Algorithm peak-picking

In this dialog box the Peaks sign, the Peaks Label and the parameter PC, which determines the sensitivity of the peak picking algorithm may be specified. Furthermore, the Interpolation and Multiplicity mode can be set which increases the accuracy of the peak picking and lists the multiplicity information respectively. 

Figure 6 Results of a peak picking algorithm. At x = 80, the first derivative spectrum crosses zero and the second derivative is negative. A 9-point cubic least-squares fit is applied about this point to derive the coefficients of the cubic model. The peak position (dytdx = 0) is calculated as occurring at x = 80.3...

It proved impossible to derive consistent area or height information from repeat runs using either visual methods, or standard peak-picking algorithms. Reliable quantitative calibration curves could only be derived from evaluation of the slope of the phase angle difference curve as a function of time at a fixed arbitrary point near the beginning of the heat evolution. 

Andreev VP, et al. A uiversal denoising and peak picking algorithm for LC-MS based on matched filtration in the chromatographic time domain. Anal Chem 2003 75 6314-6326. 

Signal-to-noise criteria are commonly employed as part of peak picking algorithms. 

Andreev, V.P., Rejtar, T., Chen, H.S., Moskovets, E.V., Ivanov, A.R., Karger, B.L. (2003) A universal denoising and peak picking algorithm for LC-MS based on matched filtration in the chromatographic time domain. Anal. Chem. 75, 6314-6326. 

The result that is reported as the peak wavenumber is frequently the wavenumber value of the maximum discrete point, which rarely corresponds to the exact center of the band. It is not uncommon for these values to be reported to four or five decimal places, as this is how well the wavenumber of each datum is recorded however this number of digits is well beyond the realistic accuracy of most experiments. The use of the maximum data point for the wavenumber position of a band is suitable only for noncritical information. The actual band center may be considerably displaced from the maximum data point. For example, in a typical spectrum measured at 4-cm resolution, data points are typically computed at 2-cm intervals. Under these conditions simple peak-picking algorithms would not readily detect band shifts of about 0.5 cm . In practice, the wavenumber of the maxima of bands in the spectra of condensed-phase spectra measured at a resolution of 2 or 4 cm should only be reported to 1 cm . ... 

Peak-picking appears to be a domain largely occupied by instrument manufacturers. As a consequence, many of the algorithms remain unpublished. 

The role of peak-picking is to return only one position per peak, and in the presence of noise, this again poses problems. It is likely that most algorithms will start from a position of intensity maximum, and then search either side for the first point significantly lower, i.e., a multiplier of the noise. This defines a new peak region and the process could then be repeated. Some software additionally offers the facility of a horizontal threshold, above which values are returned and below which they are not. 

Wiithrich et al published a tour de force on the Automated Peak-Picking and Peak Integration in Macromolecular Spectra (AUTOPSY). This work deals primarily with two-dimensional spectra, but the algorithms are equally... 

In addition to providing automated peak picking and computation of the corresponding chemical shift lists, APSY supports automated sequential resonance assignment. Thus, APSY is a valid alternative to related NMR techniques. APSY can be the first step, after sample preparation, in a fully automated process of protein stmcture determination by NMR with successive automated algorithms for the NOESY spectrum analysis and structure calculation. 

In the case of absorbance or Raman spectra usually the maxima are of interest, whereas for transmittance or reflectance spectra the minima are the important features. This can be accounted for by selecting the appropriate peak picking mode on the Mode page (Fig. 11.17). If you mark Automatic in the Direction of Peaks box, the spectrum type information stored in the data block is used to determine whether maxima or minima are picked. In rare situations, e.g. for subtraction, it is necessary to specify whether the algorithm should pick for minima or for maxima. 

On the Mode page you also have to decide the algorithm for peak picking. 

Modification is performed by separating the harmonics from the spectral envelope, but this is achieved in a way that doesn t perform explicit source/filter separation as with LP analysis. The spectral envelope can be found by a number of numerical techniques. For example, Kain [244] transforms the spectra into a power spectrum and then uses an inverse Fourier transform to find the time domain autocorrelation function. LP analysis is performed on this to give an allpole representation of the spectral envelope. This has a number of advantages over standard LP analysis in that the power spectrum can be weighted so as to emphasise the perceptually important parts of the spectrum. Other techniques use peak picking in the spectrum to determine the spectral envelope. Once the envelope has been found, the harmonics can be moved in the frequency domain and new amplitudes found from the envelope. From this, the standard synthesis algorithm can be used to generate waveforms. 

This has a number of advantages over standard LP analysis in that the power spectrum can be weighted so as to emphasise the perceptually important parts of the spectrum. Other techniques use peak picking in the spectrum to determine the spectral envelope. Once the envelope has been found, the harmonics can be moved in the frequency domain and new amplitudes found from the envelope. The standard synthesis algorithm can be used to generate waveforms from this. 

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