The main idea of signal smoothing is to avoid the low signal fluctuations. A great many false-positive peaks are likely to be found if the signal has not been previously smoothed and all the low resolution peaks removed. Therefore, this step should be taken before any peak detection algorithm is used. Even after applying noise reduction, we cannot rule out some of the detected peaks being due to noise perturbations, although this is minimized.
The most common signal smoothing technique is wavelet denoising proposed by [6,5]. It makes use of the undecimated wavelet transformation to estimate the wavelet coefficients. These are then used to denoise the signal and obtain a smoothed signal. There exists an online library, namely the Cromwell package, that includes all the denoising and smoothing functions. Figure 1 presents a small portion of the axis of one illustrative spectrum.