Digital Audio Cables: Wire or Optical

Genesis168 wrote: "Problem exist on the receiving end of the DAC whre the optical receiver cannot cope with the bandwith and speed of the optical transmitter on the transport end causing a time delay in converting the optical signal to electrical."

Are you saying that the optical transmitter in a Toslink-based audio system is sending data too fast ("bandwidth and speed") for the receiver to process correctly? If so, do you have anything which supports this explanation?

Firstly, bandwith of TOSLINK is only 6 MHz. ST glass optical is between 50-150 MHz and electrical coax is 500 MHz.

I am not saying that the transmitter is sending the signal too fast. Rather when receiving the signal and CONVERTING it to electrical signal has a back log in doing so (takes time to do so). Transmitting will be at light speed. Receiving too at light speed but the conversion to electrical is where the problem is. Jitter is the timing error for this..we're talking micro secs to miliseconds

AT&T ST optical has far wider bandwidth therefore will better handle the signal at the receiving/conversion side.

I have read this somewhere but at this moment cannot remember where. Specs. on bandwidth is taken from "Guide to High End Audio.

Hope this helps.

In Response to Sean's comment:
Regarding additional two steps - are you saying that with coax signal starts as digital and stays digital? My impression is that it starts as digital and is then converted to some form of electrical (??) and the reverse occurs at the other end. Thus- in theory timing errors can creep into coax transmission thereby leading to jitter. And supposedly this jitter can be even MORE EXTREME than in case of toslink since the potential of RFI/EMF susceptibility of coax can be very damaging to the signal! This possibly again negates the "so called" superiority of coax over toslink. As for bandwidth, I doubt if that is even a restrictive factor. There is enough bandwidth for current signal specs.

Sean is right. Output from transport is electrical digital and stays that way until it reaches the DAC chip then converted to analog inside the chip.

If you use toslink, optical signal when input into the receiver on the DAC has to be converted to electric digital before it goes into the DAC chip hence the extra step.

On the transport side, the laser pickup DOES NOT output the optical signal. Signal from laser pickup is converted to electrical then sent to the optical LED to light up the TOSLINK cable.

Yes, coax has it's own problems with the RFI and grounding which the TOSLINK does not have.

Ultimately, it is up to you the listener to use whatever cable you think sounds better to your ears.

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.