Topic:
What happens when you bulk shift by a fraction of a sample?

Description:
What happens, for example, if you have four mill data and in computation
manager/bulk shift you shift by 50 mills?  This is NOT an even multiple
of the sample rate.
 

Solution:
1.) IESX requires that the data have a sample at time = zero.
Hence if you shift by 50 mills the system inserts a sample at -52 mills.  
This is an even number of samples above time = zero.
 
2.) In order to shift the peaks and troughs by 50 mills the data
must be resampled.  For example, the original data (with a tfs
of zero) would have had samples at 96 mills and at 100 mills.
The peak might lie between those two samples, e.g.,  at 98 mills.  
When the system shifts the data it will also resample so that it has a 
value at 48 mills (This is an even multiple of the 4 mill sample rate.) 
and that value should be like the peak that was at 98 mills.  (98 minus
the 50 mill shift is 48 mills.)
 
Note that since data is resampled it is in some sense "distorted".
Ordinarily this should not matter.  However, there are situations,
e.g., when working with seismic inversion data, when this distortion
could be a serious problem.
 




Last Modified on: 29-MAR-99