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spectrum to account for the subjective response to the
presence of spectral irregularities;
c) the tone correction factor is added to the perceived noise
level to obtain tone corrected perceived noise levels,
PNLT(k), at each one-half second increment of time:
The instantaneous values of tone corrected perceived
noise level are derived and the maximum value,
PNLTM, is determined;
d) a duration correction factor, D, is computed by integration
under the curve of tone corrected perceived noise
level versus time;
e) effective perceived noise level, EPNL, is determined by
the algebraic sum of the maximum tone corrected perceived
noise level and the duration correction factor:
6. See Table A 1-1. EPNL = PNLTM + D.
Total perceived noisiness, N, noys
Figure Al-1. Perceived noise level as a function of total perceived noisiness
APP 1-7
Anna 16 - Environmental Protection Volume I
4.2 Perceived noise level
Instantaneous perceived noise levels, PNL(k), shall be calculated
from instantaneous one-third octave band sound pressure
levels, SPL(i,k), as follows:
Step I . Convert each one-third octave band, SPL(i,k), from
50 to 10 000 Hz, to perceived noisiness, n(i,k), by reference
to Table Al-1, or to the mathematical formulation of the noy
table given in Section 7.
Step 2. Combine the perceived noisiness values, n(i,k),
found in Step 1 by the following formula:
where n(k) is the largest of the 24 values of n(i,k), and N(k) is
the total perceived noisiness.
Step 3. Convert the total perceived noisiness, N(k), into perceived
noise level, PNL(k), by the following formula:
10
PNL(k) = 40.0 + - log 2 log N(k)
which is plotted in Figure Al-1. PNL(k) may also be obtained
by choosing N(k) in the 1 000 Hz column of Table Al-1 and
then reading the corresponding value of SPL(i,k) which, at
1 000 Hz, equals PNL(k).
4.3 Correction for spectral
irregularities
Noise having pronounced spectral irrcgularitics (for cxample,
the maximum discrete frequency components or tones) shall
be adjusted by the correction factor, C(k), calculated as
follows:
Step I . Starting with the corrected sound pressure level in
the 80 Hz one-third octave band (band number 3), calculate
the changes in sound pressure level (or "slopes") in the
remainder of the one-third octave bands as follows:
s(3,k) = no value
~(4,k)= SPu4,k) - SPL(3,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:
1 A s (i,k) ( = ( s (i,k) - s [(i - l), k] ( >5
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-l),k] is positive, encircIe
SPL[(i-l),k].
c) For all other cases, no sound pressure level value is to
be encircled.
Step 4. Omit all SPL(i,k) encircled in Step 3 and compute
new adjusted sound pressure levels, SPL1(i,k), as follows:
a) For non-encircled sound pressure levels, let the new
sound pressure levels equal the original sound pressure
levels, SPL1(i, k) = SPL(i, k).
Table Al-2. Tone correction factors
0 5 10 15 20 25
Level difference F, dB
Level Tone
Frequency difference correction
3, Hz F, C, dB
* See Step 8 of 4.3.
APP 1-8
Appendix 1 Annex 16 - Environmental Protection
b) For encircled sound pressure levels in bands 1 to 23 Step 10. Designate the largest of the tone correction
inclusive, let the new sound pressure level equal the factors, determined in Step 9, as C(k). An example of the
arithmetic average of the preceding and following sound tone correction procedure is given in Table A1-3.
pressure levels:
Tone corrected perceived noise levels PNLT(k) shall be
SPL1(i, k) = (112) ( SPL[(i-l),k] + SPL[(i+l),k] } determined by adding the C(k) values to corresponding
PNLT(k) values, that is:
c) If the sound pressure level in the highest frequency band
(i = 24) is encircled, let the new sohd level in
that band equal:
Step 5. Recompute new slopes sl(i,k), including one for an
imaginary 25th band, as follows:
Stq 6. For i eom 3 to 23, compute the arithmetic average
of the three adjacent slopes as follows:
Step 7. Compute final one-third octave-band background
sound pressure levels, SPLW(i,k)b,y beginning with band number
3 and proceeding to band number 24 as follows:
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
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