[n]-0.8x[n-1]$$
I have to calculate the impulse response of the filter (ok easy) and ...
0
votes
1answer
380 views
Average FFT Magnitude in bins
I am analyzing sounds of daily activities recorded by a smartphone. For example walking, getting up from bed, falling, running etc.. (one at the time).
Let’s take one them. My goal is to
convert from ...
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3answers
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what is the gabor filter, and what are its main uses
I'm doing a research on Gabor filter, but when I Googled it, I had very long and complicated articles. Can anyone help me to find a simple explanation about it, or recommend a website or article to ...
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2answers
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How do I determine if a discrete signal is periodic or not?
I want to know how I can determine whether a series of data is periodic or not.
I want to use Fourier transform/series. My data looks either aperiodic
[111100001111000110010101010000101]
or ...
14
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3answers
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How can I plot frequency vs magnitude of wavelet transform?
I am running Morlet continuous wavelet transform. I have got wscalogram of signal and now I want to plot freq-magnitude like the following picture., but I don't ...
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1answer
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Why should one use windowing functions for FFT?
So I just revised my pitch calculation algorithm using a harmonic product spectrum algorithm. I was just curious about why this explanation of Harmonic Product Spectrum states that you need to ...
11
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3answers
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What is the bandwidth of a (real) sinusoidal tone, and pulse?
I would like to know how to go about calculating the bandwidth of:
A constant (real) sinusoidal tone
A (real) sinusoidal pulse.
The question is as simple as that, but I am having a hard time with ...
6
votes
2answers
3k views
Setup frequency array properly
I've just stepped into the FFT's world since the last weeks, therefore I still don't have an clear overall idea of how to setup the frequency array.
In case of even...
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2answers
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Amplitude of the Signal in Frequency Domain different from Time Domain
How does the Amplitude of the Signal is changed when taking the FFT of a Signal,
Have a look,
The amplitude had changed from 2 to 30,
and Here is my code for generating the above output,
...
3
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2answers
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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 ...
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2answers
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How is it possible to Filter out a person's voice out of 100 of other voices?
So, I've just learned that the human voice is not a single sine wave its a bunch of unlimited Sine waves each having a different frequencies,
According to Wikipedia,
The voice consists of sound ...
5
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1answer
323 views
Understanding the $\mathcal Z$-transform
I was studying $\mathcal Z$-transforms and found pretty good material on the topic, though I feel I do not have a proper understanding of the concept. Could someone help me clarify this?
I know that ...
4
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1answer
3k views
Why is oversampling helpful to an anti-alias filter?
Why does oversampling make the job of an anti-alias filter easier? I don't understand the intuition on why it becomes helpful.
Isn't it economical to just keep the sampling rate at the minimal level,...
3
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3answers
3k views
How to compute fundamental frequency from a list of overtones?
Given a list of overtones (F1, F2, F3, etc), how do I compute the fundamental frequency? Can I do something like F2/F1=F1/F0? Is it the correct method to use?
2
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2answers
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Frequency vector and fft
I have got a question concerning the definition of the frequency vector for an fft operation.
Generally, I work with a frequency vector, f, with power of 2 ...
2
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1answer
2k views
Performing classification based on FFT results
It is perhaps important to start with the fact that I am a complete beginner in DSP.
I have got a number of audio recordings (of sampling rate 22 kHz) - of bird songs - which I have been trying to ...
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0answers
743 views
How can I identify the damping of the modes in a signal by Cmor wavelet method?
I read several papers which proposed a method to identify modal parameters. such as natural frequency and damping ratio.I've tried to implement those methods by Matlab.but I couldn't get the result.It ...
6
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1answer
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Why can Quadrature Demodulation demod a Frequency Modulated Signal?
I use a Quadrature Demodulator in my SDR application, which is defined as:
$\angle (S_n, S_{n+1})=arctan(S_{n+1}*\overline{S_{n}})$
So practically its amplitude is the angle between two Samples $S_n$...
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3answers
730 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 ...
