Filtering noise from a sinewave,how to corrected the phase and ampltitude

[yanhuaguang for china]

my signal is harmonic signal,I want to do FFT analysis
but my signal contain the white noise ,my question is:
1.which filter should i using?
2.how to corrected the the phase and ampltitude after filter the Filtering noise .

[AndrewM]

Hello,

The type of filter really just depends on what type of signal you are bringing in and what type of hardware you are using.

I would first take a look at where your noise floor is compared to your signal. If you are seeing too high of a power level in your noise, you can always apply a gain to you signal.

As far as filters, it depends on what frequency. If you are getting white noise across the frequency spectrum, then it will be harder to filter that out. If the noise is at a higher frequency (guassian is usually higher frequency), you could use a simple low pass filter.

Regards,

Andrew Mierau
Applications Engineer
National Instruments

[Ian_Ren]

To answer your second question, you can avoid phase shift by filtering the data twice, one from start to the end, and then from the end to the start. The following is how you do it

1) First, filter the signal using whatever filter that is appropriate.
2) Revers the data (array)
3) Filter the data again using the same filter
4) Revers the data again.

The phase shift should be cancelled out from the two filtering steps.

If you use the butterworth filter, you may not need amplitude correction. Anyway, it is easy to correct the amplitude even if you do need it, since the property of the butterworth filter is well defined.

You may have to throw away some data at the beginning and at the end of your data because of the filtering effects.

Hope this help
s.

Ian Ren

Roush Industries, Anatrol Division.