This part of ISO 4412 establishes a test code describing procedures, based on ISO 2204, for the determination of the sound power levels of a hydraulic fluid power motor, under controlled conditions of installation and operation, suitable for providing a basis for comparing the noise levels of motors in terms of: — A-weighted sound power level; — octave band sound power levels. From these sound power levels, if required, reference sound pressure levels may be calculated for reporting purposes in accordance with annex A. For general purposes, the frequency range of interest includes the octave bands with centre frequencies between 125 Hz and 8 000 Hz.1) Due to the inherent difficulties in the measurement of low-speed motor performance, this part of ISO 4412 is limited to motors operating at speeds exceeding 50 r/min. Guidelines for the application of this part of ISO 4412 are given in annex C. This part of ISO 4412 is applicable to all types of hydraulic fluid power motors operating under steady-state conditions, irrespective of size, except for any limitations imposed by the size of the test environment (see clause 5).