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3answers
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What's the best criterion for determining a frequency peak?
I'm writing an algorithm that analyzes results of discrete Fourier transform (DFT). The algorithm should detect amplitude peaks in predefined ranges of frequencies. This is an example of such a peak:
...
3
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3answers
281 views
Determining the period of a discontinuous function
I'm new to the field of DSP.
I'm trying to determine the period and shift of the function. I've tried using FFT, but haven't had much luck. Seems like it should be simple.
Signal (pastebin of ...
2
votes
1answer
727 views
What features describe audio signals? (Besides frequency and amplitude)
I recorded sounds with a microphone and I try to distinguish them in my Java program. The frequency works quite good, but if I look at the fourier transforms it seems like there should be more ...
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2answers
171 views
Generating a sound where end frequency is 1/2 of the start frequency
I am very very new to signals, and I am trying to generate sounds based on some parameters from a database. So, the database stores the following:
startFrequency
endFrequency
startAmplitude
...
2
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1answer
3k views
Remove a frequency and all its multiple (harmonics)
In a soundfile, I'd like to remove a frequency and all its harmonics. What is the best solution in your opinion ?
Do a loop with 20 notch filters, one after another.
// f is the fundamental ...
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3answers
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FFT bin interpolation for low frequency with DC offset
I have a noisy signal in I/Q format with a peak frequency that constantly changes between 0.5Hz and 4Hz. The sample rate is 64Hz. I want an output showing the current peak frequency with a maximum lag ...
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3answers
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Fundamental frequency
Can someone help me:
I have a signal which consist of three frequencies; for example, $f_1=800\,\text{Hz}$, $f_2=1050\,\text{Hz}$, $f_3=1600\,\text{Hz}$. How can i compute the fundamental frequency?
...
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1answer
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Doppler shift in time domain?
I have some clarifications required in this topic
So initially I know that to shift a signal $X(f)$ by $f_0$ we need to take its inverse fourier transform and multiply it with a factor of $\exp(−j2\pi ...
5
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4answers
421 views
How to find period/envelope that is larger than sample size?
Mercury's distance from the solar system's barycenter (in kilometers)
can be approximated as:
...
4
votes
2answers
756 views
Separating waves of very close wavelengths
I'm new to wave problems, so excuse my simplified words.
I have a signal consists of high range of frequencies . I applied a Band-pass filter to this signal and I have been able to separate it to ...
4
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1answer
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Upsample data using FFTs. How is this exactly done?
I am basing my question on this post here, because I would like additional details on it, as I have not had any success in re-creating it.
I would like to simply learn, in no uncertain terms, how to ...
3
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2answers
537 views
Comb-like peaks in frequency spectrum
I am currently working on a project which involves measuring the sound produced by the onset of a vapour bubble in boiling water. All the experiments went perfectly well and I'm now trying to obtain a ...
3
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2answers
9k views
FFT for a single frequency
I was looking for a more efficient way of finding the magnitude and phase of a signal at a certain frequency without performing an FFT because it produces more information than I need and I came ...
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3answers
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FFT Zero Padding - Amplitude Change
I'm just learning about Fourier Transforms and as an input I'm using a WAV file (Matlab) and taking one channel of it and performing a quick Fourier transform. I've zero padded the input, as I've been ...
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1answer
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Sampling frequency of modulated signal
A very naive question... A signal with bandwidth of 20 MHz is modulated using a carrier of 1 GHz. What will be the sampling frequency?
I was asked this question during an interview. I answered 2 GHz ...
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4answers
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Very basic question about how we define frequency in signal processing
When talking about general periodic continuous-time signals for which $$x(t + T_0) = x(t)$$ where $T_0$ is the fundamental period we define the fundamental frequency $\omega_0$ as $\omega_0 = 2\pi/T_0$...
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1answer
401 views
Sampling bandpass signal with spectral replications
I want to clear my thinking on how to approach problems of the type characterized below.
I guess what we want to do is select a sample rate of a sufficient size such that this signal can be fully ...
