final surface finish is given to the road surface again in the case of the float the protrusions 25 are spaced in accordance with the pseudorandom pattern desired in both these cases the tool is drawn transversely across the road surface and then indexed at the appropriate point so that there is no overlap in the tooled grooves in the road surface since there are practical limitations to the width of the head of the rake or float one could make a set of tools that consist of a set of rakes or floats that each had a unique pseudorandom pattern for example if one could make a rake or float with a head width limited to 6 feet and the average pitch distance between grooves was set at 2 inches then one tool rake or float could realize a pattern that was limited to 6 ft u00d7 12 u2033 1 ft u00d7 pattern length 2 in 36 grooves since in this example one rake or float is capable of providing a pattern which is relatively short one could envision a set of three that would provide a unique and non repetitive pattern of 36 u00d7 3 108 grooves it can be shown that patterns of this length can provide sufficiently uncorrelated acoustic spectra to be useful ultimately the longer the pattern the more noise like the acoustic spectrum a third approach to obtaining the desired pattern would be to use an embossing or stamping process.