# Questions tagged [frequency-spectrum]

The frequency spectrum of a time-domain signal is a representation of that signal in the frequency domain.

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### Which FFT Window to use for data gathering of complete mastered songs - for AI

I have a novel technology that I developed, which I plan on incorporating AI beginning with simply recording a basic machine learning strategy of Input - Output for eventual training. In this case ...
662 views

### For the square wave signal, why does a narrower square wave correspond to more spread in the frequency domain?

Consider the square wave. As we decrease the pulse width $T_1$, it seems that the positive Fourier coefficients (located in the central area/lobe) are spreaded out across more frequencies. In fact, if ...
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### Identification of the spectrum color of a coded video signal

I have two encoded video signals (MPEG and H.263). In each file, I have information about the frames of the video. I calculated the autocorrelation and then did the Fourier transform to find and plot ...
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### Phase noise influence on ADC in bistatic FMCW Radar

I am currently studying the topic of oscillator phase noise in frequency modulated continuous wave (FMCW) radar. In my specific case, the radar is implemented on an FPGA (AMD RFSoC). Thus, the echo is ...
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1 vote
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### ML-Classification of Motor Imagery EEG data only at 50% in MatLab

I'm trying to do ML-classification on some Motor Imagery EEG data and for a long time now I've been stuck at ~50% being correctly classified. This is my first time working with EEG data and signal-...
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### What is the relationship between sound frequency that generated by fan and the RPM of fan itself?

So I just bought high RPM external fan for laptop. It doesn't have sensor. So it's purely actuator device. Therefore the cheap measurement I can do, is using my phone microphone and open spectrogram ...
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### Comparing Spectral Leakage in Sine and Cosine Functions

I am not from a signal processing background, kindly excuse me for my vocabulary. When I compute the power spectrum of a periodic function, where the "real" space variables are generated by <...
1 vote
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### Baseband downconversion without imaging

I am a high school intern at a company employing heavy DSP and trying to learn the basics from the ground up. One feature of a test application I'm creating is the ability to zoom an FFT graph and ...
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### very basic confusion about the bandwidth of constant signal function

I have a very basic question about bandwidth of constant function $f(t) = K$. As the Fourier transform of a constant pulse is a delta-function centered at zero frequency, the bandwidth (maximum value ...
1 vote
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### How to measure the vibration of an object on a video shot at high speed camera?

I have a video fragment which I split into frames (pictures). I use them in pairs (1 frame with 2, 2 with 3, etc.) to find shifts on x and y axes (i.e. how much I need to shift 1 frame to make it like ...
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### Getting the magnitude and phase of a single specific frequency from an audio signal

Assuming I only care to calculate the magnitude and phase of ONE single frequency from a signal, how can I get this information without calculating anything else? For example I want to come up with an ...
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### Constant Q transform where you keep the window size constant (so Q is no longer constant)?

I've been working on implementing a constant Q transform to try and detect musical notes within an audio signal and I came across an issue. When trying to detect low frequencies the constant Q ...
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### How can I use a constant Q transform to detect low frequencies without making the buffer size too large?

I am trying to write code to detect musical notes within a signal. I have been reading up on different methods for extracting frequency information out of a signal to determine which notes were played ...
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66 views

### Why the Discrete time fourier series coefficients of a real discrete time periodic signal are not symmetric about y axis?

If the signal is something like cos(πn/3) , we get the two DTFS coefficients that are symmetric about y axis and the resulting frequency spectrum is an even function . Now take the example given in ...
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### How to compute the 2D coordinate in the s-domain?

I am not sure if my question is a right question to ask or not since I am still learning about Laplace Transform and S-Domain. If we have 2D coordinates (x,y) in the spatial domain (i.e., Euclidean ...
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### Is the magnitude spectrum of the Discrete Time Fourier Series of a Discrete Time periodic Signal , an even Function?

We know that the magnitude spectrum of a continuous time fourier series representation of a real periodic signal is an even function (i.e. symmetric about y axis). Does this hold true for discrete ...
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### Comparing custom Welch periodogram with Julia's Welch periodogram

I wrote my own PSD struct in Julia for practice purposes. It involves two type of constructors: a "direct" PSD and a <...
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158 views

### Effects of Hanning window on power

I have written this function in R to compute the power spectrum density (PSD) of a signal: ...
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### How signal generation affect its spectrum

Im trying to get dft of hanning window. Im trying different methods of generating the same signal, yet im resulting with such different graph of signal spectrum. ...
1 vote
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### Trying to replicate results from tfestimate function in Matlab

I have been trying to replicate the results from the tfestimate function in Matlab by performing, from my understanding, the corresponding signal processing steps in a separate Matlab script file. The ...
49 views

### Looking for an online course

I work for a company with expertise in electromagnetics physics, specifically dealing with time domain-based simulation software. We routinely need to transform our results into frequency domain, ...
70 views

### What function can be used to describe periodicity of the signal

im working on a program in matlab for calculation of sampled signal spectrum, and I have a sinusoidal signal with frequency f=100 Hz, sampling frequency fs=250 Hz, every sample is repeated 4 times (fr=...
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### computing the averge power spectral density with python

In order to compute the power spectral density of a signal, we can use np.fft.ftt in python in the following formula: ...
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### Result of complex exponential fourier series approximation and trignometric fourier series approximation are not exactly same in MATLAB?

I have a signal and i am trying to observe its approximations using complex exponential fourier series and trignometric fourier series but i am not getting exactly same result(graph of trignometirc ...
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1 vote
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### How can it be possible that I hear people voice from my computer speaker?

I searched on web and apparently can be due to truck drivers communicating at CB band which is around 20MHz. And apparently this communication may interference with the frequencies used by computer's ...
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### DFT Matrix Oversampled In Frequency?

