A&D RA3100 Omniace, Instruction Manual

Page: 132 / 176

10. 10Appendix - 10.4. FFT Analysis
132 1WMPD4004444
Transfer Function (Two Signal Analysis)
The transfer function indicates the frequency characteristics of the input and output of the transfer
system.
It is derived as the ratio of the cross power spectrum Gyx and input (reference) power spectrum Gxx.
Transfer function = Hyx = Gyx/ Gxx
Real number part Lin-Rel
HRyx
Imaginary number part Lin-Img
HIyx
Amplitude Lin-Amp
�𝐻𝐻𝑅𝑅𝑅𝑅𝑅𝑅 2 + 𝐻𝐻𝐼𝐼𝑅𝑅𝑅𝑅 2
Logarithmic amplitude Log-Amp
10 × log(HRyx
2
+ HIyx
2
)
Phase Phase
tan
−1
(HIyx/HRyx)
Coherence Function (Two Signal Analysis)
Expresses a comparison of the power caused by the input signal of the transfer system and the total
output power.
It is derived from the cross power spectrum Gyx, input (reference) power spectrum Gxx,
and output (comparison) power spectrum Gyy.
Amplitude Lin-Amp
| 𝐺𝐺𝑅𝑅𝑅𝑅 |
2
/(Gxx × Gyy)
NOTE
The coherence function equals 1 across the entire frequency with a single measurement. Make sure to
perform averaging of the frequency axis.
Octave Analysis
1/1 octave band or 1/3 octave band analysis can be performed.
This product derives the power spectrum first and then adds the data in each band range.
Amplitude Lin-Amp
Oct x k1
Logarithmic amplitude Log-Amp
10 x log(Oct x k1)
k1: Window function BW compensation coefficient
Rectangular 1
Hanning 0.666
Hamming 0.731