clipping indicator for compact disc
A little while ago areader wrote to saythat he had foundoverdrive on some ofhis compact discs.This sort of newscomes of course likea thunderbolt since itis assumed by mostpeople that compactdiscs are examples ofthe quality of today’sdigital technology.The first reaction tosuch an allegation isone of outright disbeliefor at least scepticism.Moreover, it hasbeen alleged by otherreaders that severalproducers haveadmitted (sic!) tooverdriving, that isclipping, of CDs atthe request of the relevantartists. Be thatas it may, it was reasonenough to designan indicator to bringoverdrive to light andhelp the consumer inhis/her quest not tobuy flawed CDs.
Most people will not believe that thereare CDs that are overdriven by theproducer: they generally assume thatmanufacturers know what they aredoing and supply discs that are technicallycorrect within the confines ofmodern digital technology. If the experiencesof some of our readers areaccepted, this may not always be true.One reader wrote to say that hehad noticed that some CDs in his collectionsounded ‘less than perfect’ andothers even ‘downright poor’. Since hethought that his ears were playing himtricks, he decided to check the levelwith a VU (visual unit). To his surprisehe found that the level varied around0 dB. A surprise, indeed, for the levelon a CD should reach 0 dB only duringvery brief peaks in the signal. Theaverage signal strength should be notless than 6 dB and preferably 10–12 dBbelow 0 dB.