The European Directive 2002/49/EC defines useful procedures in order to evaluate, by means of indexes, the acoustic pollution affecting urban areas. To apply those methods correctly, it is necessary to get a properly designed acoustic database. Usually the environmental information managed by the laboratories shows a different kind of problem. Nowadays the Acoustic Laboratory of the University of Cadiz (Spain) is very interested in the developing of new data-processing tools. These tools overcome the errors in the calculation of the indexes due to the use of inappropriate databases. We focus not only on the determination of the possible problems, but on the best solutions. We suggest in this paper a simple data treatment method that permits one to reach more accurate indexes in spite of such common problems.