# Tag Info

Accepted

### Are integer multiples of a frequency in an FFT necessarily in phase?

If your signal is periodic but not a sine wave, than this might help. Every periodic function will have energy at the fundamental and it's integer multiples (the harmonics). Note that the fundamental ...
• 44.8k
1 vote
Accepted

### FFT2 to RFFT2 Fourier plane and similarities

Things are a lot simpler if we don't use so many fftshift calls. The RFFT for real-valued inputs produces the left half of the general FFT. This includes the zero ...
• 2,519

### Excel FFT of Two Sine Waves Not Giving Expected Results

As @Jdip mentioned, I had not constructed my original signal correctly. It turns out that I the time step for the two signals did not match when I computed them, hence what I was trying to take a FFT ...
• 157

### FFT2 to RFFT2 Fourier plane and similarities

Running the following code gets me quite close. ...
• 833
1 vote
Accepted

### Excel FFT of Two Sine Waves Not Giving Expected Results

Not sure what your signal looks like, I'm guessing it isn't constructed appropriately. In any case, here is a snapshot of the results on my end. You can see the correct spikes at 440 and 880 Hz. You ...
• 6,085
Accepted

### Peak FFT Frequency Off By One Bin

The problem seems to stem from the number of bins with data. Originally, I generated a time domain signal with 100 values and padded with zeroes to 128, the next power of 2. This gave me the problem ...
• 157

### Peak FFT Frequency Off By One Bin

There's a thing called "Fencepost error" or "Off-by-one error" and it's because them folks at Mathworks have apparently never read Dijkstra. I'm really grumpy about the topic, ...
Accepted

### Ignoring Negative Frequencies from FFT on Real Time Series Seems Inconsistent With Time Series

I appreciate your efforts in describing your problem in such details. I almost feel bad for the time it must have taken you! But it looks like by writing your question, you got to the answer yourself. ...
• 6,085
1 vote
Accepted

### Binning and Frequency for FFT on Financial Time Series Data

As far as using the FFT to analyze financial data; that really depends on what you are looking for. The FFT can give an indication of cyclical patterns if they exist. The FFT for bin 0 should not ...
1 vote

### Minimum amount of data needed for low pass filter on real time sensor data

A linear filter will usually produce output with only a single input sample. The «validity» of early output depends on the degree of filtering and what analysis you are doing on the output. Sometimes ...
• 3,394

Top 50 recent answers are included