SV 977D User Manual - Appendixes
Uncertainty of the audibility ΔL
i
, σ
i
Using the Gaussian uncertainty propagation principle, the uncertainty of the audibility could be found as:
where index i corresponds to the spectral lines around a tone, and index j corresponds to the next tone under
investigation.
F.2.4. Grouping the tones
If a number of tones are present in a critical band, then their tone levels, L
Tm,n
(run index n across all tones in
the critical band; H is the number) are summed in terms of energy (equation (C.13)).
where
H is the total number of all tones in the critical band,
L
Tm,n
is the tone level with the run index m across all audible tones and the run index n across all tones in the
critical band, in decibels (dB).
This tone level, L
Tm
is used to recalculate the decisive audibility of the critical band.
NOTE 1. It is possible for the energy of individual spectral lines to be assigned to a number of neighbouring
tones at the same time. Upon addition of the tone levels of neighbouring tones, the energy of these individual
spectral lines may not be summed more than once.
NOTE 2. If the exactly 2 tones appear in one critical band, then they evaluated separately if both lie below 1000
Hz and their frequency difference exceeds certain value, determined in the standard, then the human ear can
distinguish them separately.
F.2.5. Calculation of the mean audibility, ΔL, and the extended uncertainty, U, of a
number of spectra
When the several averaged spectra are measured, their maximum tone’s audibility shall be averaged and the
extended uncertainty is calculated.
In each measured spectrum the maximum tone audibility and its uncertainty are chosen for the post-processing
step. This audibility is called the decisive audibility of a particular spectrum.
Mean audibility is calculated as shown in the equation (C.14).
where ΔL
j
is a decisive audibility of each spectrum and corresponds to the most audible tone.
The extended uncertainty is the uncertainty of the coverage probability region. In this standard the 90%
coverage was assumed, hence the coverage factor of 1,645 have to be used. To receive the value of it, the
mean averaged estimated value of all sigma shall be recalculated and multiplied by the coverage factor.
NOTE 1. The experience shows that with fluctuating noise, one achieves an extended uncertainty, U, of the
audibility, ΔL, of about ±1.5 dB with 12 averages.
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