"firstcranialnerd" <firstcranialnerve@yahoo.com> wrote in 
news:Ju6dnbCWAv0YDFXYnZ2dnUVZ_sCinZ2d@giganews.com:

> Hi, 
> I am looking at some simulated heart rate data and it is unevenly sampled
> events, so I resample the data at say 4Hz or 7Hz or thereabouts. When I
> take the fft of the resampled data (it has been zeromeaned, filtered,
> hamming windowed etc) I see a huge amount of noise, especially from
> approximately .01 to 1Hz. Does anyone know if this Low frequency noise is
> due to the resampling process? If so, how is it related and how could I
> remove it? Any help would be great. Let me know if I need to clarify
> anything. Thanks. 
> 
> 

How are you sure its not signal?  For example, heart rate will change with 
respiration, which will probably be around 0.2 Hz or so.  Every heart beat 
will change the heart rate somewhat, as you're probably estimating by 
1/period-- hence the 0.8-1Hz component.  I'd recommend working with 
simulated data to help understand what's going on.  

-- 
Scott
Reverse name to reply

firstcranialnerd wrote:

> Hi, 
> I am looking at some simulated heart rate data and it is unevenly sampled
> events, so I resample the data at say 4Hz or 7Hz or thereabouts. When I
> take the fft of the resampled data (it has been zeromeaned, filtered,
> hamming windowed etc) I see a huge amount of noise, especially from
> approximately .01 to 1Hz. Does anyone know if this Low frequency noise is
> due to the resampling process? If so, how is it related and how could I
> remove it? Any help would be great. Let me know if I need to clarify
> anything. Thanks. 

This could be an artifact of the digital filtering. Are you using any of 
IIR highpassing or like?

Vladimir Vassilevsky

DSP and Mixed Signal Design Consultant

http://www.abvolt.com

Hi, 
I am looking at some simulated heart rate data and it is unevenly sampled
events, so I resample the data at say 4Hz or 7Hz or thereabouts. When I
take the fft of the resampled data (it has been zeromeaned, filtered,
hamming windowed etc) I see a huge amount of noise, especially from
approximately .01 to 1Hz. Does anyone know if this Low frequency noise is
due to the resampling process? If so, how is it related and how could I
remove it? Any help would be great. Let me know if I need to clarify
anything. Thanks.