Pt. 36, App. A

A36.3.6 Recording and reproducing systems.
A36.3.6.1 A recording and reproducing system, 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 signal is retained. The recording and reproducing 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 rapidly with increasing frequency, appropriate
pre-emphasis and complementary de-emphasis networks may be included in the measurement 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 microphone 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 indicated by the readout device at any one-third
octave nominal midband frequency from 50
Hz to 10 kHz inclusive must be within Section1.5 dB
of that at the calibration check frequency.
The frequency response of a measurement
system, which includes components that
convert analog signals to digital form, must
be within Section0.3 dB of the response at 10 kHz
over the frequency range from 10 kHz to 11.2
kHz.
NOTE: Microphone extension cables as configured in the field need not be included for
the frequency response determination. This

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