simple copybit killer
simple copybit killer
The Serial CopyManagementSystem (SCMS)prevents digitalcopying of audiomaterial from thesecond generationonwards.Unfortunately, thisprotection alsoworks on homerecordings and soprevents homerecordists fromdigitally copyingtheir ownmusical work more thanonce without degradationby the SCMS. This problemhas been highlightedbefore in this magazine,but it has not gone away– reason enough todescribe a simple andinexpensive circuit forpermanently removing thecopy-prohibit-bit from theS/PDIF* audio signal.
The circuit described in this article isintended for the digital recording orcopying and playback of non-commercialmusical work. Such recordingor copying is possible only when thecopy-prohibit has been eliminatedwithout any other effect on the audiosignal.The design of the circuit is suchthat there are no modificationsrequired in the existing audio installation.The circuit is simply inserted inseries with the digital (optical or coaxial)link between the relevant recordingand playback equipment.Briefly, the circuit:• requires no modification to the digitalaudio equipment;• is suitable for use with signals onoptical as well as coaxial lines;• uses readily available components;• operates without programmableICs such as PALs and EPLDs;• is easily set up;• has good clock regenerationthrough the use of PLLs (jitterkiller);• gives clear indication (LEDs) of thesampling frequency (32 kHz,44.1 kHz, or 48 kHz);• automatically recognizes, andswitches over to, the correct samplingfrequency;• draws a small current owing to theuse of CMOS ICs.