NMRPipe Processing Functions
CBF: Constant Baseline Correction Using Signal-Free Regions.

CBF is intended to remove constant offsets in data, particularly in the time domain, since an offset in time-domain data will lead to a spike at zero frequency in the corresponding spectrum.

CBF calculates and subtracts a constant from each 1D vector in the data. The constant is calculated from the average of a range of points in the vector. The range of points is specified as a percentage of points to use from the tail (last points) of each vector. CBF includes special handling for depending on the vector data type:

• If the vectors are complex, the real part and imaginary part are each treated separately.
• If the vector data type is sequential (old-style Bruker pseudo-complex data), then odd points and even points are treated separately, as if they correspond to real and imaginary data respectively. This special handling can be suppressed with the -noseq flag.
• If the vector data type is oversampled time-domain data which was not corrected during conversion (e.g. bruk2pipe -AMX instead of -DMX), no constant will be subtracted from the initial ~70 oversampled points. The number of oversampled points is calculated automatically according to the conversion parameters.

OPTIONS

-last percent
This option specifies the number of points to use for calculating a correction, as a percentage of the vector size. By default, this value is 10, which means that the last 10% of points in each vector will be averaged to find a constant for subtraction.

-reg reg1StartPtsX reg1EndPtsX ...
This option can be used to restrict the correction to a particular range of points within each vector, with the starting and ending points specified as points, or with labels Hz ppm %. By default, the calculated constant is subtracted from the entire vector.

-slice reg1StartPtsY reg1EndPtsY ...
This option can be used to restrict the correction to one or more particular ranges of vectors within each plane, with the starting and ending locations specified as points, or with labels Hz ppm %. By default, all vectors are corrected.

-noseq
Suppress special handling of sequential mode time-domain data.

-nodmx
Suppress special handling of uncorrected oversampled time-domain data.

EXAMPLES

CBF is commonly used as the first processing function in a transform scheme, as shown here, where it is used to remove a DC-offset in a 2D magnitude-mode FID.

nmrPipe -in test.fid \
| nmrPipe -fn CBF \
| nmrPipe -fn SP -off 0.0 -end 0.95 \
| nmrPipe -fn ZF -auto \
| nmrPipe -fn FT \
| nmrPipe -fn TP \
| nmrPipe -fn SP -off 0.0 -end 0.95 \
| nmrPipe -fn ZF -auto \
| nmrPipe -fn FT -neg \
| nmrPipe -fn MC \
| nmrPipe -fn POLY -auto -ord 0 \
   -out test.ft2 -ov