Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2016, Tutor: Josep Maria Solanes MajúaWe are interested in detecting the possible impact of the environment in which the galaxies reside on their spectra. With this aim, we have implemented a stacking technique for the calculation of average spectra of galaxies with high signal-to-noise ratio (S/N) and resolution, as well as an extinction-corrected local density estimator. We use the huge dataset of ~ 1; 500; 000 homogeneous optical spectra reduced and published in the Sloan Digital Sky Survey Data Release 12 inside the limits of the Legacy Survey. Our methodology is tested against the class of galaxies with measured Hα emission, finding important differences in the continuum and in the heights of the principal emission lines.