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.
s(i,k) = SPL(i,k) - SPL(i-1,k)
Step 2. Encircle the value of the slope, s(i,k), where the
absolute value of the change in slope is greater than five; that
is, where:
Step 3.
a) If the encircled value of the slope s(i,k) is positive and
algebraically greater than the slope s(i-l,k), encircle
SPL(i. k).
b) If the encircled value of the slope s(i,k) is zero or
negative and the slope s(i-1,k) is positive, encircle
SPL(i-1,k).
c) For all other cases, no sound pressure level value is to
be encircled.
Step 4. Compute new adjusted sound pressure levels,
SPL1(ik, ), as follows:
a) For non-encircled sound pressure levels, let the new
sound pressure levels equal the original sound pressure
levels, SPL1(ik, ) = SPL(i,k).
b) For encircled sound pressure levels in bands 1 to 23
inclusive, let the new sound pressure level equal the
arithmetic average of the preceding and following sound
pressure levels:
c) If the sound pressure level in the highest frequency band
(i = 24) is encircled, let the new sound pressure level in
that band equal:
Step 5. Recompute new slopes st(i,k), including one for an
imaginary 25th band, as follows:
Step 6. For i from 3 to 23 (or 1 to 23 for helicopters),
compute the arithmetic average of the three adjacent slopes as
follows:
Step 7. Compute final one-third octave-band sound
pressure levels, SPL"(i,k), by beginning with band number 3
(or band number 1 for helicopters) and proceeding to band
number 24 as follows:
24/11/05 APP 2-10
Appendix 2 Annex I6 - Environmental Protection
Step 8. Calculate the differences, F(i,k), between the
original sound pressure level and the final broadband sound
pressure level as follows:
F(i, k) = SPL(i, k) - SPL" (i, k)
and note only values equal to or greater than one and a half.
Steu 9. For each of the relevant one-third octave bands (3 to
24), determine tone correction factors from the sound pressure
level differences, F(i,k), and Table A2-2.
Step 10. Designate the largest of the tone correction factors,
determined in Step 9, as C(k). An example of the tone
correction procedure is given in Table A4-2 of Appendix 4 of
Doc 9501.
Tone corrected perceived noise levels PNLT(k) shall be
determined by adding the C(k) values to corresponding PNL(k)
values, that is:
For any i-th one-third octave band, at any k-th increment of
time, for which the tone correction factor is suspected to'result
from something other than (or in addition to) an actual tone (or
any spectral irregularity other than aircraft noise), an additional
analysis may be made using a filter with a bandwidth
narrower than one-third of an octave. If the narrow band analysis
corroborates these suspicions, then a revised value for the
broadband sound pressure level, SPL1(i,k), shall be determined
from the narrow band analysis and used lo compute a revised
tone correction factor for that particular one-third octave band.
Note.- Other methods of rejecting spurious tone corrections
such as those described in Appendix 2 of Doc 9501 may
be used.
4.3.2 This procedure will underestimate EPNL if an
important tone is of a frequency such that it is recorded in two
adjacent one-third octave bands. It shall be demonstrated to the
satisfaction of the certificating authority:
either that this has not occurred,
or that if it has occurred that the tone correction has been
adjusted to the value it would have had if the tone had
been recorded fully in a single one-third octave band.
Table A2-2. Tone correction factors
0 5 10 15 20 25
Level difference F, dB
Frequency Level difference Tone correction
f, Hz F, dB C, dB
* See Step 8 of 4.3.1.
APP 2-1 1
Annex I6 - Environmental Protection Volume I
4.4 Maximum tone corrected
perceived noise level
4.4.1 The maximum tone corrected perceived noise
level, PNLTM, shall be the maximum calculated value of the
tone corrected perceived noise level PNLT(k). It shall be
calculated in accordance with the procedure of 4.3. To obtain
a satisfactory noise time history, measurements shall be made
at 500 ms time intervals.
Note 1.- Figure A2-2 is an example of aflyover noise time
histoly where the maximum value is clearly indicated.
Note 2 .In the absence of a tone correctionf actol; PNLTM
would equal PNLM
4.4.2 After the value of PNLTM is obtained, the frequency
band for the largest tone correction factor is identified for the
two preceding and two succeeding 500 ms data samples. This
is performed in order to identify the possibility of tone
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