1. A method for determining a quality indicator representing a perceived quality of an output signal of an audio system with respect to a reference signal, where the reference signal and the output signal are processed and compared, and the processing includes dividing the reference signal and the output signal into mutually corresponding time frames, wherein the processing further comprises: scaling the intensity of the reference signal towards a fixed intensity level; performing measurements on time frames within the scaled reference signal for determining reference signal time frame characteristics; scaling the intensity of the reference signal from the fixed intensity level towards an intensity level related to the output signal; scaling the loudness of the output signal towards a fixed loudness level in the perceptual loudness domain, the output signal loudness scaling using the reference signal time frame characteristics; and scaling the loudness of the reference signal from a loudness level corresponding to the output signal related intensity level towards a loudness level related to the loudness level of the scaled output signal in the perceptual loudness domain, the reference signal loudness scaling using the reference signal time frame characteristics.