Digital Audio Cables: Wire or Optical


I am trying to connect my CD/DVD player to my processor. My basic question is: Should I use the RCA digital wire interconnect or an optical cable for the audio? What is truly the difference? What is everyone experiences and/or suggestions?

Thanks
teckersley

Showing 1 response by jcbtubes

With no real attempt to clarify all of the confusion, please keep in mind that the bandwidth limitations stated are those of the "typical" transmitters/receivers usually found in consumer equipment at the time the information source was written. The optical cables are capable of far greater bandwidths with commercial grade lasers or even higher quality, current technology opto-converters. Single-mode fiber has transferred near terra-bit data rates in specialized experiments. The typical negative associated with Toslink is the poor connector pair mating. Any misalignment will result in signal loss, but also signal reflection. Toslink's plastic shells allow too much play between the connector mating. Also, multi-mode fiber is used in most Toslink cables. (Actually, I'm not aware of any Toslink using single-mode fiber, but I haven't taken a survey of all manufacturers. The Toslink shells that I'm familiar with are designed for the larger diameter multi-mode fiber.) Multi-mode uses a "reflective boundary" characteristic to propogate the signal down the fiber. This will induce additional jitter. Of course, until your equipment is completely thermally stabilized, the timing source will produce far greater levels of jitter.

Conversely, ST-type connectors typically use ceramic that is precision ground to achieve much better tip alignment. Also, single-mode fiber inherently should minimize any timing error due to the cable. However, the quality of the glass thread used in single-mode can vary. The specifications would suggest that there should be no practicle difference, but how often do we hear differences in copper cables. Just something I thought I'd toss out to further muddy the waters. In both cases, the quality of the tip polishing is very important to maximize signal transfer.

As for opto-electrical conversion time, this should be irrelevant. Jitter is the relative timing error between the leading and falling edges of the serial digital data or clock, either of a single bit or from one bit to the next. As long as the conversion time is constant, there will be no increase in jitter. Reclocking of the received data from the FIFOs is very common in digital circuitry to reduce timing errors. Extreme accuracy crystals are available, though expensive. Phase lock loops (PLL) are also routinely used to minimize clocking variations.

I guess what I'm trying to get across is that you should be careful not to be too quick to blame a particular type of cable system as much as the quality of the components used within the equipment to implement that cabling system.
Enjoy the music.