The random test spectrum to be utilized in a
particular test program is described in the appropriate test specification. It
will generally be specified in terms of g^{2} /Hz in flat areas of the spectrum, and in terms of dB per octave slopes in other (varying amplitude) areas. For example, the test spectrum used exclusively in this procedure in examples is specified as follows:
Frequency
Band 

Spectrum
Density 
20 to 80 Hz^{ } 80 to 350 Hz^{
} 350 to 2000 Hz^{ } 

+3 dB/oct rise to
.04g^{2}/Hz
0.04g^{2}/Hz 3 dB/oct roll off from
.04g^{2}/Hz 
Overall Grms = 6.0 
For convenience in performing the subsequent
synthetic random voltage calculation the required test spectrum can be put in
logarithmic terms (dB) specified for each of the bandwidths used in the random
equalization system. This is accomplished by assigning a positive dB value to
the highest spectral density amplitude. The dB value should be chosen high
enough so that the lowest amplitude value can still be represented by a
positive dB value. (This will avoid sign mistakes in the calculations). For
the sample spectrum above a value of + 10.0 dB was designated for
0.04g^{2}/Hz and the spectrum in dB is determined
graphically or by formula as shown in Figure 46. The dB value determined for
the center frequency of each filter bandwidth is tabulated in column H as
shown in Figure
43 .