| T O P I C R E V I E W |
| physcool |
Posted - 11/06/2013 : 7:59:06 PM
Origin Ver.8 and Service Release (Select Help-->About Origin):
Operating System:windows 7
Hi
I have a problem in performing FFT. I need to do FFT on a data set with x from -5 to +5 with 10000 data points. I need to get amplitude vs frequency data. When I perform FFT, the origin automatically select sampling rate, and the resulting frequency step is very large (somewhere ~0.05). I need to get FFT amplitude data with better resolution of frequency(smaller frequency steps to have more data points in a given range of frequency) since I need to get FFT amplitude at low-frequency regions below 1. If I manually change the sampling rate, it changes frequency steps, but it just shrinks the frequency range and results do not make sense. Can you help me on this to produce higher resolution FFT data within a given frequency range? Thank you very much. |
| 1 L A T E S T R E P L I E S (Newest First) |
| Drbobshepherd |
Posted - 11/08/2013 : 12:29:25 PM
To increase the frequency resolution of your FFT, you have to increase the time of your sampled data. To double the resolution, increase the x-range from -10 to 10, setting y=0 for -10< x <-5 and 5 < x <10. Then execute the FFT. This is a well-known technique called zero padding.
Note: High-frequency spikes may result from this. To prevent this from happenning, apply the apodization window before padding the data with zeros.
Let me know if this works. |
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