COPYBIT INVERTER
The inverter can be included in theS/PDIF link between any digital a.f. signalsource (such as a DCC recorder, a CDplayer, a DSR receiver) and a (second) DCCrecorder without the need of opening ormodifying any of the equipment. Duringthe copying, any copybit is inverted and atthe same time the category code is altered.This means that the S/PDIF signal so modifiedis accepted by the recorder as if itcomes from a CD player (so that unlimitedcopying of the signal becomes possible).The inverter also offers a number of otherfacilities, such as S/PDIF detection.
The coding of the S/PDIF has been describedin detail in the article on the ‘Copybit eliminator’.The following description is thereforelimited to the most important aspects of it.In all domestic audio equipment, the formatuses sample frequencies of 32 kHz, 44.1kHzand 48 kHz. These data contain, among others,information as to the copybit. The format reactsto the content of the S/PDIF. The SCMS,which inhibits multiple (digital) copying of thesource signal, can be bypassed as shown inthe flow diagram in F i g . 1. It is not sufficientto invert only copybit 1. As the diagramshows, when copying with categorycode 00 000 000 (general) takes place, forinstance, the copybit is not sampled.
Thismeans that the recording has to be passedthrough a copybit eliminator a second time.It is, therefore, much safer to set the copybitto (or hold it at) 1 and assign to it the categorycode of an apparatus whose copybit isalways sampled.The present inverter always outputs thecategory code of a DAT or a CD, dependingon the input signal. The code changes automatically,so that the subdata in the USERchannel of the relevant equipment are retained.The unit can be used as a converter witheither optical or coaxial inputs and outputswithout any change in the input signal.