Writing Quality - Page 18

Technologies for Reducing Jitter

Because of the effects of jitter can make it to your speakers, there are growing number of jitter reduction technologies of the creation of recordable CD audio discs including Yamaha's "Audio Master Quality Recording" and Plextor's "VariRec" for CD recordable discs, as well as JVC's "K2 Laser Beam Recorder" for mastering CD-ROMS.

Yamaha's Audio Master Quality Recording technology increases the window margin by lengthening the EFM marks along the track. While the actual jitter of the RF threshold crossings as measured in nanoseconds does not change, lengthening the EFM marks has the effect of lowering the relative jitter as measured as a percent of the channel clock period. The reduction of relative jitter by this technique results in a lower capacity disc (63mins vs. 74mins.), but reduces the need for activation of the error correction concealment circuitry and ultimately results in less audio distortion.

Similar EFM mark lengthening and associated relative jitter reduction can be obtained using a disc such as Kodak's 63minute Photo-CD (perhaps without also giving up recording speed, multiple sessions and "SafeBurn". There 63minute discs are made by increasing the physical length of one cycle of the wobble (the wobbled track provides the reference for spindle speed control). This lower relative wobbles frequency results in the drive spinning the disc faster which makes the marks longer.