Lorentz/Gauss window

There are generally three types of peaks pure 2D absorption peaks, pure negative 2D dispersion peaks, and phase-twisted absorption-dispersion peaks. Since the prime purpose of apodization is to enhance resolution and optimize sensitivity, it is necessary to know the peak shape on which apodization is planned. For example, absorption-mode lines, which display protruding ridges from top to bottom, can be dealt with by applying Lorentz-Gauss window functions, while phase-twisted absorption-dispersion peaks will need some special apodization operations, such as muliplication by sine-bell or phase-shifted sine-bell functions. 

In more recent years new window functions have been introduced [15,16] that are similar to the Lorentz-Gauss window but which aim to improve resolution without a discernible reduction in sensitivity. These so called TRAF... 

The weighting functions used to improve line shapes for such absolute-value-mode spectra are sine-bell, sine bell squared, phase-shifted sine-bell, phase-shifted sine-bell squared, and a Lorentz-Gauss transformation function. The effects of various window functions on COSY data (absolute-value mode) are presented in Fig. 3.10. One advantage of multiplying the time domain S(f ) or S(tf) by such functions is to enhance the intensities of the cross-peaks relative to the noncorrelation peaks lying on the diagonal. 

Use the same series of data and follow the same procedure as before to try out the Lorentz-Gauss convert window type. There is one single parameter LB available to adjust the window. Set the initial value to LB = 0, increment and decrement its value in small steps and inspect the shape of the window using the interactive mode. Note that for LB > 0 the shape of the window is similar to the exponential window (signal-to-noise improvement) whereas for LB < 0 the window shape is similar to the sine-bell squared window. Try out a few values to enhance the signal-to-noise ratio and to improve the resolution, store the results and compare the spectra using the multiple display. 

Apodization is the process of multiplying the FID prior to Fourier transformation by a mathematical function. The type of mathematical or window function applied depends upon the enhancement required the signal-to-noise ratio in a spectrum can be improved by applying an exponential window function to a noisy FID whilst the resolution can be improved by reducing the signal linewidth using a Lorentz-Gauss function. ID WIN-NMR has a variety of window functions, abbreviated to wdw function, such as exponential (EM), shifted sine-bell (SINE) and sine-bell squared (QSINE). Each window function has its own particular parameters associated with it LB for EM function, SSB for sine functions etc. 

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