FID Shift

Use this command located under the 'Processing/More Processing' menu of Mnova to right or left shift the FID.

Shifting the FID to the left or to the right is equivalent to shift the phase of the frequency domain spectrum by –wt0.

From a practical point of view this means that if the FID is shifted by one point to the right, the resulting f-domain spectrum will have a linear phase correction of -360º. The same effect, but with the opposite sign occurs if the FID is shifted to the right.

This phenomenon is very easy to understand by considering the well-known property of the Fourier Transform of a Time Shifted Signal which can be stated as:

The Fourier transform of a signal which has a simple time shift is:

i.e. the original Fourier transform but shifted in phase by –wt0

For example: if you type -10 in the edit box, this will be equivalent to apply a linear phase correction of +10*360º.

Basically, in this example, Mnova will not take into account the first 10 complex points of the original FID; shifting the origin of the new FID 10 points to the left and adding 10 zeroes to the end (i.e., left shift 10 points). Clicking on the Cyclic check box will add the original first points to the end of the FID (instead of zeroes).

Here you can see an example of a FID which needs to be shifted +11 points: