Re: filtering out harmonic trend

[Francesco Potorti`]

>> I have a 200,000 samples measurement, which is a sort of noise with
>> bandwidth in the order of the inverse of 500 samples.  Superimposed to
>> this noise there is a very slow sinusoid with a period of about  
>> 300,000
>> samples.  This means that my measurements do not even see a complete
>> cycle of this sinusoid.
>>
>> I want to estimate the sinusoid (in order to remove it from the
>> measurement).  So I need some sort of very-low pass filter.  However,
>> usign a simple causal low-pass filter would give me a delayed output.
>> Can anyone suggest some keyword for a noncausal filter to look for?  I
>> guess that it could be simple, because the bandwidths of signal and
>> noise are so far away each other.
>
>If the low-frequency signal is a 'clean' sinusoid, then I'd try  
>fitting a sinusoid to the data, and then subtract this sinusoid from  
>the data.

After some experimentation, it turns out that my low-frequency signal
is not a sinusoid.  So I stuck with filtfilt.  Now, I am deciding what
filter to use and how to choose its parameters.

Thank you

-- 
Francesco Potortì (ricercatore)        Voice: +39 050 315 3058 (op.2111)
ISTI - Area della ricerca CNR          Fax:   +39 050 315 2040
via G. Moruzzi 1, I-56124 Pisa         Email: address@hidden
Web: http://fly.isti.cnr.it/           Key:   fly.isti.cnr.it/public.key