Construction of hybrid simulated/real spectra for testing preprocessing programs. (top) Clean, pure protein component spectrum with no noise and no baseline simulated using SimSpec 2.1 MALDI/SELDI simulation engine. Arrows over peaks show the m/z values of the virtual proteins. (middle) Buffer+matrix spectrum generated in a SELDI PBS IIc, representing noise, baseline, and artifacts that are typically seen. (bottom) Final hybrid spectrum, consisting of the sum of simulated and real components. Hybrid spectra have the advantage of having diverse signal components (150 virtual proteins) with exact knowledge of the virtual proteins while retaining the true noise and baseline characteristics from real SELDI data.