IEC 61603-8-1:2003 specifies the characteristics and measuring methods for digital audio signal transmission systems using infrared radiation with sub-carrier of the frequency ranges 3 MHz to 6 MHz. It describes systems with different economic uses of the available bandwidth in order to obtain minimum interference and maximum compatibility. It replaces 6.8.3 of IEC 61603-2. This bilingual version, published in 2011-04, corresponds to the English version.