Edit 2: I am trying to replicate results from this paper Compressed Sensing with Coherent and Redundant Dictionaries. On page 3 the "oversampled DFT" is mentioned as an example of an "...
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### Since harmonics only generate at multiples of the center freq, is it for this reason that the left part of a FT (like sinc) has no physical meaning?

If we have a rectangular pulse function, we know that after a Fourier transform we obtain a sinc: We know that the left part (negative frequencies) has no physical meaning and it's just specular. It'...
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### In the frequency domain of a phase-shift keyed signal, why there are are prominent frequency components which are multiples of sampling frequency?

In the frequency domain representation of a digital phase modulated signal, why there are prominent other frequency components which are multiples of the sampling frequency, other than the main ...
1 vote
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### Is there something wrong with MATLAB's pwelch function?

The normalized factor for windowing, is it $(\sum w[n])^2$ or $\sum w^2[n]$? I try to reproduce the pwelch function, if I set the normalized factor to $(\sum w[n])^2$, I get the same result as MATLAB ...
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### Bandwidth of a complex pole

Text from "Fundamentals of Speech Recognition (Rabiner)". A complex pole of the LPC model spectrum can be expressed as $Z_i = > r_i \cdot e^{j \omega_i}$, where $r_i$ and $\omega_i$ are ...
1 vote
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### Why is there a phasor in the transfer function of an ideal LPF?

I'm learning about Low Pass Filters. My professor said the following is the transfer function of an ideal LPF: $$H_{LPF}(f) = G\Pi\left(\frac{f}{2B_{pass}}\right) e^{-j2\pi ft_0}$$ However, i don't ...
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### Relation between harmonics and quantization [closed]

I'd like to make digital samples that construct sine waves. It's nothing but direct digital synthesis (DDS) before the digital-to-analog converter and filter. I want to make a sinewave sample that ...
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### Output spectrum of the direct digital synthesis (DDS)

I have a question about the output spectrum of DDS, which consists of a phase accumulator and look-up table. Since the look-up table stores accurate information about sinusoidal waveform, I think ...
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### Issue with cudafft library and fftshift on odd image dimensions

I'm facing with a code I'm implementing for an exam using the GPU. Specifically, the code I'm writing is in C++, and I'm using the CUFFT library to perform the Fast Fourier Transform (FFT). The ...
33 views

### NUFFT of non-uniform sampling spectrometer

I am looking to apply Matlab's nufft.m function to a signal non-uniformly sampled with a spectrometer, hence measuring values at discrete frequencies. In this case I believe my sample points t will be ...
37 views

### Understanding frequency band specification in wireless networks

I am trying to clear my understanding of frequency bands. When a particular wireless network standard like WiFi 6 claims operation in the $2.4$ GHz or $5$ GHz band, what do these values refer to? I am ...
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### What is the cleanest, most transparent way to rapidly excite a resonant bandpass to a given amplitude (for musical synthesis)?

Background Music audio synthesis can be performed using underdamped resonant bandpasses as harmonic oscillators (set to harmonic frequencies of a given note). These can then be excited when input ...
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### What are the spikes here in the spectral analyser?

I'm learning to use the spectral analyser in Simulink, and tested it with a 500kHz square wave (sampled at 1MHz). When I set the Resolution Bandwidth (RBW) to 700Hz, the plot was beautiful and shows ...
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### Remove noise from lung sound wav

I am working in this dataset data.mendeley.com/datasets/jwyy9np4gv/3? aiming to develop a machine learning model for classifying various diseases based on lung sounds during both expiration and ...
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### What is the event that repeats itself in sinusoidal signals

I am studying medical imaging and it has been stated that it is sufficient for Nyquist Theorem to hold for the signal to be Bandlimited. I am trying to understand what is the wave in a signal. What is ...
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### Assumptions of Nyquist sampling theorem [closed]

Hoping I can save the question and it doesn't get migrated to philosophy stackexchange as Hilmar said in any case I don't think it is a different question the question was always meant to be ...
1k views

### Why is energy zero at zero bandwidth?

From the video lecture on noise analysis by Razavi here. Can anyone explain in more detail what Razavi said here? Why is the energy at a single frequency (zero bandwidth) zero? Lets look at the ...
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### Strange spectra of different volume sines

I am simulating mic input with a sine of 100 values that would, in q4_28 look like this (full period): ...
1 vote
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### Correction Factor for np.fft.rfft

I tested the function np.fft.rfft using the following code and determined the magnitude of a $50 \, \textrm{Hz}$ sine wave. ...
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### Is a bandpass filter superfluous when the frequency band of interest after applying the FFT is below the Nyquist frequency?

I have time-series data with a sampling rate of 1 Hz, hence the Nyquist frequency is 0.5 Hz. I am interested in the frequency band 0.01-0.1 Hz and I would like to apply a Periodogram to transform the ...
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### Derive PSD of an MA(1) process

Suppose there is a moving average process of order 1 that also includes a zeroth term thus: $$Y_t=\theta\left(B\right)X_t = \left(\theta_0+\theta_1B\right)X_t$$ where $X_t$ ...
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### Discontinuities in the frequency domain

I'm trying to implement a waveform such the frequency will look like this - $f(t)=f_0+\left(f_1-f_0\right) e^{\frac{\left(t \pm \delta_t / 2\right)^2}{2 \sigma^2}}$ To do so, I calculate it like this -...
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### Decomposing a signal so that the magnitude spectrum of the decomposed signals lie in some specific amplitude range

Suppose I have the following signal: I can compute its power magnitude spectrum: PSD = np.abs(np.fft.rfft(signal)) Now I would like to pick a specific amplitude ...
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