Specifies requirements for the electroacoustical performance of systems of instruments used to measure sound for the purposes of aeroplane noise certification, and recommends methods by which tests may be made periodically to verify that the performance continues to comply with the requirements given within stated tolerances. The sound measurement system herein comprises a combination of instruments extending from a microphone through data recording and processing devices to a suitable output. Ensures that different measurement systems have the same electroacoustical characteristics within the stated tolerances under specified reference environmental conditions. Does not provide recommendations for installation of microphones or microphone windscreens, nor requirements for measurement and analysis procedures used in aeroplane noise certification.