## Topic: Noise floor calculation from fft ouput (Read 2186 times)previous topic - next topic

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• ksr
Noise floor calculation from fft ouput
##### 30 March, 2012, 05:03:39 AM
Hi guys,

Can anyone explain me ,how to calculate noise floor value from fft output?

• saratoga
Noise floor calculation from fft ouput
##### Reply #1 – 30 March, 2012, 10:52:28 AM
Hi guys,

Can anyone explain me ,how to calculate noise floor value from fft output?

FFT of what exactly?  Usually the noise floor is calculated the same in the time and frequency domain: take the mean or standard deviation of the output when no signal is present.

• ksr
Noise floor calculation from fft ouput
##### Reply #2 – 02 April, 2012, 12:59:24 AM
[quote name='saratoga' date='Mar 30 2012, 20:22' post='791053']
[quote name='ksr' post='791032' date='Mar 30 2012, 05:03']Hi guys,

Thanks bro for your reply.The fft output of a single tone and multiple tone.For single tone and also for multiple tones ,am averaging all the peak amplitudes except the values at the given frequencies.I dont  know whether my approach is wrong or right...

• Garf
• Developer (Donating)
Noise floor calculation from fft ouput
##### Reply #3 – 02 April, 2012, 04:13:23 AM
This won't work very well due to spectral leakage, which will increase the floor in frequencies near, but not at, the tone. Why do you need a tone anyway?

• ksr
Noise floor calculation from fft ouput
##### Reply #4 – 02 April, 2012, 05:04:50 AM
This won't work very well due to spectral leakage, which will increase the floor in frequencies near, but not at, the tone. Why do you need a tone anyway?

I tried calculating SNR, THD, NOISE FLOOR, but what ever i have studied theoretically and calculated practically doesn't seem to match with the spectra lab result.