Recovery of SSP input parameters with PPXF versus S/N of the spectrum. We use four different SSP templates (as indicated by different colours) from the E-MILES library and add artificially Gaussian noise. The noisy spectrum is then fitted with PPXF. For each S/N, we repeat this with five noisy spectra and show the difference between the input parameter and the mean values of these five trails and their standard deviation. The vertical lines indicate the threshold S/N values of ten and three that we chose for reliable measurements of metallicities and velocities, respectively.