Real Spectra and Noise

In contrast to digitally generated bands, real spectra - signals received from a spectrophotometer - are composed of the actual signal, caused by absorbance of the substance, and noise (Fig. 2-21 a). Noise is the generally higher-frequency variation of the 

Disturbing signals may lead to systematic or statistical errors. A detailed analysis of these errors is given by O Haver et al. [47], and [51-53] also see [33] and [54-57]. An important quantity for characterizing the quality of spectrum is the ratio 

The statement that the SNR decreases with the nth power of two n = derivative order) [52, 59] is a rule of thumb and is only true for a smoothing ratio of about 0.25 [58]  

AA distance of data points in digital derivatives n number of data points of digital smoothing 

According to Eq. (2-60) the SNR becomes dramatically smaller with increasing derivative order. This effect becomes intensified in flat bands, where FWHM is high. 

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