923 

Federal Aviation Administration, DOT 

Pt. 36, App. A 

differences at sound incidence angles be-
tween any two adjacent sound incidence an-

gles in Table A36–1 must not exceed the tol-
erance limit for the greater angle. 

A36.3.6 

Recording and reproducing systems. 

A36.3.6.1 A recording and reproducing sys-

tem, such as a digital or analog magnetic 
tape recorder, a computer-based system or 
other permanent data storage device, must 
be used to store sound pressure signals for 
subsequent analysis. The sound produced by 
the aircraft must be recorded in such a way 
that a record of the complete acoustical sig-
nal is retained. The recording and reproduc-
ing systems must meet the specifications in 
sections A36.3.6.2 to A36.3.6.9 at the recording 
speeds and/or data sampling rates used for 
the noise certification tests. Conformance 
must be demonstrated for the frequency 
bandwidths and recording channels selected 
for the tests. 

A36.3.6.2 The recording and reproducing 

systems must be calibrated as described in 
section A36.3.9. 

(a) For aircraft noise signals for which the 

high frequency spectral levels decrease rap-

idly with increasing frequency, appropriate 
pre-emphasis and complementary de-empha-
sis networks may be included in the meas-
urement system. If pre-emphasis is included, 
over the range of nominal one-third octave 
midband frequencies from 800 Hz to 10 kHz 
inclusive, the electrical gain provided by the 
pre-emphasis network must not exceed 20 dB 
relative to the gain at 800 Hz. 

A36.3.6.3 For steady sinusoidal electrical 

signals applied to the input of the entire 
measurement system including all parts of 
the microphone system except the micro-
phone at a selected signal level within 5 dB 
of that corresponding to the calibration 
sound pressure level on the reference level 
range, the time-average signal level indi-
cated by the readout device at any one-third 
octave nominal midband frequency from 50 
Hz to 10 kHz inclusive must be within 

±

1.5 dB 

of that at the calibration check frequency. 
The frequency response of a measurement 

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