I am new to working with Bruker-style NMR data and am experiencing confusion with regard to Bruker's digital filtering. Some experiments on our Bruker spectrometers result in valid decim/dspfvs/grpdly values in the acqus output file, but other spectrometers give a value of -1 for grpdly. Does anyone know what this value means? More importantly, how can I calculate how many points to left-shift the Bruker fid for offline processing when grpdly does not contain the value?
asked Nov 11 '10 at 06:06
My understanding is that before Topspin 2.1 the number of left-shift points was determined through a combination of DECIM and DSPVFS values - so maybe older spectrometers will use this and set GRPDLY as -1.
Post Topspin 2.1 GRPDLY is the flavour of the day and is the value for t=0 given in complex data points. The first order phase correction related to the digital is thus GRPDLY * 360o
When you have no GRPDLY I find using something like the 'bruker' script in NMRPipe will help you out, or maybe even using the avance phase feature in Azara.
Hope that makes sense! Best Wishes, Dan
answered Nov 11 '10 at 08:45
My understanding is that the GRPDLY parameter was added with the introduction of the Digital Receiver Unit (DRU). I'm not sure what XwinNMR/TopSpin release that correspondes to. Previous to this, there was a look-up table based on the DECIM and DSPVS parameters. I can send you a copy of this table, if you like.
On newer Bruker systems, using the "BASEOPT" digital filter will result in a very flat baseline with no "smilies" and zero (or very close to zero) residual first order phase correction simply by using the first order phase correction value optained by multiplying the GRPDLY parameter by 360.
answered Nov 15 '10 at 09:10