782 

14 CFR Ch. I (1–1–19 Edition) 

Pt. 36, App. A 

allowance does not eliminate the require-
ment of including microphone extension ca-
bles when performing the pink noise record-
ing in section A36.3.9.5. 

A36.3.6.4 For analog tape recordings, the 

amplitude fluctuations of a 1 kHz sinusoidal 
signal recorded within 5 dB of the level cor-
responding to the calibration sound pressure 
level must not vary by more than 

±

0.5 dB 

throughout any reel of the type of magnetic 
tape used. Conformance to this requirement 
must be demonstrated using a device that 
has time-averaging properties equivalent to 
those of the spectrum analyzer. 

A36.3.6.5 For all appropriate level ranges 

and for steady sinusoidal electrical signals 
applied to the input of the measurement sys-
tem, including all parts of the microphone 
system except the microphone, at one-third- 
octave nominal midband frequencies of 50 
Hz, 1 kHz and 10 kHz, and the calibration 
check frequency, if it is not one of these fre-
quencies, the level non-linearity must not 
exceed 

±

0.5 dB for a linear operating range of 

at least 50 dB below the upper boundary of 
the level range. 

N

OTE

1: Level linearity of measurement 

system components may be tested according 
to the methods described in IEC 61265 as 
amended. 

N

OTE

2: Microphone extension cables con-

figured in the field need not be included for 
the level linearity determination. 

A36.3.6.6 On the reference level range, the 

level corresonding to the calibration sound 
pressure level must be at least 5 dB, but no 
more than 30 dB less than the upper bound-
ary of the level range. 

A36.3.6.7 The linear operating ranges on ad-

jacent level ranges must overlap by at least 
50 dB minus the change in attenuation intro-
duced by a change in the level range con-
trols. 

N

OTE

: It is possible for a measurement sys-

tem to have level range controls that permit 
attenuation changes of either 10 dB or 1 dB, 
for example. With 10 dB steps, the minimum 
overlap required would be 40 dB, and with 1 
dB steps the minimum overlap would be 49 
dB. 

A36.3.6.8 An overload indicator must be in-

cluded in the recording and reproducing sys-
tems so that an overload indication will 
occur during an overload condition on any 
relevant level range. 

A36.3.6.9 Attenuators included in the meas-

urement system to permit range changes 
must operate in known intervals of decibel 
steps. 

A36.3.7 

Analysis systems. 

A36.3.7.1 The analysis system must con-

form to the specifications in sections 
A36.3.7.2 to A36.3.7.7 for the frequency 
bandwidths, channel configurations and gain 
settings used for analysis. 

A36.3.7.2 The output of the analysis system 

must consist of one-third octave band sound 
pressure levels as a function of time, ob-
tained by processing the noise signals (pref-
erably recorded) through an analysis system 
with the following characteristics: 

(a) A set of 24 one-third octave band filters, 

or their equivalent, having nominal midband 
frequencies from 50 Hz to 10 kHz inclusive; 

(b) Response and averaging properties in 

which, in principle, the output from any one- 
third octave filter band is squared, averaged 
and displayed or stored as time-averaged 
sound pressure levels; 

(c) The interval between successive sound 

pressure level samples must be 500 ms 

±

5 mil-

liseconds(ms) for spectral analysis with or 
without slow time-weighting, as defined in 
section A36.3.7.4; 

(d) For those analysis systems that do not 

process the sound pressure signals during the 
period of time required for readout and/or re-
setting of the analyzer, the loss of data must 
not exceed a duration of 5 ms; and 

(e) The analysis system must operate in 

real time from 50 Hz through at least 12 kHz 
inclusive. This requirement applies to all op-
erating channels of a multi-channel spectral 
analysis system. 

A36.3.7.3 The minimum standard for the 

one-third octave band analysis system is the 
class 2 electrical performance requirements 
of IEC 61260 as amended, over the range of 
one-third octave nominal midband fre-
quencies from 50 Hz through 10 kHz inclusive 
(incorporated by reference, see § 36.6). 

N

OTE

: IEC 61260 specifies procedures for 

testing of one-third octave band analysis 
systems for relative attenuation, anti- 
aliasing filters, real time operation, level 
linearity, and filter integrated response (ef-
fective bandwidth). 

A36.3.7.4 When slow time averaging is per-

formed in the analyzer, the response of the 
one-third octave band analysis system to a 
sudden onset or interruption of a constant 
sinusoidal signal at the respective one-third 
octave nominal midband frequency, must be 
measured at sampling instants 0.5, 1, 1.5 and 
2 seconds(s) after the onset and 0.5 and 1s 
after interruption. The rising response must 
be 

¥

4 

±

1 dB at 0.5s, 

¥

1.75 

±

0.75 dB at 1s, 

¥

1 

±

0.5 dB at 1.5s and 

¥

0.5 

±

0.5 dB at 2s relative 

to the steady-state level. The falling re-
sponse must be such that the sum of the out-
put signal levels, relative to the initial 
steady-state level, and the corresponding ris-
ing response reading is 

¥

6.5 

±

1 dB, at both 0.5 

and 1s. At subsequent times the sum of the 
rising and falling responses must be 

¥

7.5 dB 

or less. This equates to an exponential aver-
aging process (slow time-weighting) with a 
nominal 1s time constant (

i.e., 

2s averaging 

time). 

A36.3.7.5 When the one-third octave band 

sound pressure levels are determined from 

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