Apodisation

Apodisation (also known as weighting or window function) is mathematical operation that is applied to the free induction decay (FID) prior to Fourier Transform. It is used to improve data quality by removing noise due to FID truncation and to increase signal to noise or resolution by weighting different parts of the FID.

The exponential function accentuates the first part of the FID meaning that the resultant spectrum has higher signal but at the cost of resolution which is encoded later in the FID. The gausian function increases the resolution of the spectrum but at the cost of a decrease in the signal and distortions in the baseline. The sine bell function increases the resolution with again loss of signal but only minor distortions in the baseline.

NMRPipe manual pages for are available for exponential, gausian and sine bell window functions.