This is an objective method for measuring noise. It has primarily been used for steady state conditions, however, with increasing computer power, it is becoming increasingly common for it to be used for accelerations and decelerations. It is based on the use of the 25 1/3 octave bands between 20Hz and 12500Hz. The technique makes allowance for masking (a feature of hearing whereby frequencies can be swamped by a louder tone of a close frequency). The technique also weights the different 1/3 octave bands depending on their frequency and level (i.e. interpolating between the standard A, B and C networks as appropriate). In a similar way, the bands are assigned different widths, dependant on the relative annoyance of the bands (as opposed to the 'equal loudness' curves used for the A, B and C weightings).