The rating of impact sound insulation on the basis of tapping machine measurements with the ISO reference values has proved to be unsatisfactory in practice. This is mainly due to the differences in spectrum shape of tapping machine noise and real life impact noises, such as walking. The problem can be solved by changing the reference values in accordance with these differences in spectrum shape. The difference between tapping and walking noise spectra has been established by measurements on 49 different floors. In the most important frequency range (125-500 Hz) it was discovered to be sufficiently constant for all the floor constructions considered. Thus a new set of reference values has been derived, based on the assumption that the NR-curves provide a correct subjective rating system for walking noise. In addition, due account has been taken of the different frequency content at higher frequencies of impact noises other than those made by walking males, such as those made by walking females, jumping children, the moving of furniture, etc. © 1976.