Methods for the subjective assessment of small impairments in audio systems

considering a) that Recommendations ITU-R BT.500, ITU-R BS.562, ITU-R BT.710 and ITU-R BT.811 have established some methods for assessing subjective quality of audio and video systems; b) that subjective listening tests permit assessment of the degree of annoyance caused to the listener by any impairment of the wanted signal during its transmission between the originating source and the listener; c) that classical objective methods may not be adequate in assessing advanced audio coding schemes and that perceptual objective assessment methods are being developed for testing the sound quality of sound systems; d) that the use of standardized methods is important for the exchange, compatibility and correct evaluation of the test data; e) that the introduction of new advanced digital audio systems exploiting psycho-acoustic properties, especially with small impairments requires advancements in subjective assessment methods; f) that the introduction of new multichannel stereophonic sound systems with or without accompanying picture requires new subjective assessment methods, including the experimental conditions,