Linked Questions

117 votes
4 answers
53k views

Why is it a bad idea to filter by zeroing out FFT bins?

It's very easy to filter a signal by performing an FFT on it, zeroing out some of the bins, and then performing an IFFT. For instance: ...
endolith's user avatar
  • 15.7k
26 votes
4 answers
9k views

FIR Filter Design: Window vs Parks McClellan and Least Squares

Are there any advantages to use a window approach over Parks-McClellan (further abbreviated here as PMcC) or Least Squares algorithms for FIR filter design of a low pass filter? Assume with today's ...
Dan Boschen's user avatar
  • 50.3k
14 votes
4 answers
7k views

Intuition for sidelobes in FFT

I was wondering if there's a intuitive way to understand why sidelobes appear when performing an FFT on a signal of fixed length?
CatsLoveJazz's user avatar
30 votes
3 answers
21k views

What should be considered when selecting a windowing function when smoothing a time series?

If one wants to smooth a time series using a window function such as Hanning, Hamming, Blackman etc., what are the considerations for favouring any one window over another?
babelproofreader's user avatar
9 votes
3 answers
32k views

Number of DFT (FFT) Points Required for a Specific Frequency Resolution for an Oversampled Signal

I have a bandpass signal centered at 2 MHz and bandwidth of 50 kHz (the signal frequency varies from 2 MHz - 25 kHz to 2 MHz + 25 kHz). This signal is being sampled at 10 MHz. I want a frequency ...
Vinod's user avatar
  • 644
14 votes
2 answers
30k views

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 ...
argh's user avatar
  • 173
13 votes
2 answers
7k views

Why would one use a Hann or Bartlett window?

Suppose we're designing a low-pass FIR filter, and I want to use one of these three windows: Bartlett, Hann or Hamming. From Oppenheim & Schafer's Discrete-Time Signal Processing, 2nd Ed, p. 471:} ...
Tendero's user avatar
  • 5,020
3 votes
2 answers
15k views

Magic of twiddle factor in DFT

In DFT calculation following formula is used $$X[k] = \sum_{n=0}^{N-1} x[n] e^{-j2\pi\frac{kn}{N}}$$ where the Twiddle factor is known as complex root of unity, that is a complex number $W_N$ such ...
user6363's user avatar
  • 333
1 vote
2 answers
2k views

Different way to separate a particular frequency from a signal

Let's say I have a signal which is composed of 2Hz,10Hz,17Hz,19Hz and 25Hz discrete time sinusoidal waves and I need to allow only 17Hz component to pass. As far as I know, the standard way to ...
Ritik Madan's user avatar
10 votes
1 answer
11k views

What happens when N increases in N-point DFT [duplicate]

I am curious about DFT, and I wrote a simple MATLAB code to test what happens when $N$ increases. I took a rectangular signal with length $L=15$, an then found th DFT of 16, 32 and 64 points. I looked ...
Canberk's user avatar
  • 161
0 votes
1 answer
2k views

Specific Frequency Resolution

I have an audio signal SampleRate Fs: 44100 Hz TotalSamples: 94144 samples Duration t: 2.1348 s The frequency resolution is given by ...
Learthgz's user avatar
  • 132
0 votes
1 answer
1k views

FFT and number of samples relations

I am new in signal processing. I generated a signal with $f_{in}=10 \mathrm{kHz}$ and also take 64 sample from this signal after doing some process in an ADC block. I want to convert the result to the ...
saleh's user avatar
  • 1
-1 votes
1 answer
5k views

Aliasing after downsampling [duplicate]

Let me start with time domain representation of the original signal \begin{equation} x_n=\sum_{k=0}^{2N-1}X_ke^{j\frac{2\pi nk}{2N}} \end{equation} where $2N$ is number of time/frequency samples ...
Cali's user avatar
  • 181