BRUEL & KJAER 2032 Instruction Manual page 163

13.2.13. Signal to Noise Ratio
As with Coherence, the Signal to Noise Ratio can be used in conjunction with frequen-
cy response functions as an indication of the quality of the measurement. A small value
of 'Yis(k) or S/N (k) need not necessarily mean that the measured frequency response is
invalid. Where the cause of the small values is noise, more averaging may be done to
improve the measurement accuracy. The Signal to Noise Ratio is defined as:
S I GAB(k) 1
2
-(k}=_ - -
2
N GAA(k) · GBB(k)-1 GAB (k) I
'Yis(k)
1 - 'Y2 As(k)
Coherent Output Power
Non-coherent Output Power
The function is the real-valued and displayed as S/N (k) for 0
~
k
~
800 on a logarithmic
amplitude scale.
13.2.14. Coherent Output Power and Non-coherent Output Power
The Coherent Output Power expresses the power at the output due to the input:
Cop(k)
=
I GAB (k) 1
2
2
(k) -G (k)
=
'YAB . BB
GAA (k)
The Non-coherent Output Power expresses the power at the output due to system
noise:
- IGAB(k)l
2
(
2
) -
NCOP(k)
=
GBB(k)-
=
1
--yA 8
(k) · GBB(k)
GAA
(k)
The Coherent and Non-coherent Output Power are 1-sided real-valued functions dis-
played for 0 ~ k ~ 800. They can be displayed as:
RMS
Power
Power spectral density
Energy spectra density
They can be A-weighted.
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