SignalExpress

cancel
Showing results for 
Search instead for 
Did you mean: 

What does 'Subset and resampling' do while downsampling the data

I am curious to know how exactly 'Subset and Resampling' in signal express processing tab works while downsampling the data. So if I am gathering data at 1.7kHz and Resampling it at 1Hz using 'Subset and Resampling', how does signal express make 1 data point out of 1700 data points, is it random pick, or average? Help file says it interpolates to obtain resampled data, it would make sense for upsampling, but i am not sure how it works for downsampling. Any Ideas?


------------------------------------------------------------------------------------------------------
Kudos are (always) welcome for the good post. 🙂
0 Kudos
Message 1 of 4
(6,703 Views)

Hi odessy27,

 

From the help, Subset and Resample will downsample the signal if you specify a larger dt or df.  If you have a signal that has been sampled at 1.7 kHz, and you want to downsample to a 1 Hz signal, SignalExpress will take the samples of your signal at 1 Hz.  If there is not a sample at an integer multiple, then SignalExpress will interpolate between the two closest signals.

Regards,
Jim Schwartz
0 Kudos
Message 2 of 4
(6,692 Views)


jschwartz wrote:

Hi odessy27,

 

From the help, Subset and Resample will downsample the signal if you specify a larger dt or df.  If you have a signal that has been sampled at 1.7 kHz, and you want to downsample to a 1 Hz signal, SignalExpress will take the samples of your signal at 1 Hz.  If there is not a sample at an integer multiple, then SignalExpress will interpolate between the two closest signals.


Jim thanks for the reply. I think I should clarify my question a little more.  I am downsampling my data using the Subset and Resampling feature. My hardware (NI9239) limits minimum sampling frequency to 1.6kHz. I, then process data using scaling and conversion and adding filter (Both features does not reduce number of samples) the processed data then goes to subset and resampling where I spacify dt=1s, as a result number of samples are reduced from 1.6kSamples to 1 sample each second.

            So could this whole process flow be summerized as,  Acquiring Data each second (1.6kSamples)>>Scaling and Conversion(1.6kSmples)>>Filtering(1.6kSamples)>>Subset and resample(1sample) This?

If my interpretation of the process flow is correct, then how does the signal express convert 1.6kSamples of filtered data into 1 sample each second? Is it average of 1.6k Samples over one second, or the random picked sample out of 1.6k samples or 1600th/latest sample each second?  



------------------------------------------------------------------------------------------------------
Kudos are (always) welcome for the good post. 🙂
0 Kudos
Message 3 of 4
(6,690 Views)

Hi odessy27,

 

SignalExpress is not taking any averages - basically it is sampling your existing signal at 1 Hz.  If there is not a point at an integer increment, SignalExpress  will interpolate between two points.

Regards,
Jim Schwartz
0 Kudos
Message 4 of 4
(6,669 Views)