Linear baseline correction

Linear baseline correction

NUTS has several commands for correcting baselines that need only DC correction and/or linear tilt. (DC refers to an offset of the spectrum's baseline from true zero that is not dependent on frequency; in other words, the entire spectrum has the same offset.) In most cases, the baseline also has curvature, so linear correction is not sufficient, and a polynomial correction is necessary.

BC -- Baseline Correction

If the data is frequency domain data (spectrum), this command averages the first and last 64 points of the real half of the data and removes the DC bias and linear tilt between the start and end. This may or may not be sufficient to give good integration.

Note that this command acts differently if the current data is time domain data (an FID).

BF -- Baseline Flatten

This removes the DC component of the baseline and any linear tilt within the Zoom frequency limits. This is done by averaging points at each end of the zoom region, the adjusting so that these average values are at zero. The user can set the number of points to be averaged (with 2A) or use default values.

Data outside the Zoom frequency limits are adjusted, with DC correction only, to remain continuous with the Zoom region (see also FR). Note that the display does not need to be expanded to apply BF. The region just needs to be defined with the cursor or with Zoom subcommand F. The same operation as BF can be performed within the Zoom subroutine using the B subcommand.
See example of BF application.

FR -- Flatten Region

This command is almost the same as BF, with one exception:
In contrast to BF, data outside the Zoom frequency limits is not changed. This can result in discontinuities in the baseline at both ends of the Zoom region. One situation in which this is preferable is when baseline correcting and integrating selected regions of a spectrum. The FR command can be used to correct a chosen region, without affecting integrals in any other part of the spectrum.
See example of FR application.

2A -- Number of points to average

Lets the user control how many points are used to by the BF and FR commands. An entry of zero lets the program automatically determine the number of points to average, according to the following:
If the selected region is more than 256 points then 16 points are used for averaging.
If the selected region is less than 256 points and greater than 64 points then 8 points are used for averaging.
If the selected region is less than 64 points and greater than 16 points then 2 points are used for averaging.
If the selected region is less than 16 points then the end points are used directly without averaging.
If the number of points set by the user is greater than the entire selected region then the entire selected region is averaged.

This can be set in a macro using Set Points_to_average.

BR -- Baseline correct Bruker digitally filtered data

This command performs an operation similar to BC, but ignores the extreme ends of the spectrum when choosing points on which to base the correction. This is needed with digitally filtered data, due to the distortion of the ends of the spectra. By default, 2% of the data points at each end are ignored. See details, including description of additional options.

JE -- Baseline correct JEOL digitally filtered data

This performs the same operation as the BR command, but discards 5% of the data points at each end, instead of 2%, as with BR.