IEC 61265 Ed. 2.0 b:2018

IEC 61265:2018 specifies requirements for the electroacoustical performance of systems of instruments used to measure sound for the purposes of aircraft noise certification, and for other comparisons among aircraft models, and provides methods by which tests can be made periodically to verify that the performance continues to conform to the requirements within stated limits.
In general, a sound measurement system for this purpose comprises a combination of instruments extending from a microphone, including its windscreen and other accessories, through data recording and processing devices to a suitable output. Different measurement systems, regardless of their composition, perform the necessary functions in different ways and operate on either analogue or digital principles.
IEC 61265:2018 cancels and replaces the first edition published in 1995. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous edition:
a) addition of guidance for measurements for aircraft other than large transport aeroplanes;
b) addition of microphones used in ground plane measurement systems;
c) addition of weighted sound level measurements other than one-third-octave band measurements, for certain aircraft types;
d) revision and clarification of requirements for digital audio recording;
e) addition of requirements for evaluation of measurement uncertainty.