# Tag Info

Accepted

### Before the fft2, why need fftshift for the kernel?

For the FFT, the origin is in the top-left corner, not in the middle of the image. If you create a kernel and pad it such that the origin is in the middle of the image, then compute the FFT, you will ...
• 1,346

### Get rid of DC offset by subtracting mean, but still have impulse at f = 0 Hz

1.- The way to remove signal DC is with series capacitance. Many Spectrum Analyzers, desktop/rack instruments, include internal DC block. However, additionally using a DC block right on the input port ...

### An new arranging of the discrete Sine transforms

1.- for any other reader not familiar with DST type 5 or DST-V, I'd like to include the definition of Discrete Sine Transform and types. Following a list with DST types 1 to 5, from https://planetmath....
1 vote

### Nyquist frequency Plotting Distortions

One way to avoid low time resolution is to upsample signals before whatever processing. To answer this question I have modified the Mathworks example that downsamples DAB (audio) signals to match DVD (...
1 vote

### Confused over Stopband attenuation and stopband ripple

Late to the party, not completely answering the OP, but will give guidance. Stopband ripple is a valid term, and answered by @Matt L. here And a good example here
1 vote

### Uniform density 2d peak detection of spectrogram

What about an heuristic? A 1D version of the algorithm that runs in $O(n \, log(w))$ iterations, where w is the size of the neighborhood considered can be obtained ...
• 1,801

### An new arranging of the discrete Sine transforms

Let's restate your problem as a linear equation Let $U_{ee}$, $U_{eo}$, $U_{oe}$, $U_{oo}$ be the partition of the $S$ matrix in even-odd row-column index, similarly $v_e$ and $v_o$ are the partitions ...
• 1,801

### Get rid of DC offset by subtracting mean, but still have impulse at f = 0 Hz

Take a close look at the spectrum of your signal minus the mean -- you should see that the bin at f = 0 is actually zero. But your original signal has a strong slope to it. When you take the FFT of ...
• 10.1k

### MATLAB 2D CA-CFAR not working on range doppler map?

Sorry in advance, this is not a complete answer (I don't have enough reputation to add a comment). First of all, I have some doubts about the calculation of $NT$. If you want to take a rectangle for ...
1 vote

### How can I use the FFT in MATLAB to get the time domain equation representation of an image?

I believe this is the same: How to get Fourier coefficients to draw any shape using DFT? It can be done, but it's going to be tricky coding. You'll first have to represent your image as a single ...
• 140

### How can I use the FFT in MATLAB to get the time domain equation representation of an image?

Sorry, can't be done. You can only derive equations for a small number of well defined shapes but if you take a close-up picture of the oak tree in my back yard, all bets are off. It will look mostly ...
• 35.6k
Accepted

### Is MATLAB command "fourier" only applicable for continous-time signals or is it also applicable for discrete-time signals?

I had never seen this fourier command before. From what I gather, it returns the expression for the Fourier transform of the input to the command, specified as a ...
• 1,955

### Is MATLAB command "fourier" only applicable for continous-time signals or is it also applicable for discrete-time signals?

Fourier is part of the Symbolic Math toolbox, so you use it to compute the closed form transform of a symbolic function. With any real discrete data, you need to ...
• 131
$3dB$ down is half power, and $6dB$ down is half amplitude; The average power value matches the power calculated using RMS voltage.