digital cables

[dallas100]

I understand that the better the quality an analog cable produces the better the sound and/or video you can receive but I don't understand why digital cables have the same effect. Correct me if I am wrong if the data that travels throught the digital cables is either 0 or 1 why would that cable effect the quality of the 0 or 1 that it trasmits. I am just ignorant to why a digital cable whether it has gold terminals or some other special something would have some greated effect on quality. For comparison you can get video cards for a computer can cost as much as the computer itself but I don't see any higher quality vga or dvi cables in the computer sections of your average electronics superstore. A good explanation would be very much warranted.


Dallas100

 

[markw]

I tend to agree with you on the digital issue that a lot pf puffery is employed..

I do, however, question your facts on the "better quality" able producing the better sound in analog. All things being equal, the differences in cables are highly exaggerated.

There's more puffery in the "audiophile" cable industry than anywhere else in the audio hobby. Why? ...simply because "better" is purely subjective and cannot be proved via scientific methods. It depends on belief and faith.

 

[MDS]

In a very basic sense, digital signals consist of zeros and ones but that is a vast oversimplification. How do you send a 0 or a 1 over a cable?

A better constructed cable, whether coaxial or optical, will be more immune to the little things that can cause data errors but all the talk of fancy gold plated connectors and the like don't affect the signal at all - especially over the very short distances most cables will run in a typical HT system.

I can explain it in layman's terms if you really want to know...(most don't )

 

[dallas100]

thanks for the replies


Actually MDS if you could explain it better or link to some unbiased explanation i would much appreciate it.

 

[BMXTRIX]

I don't know if you will ever find unbiased opinions, but I can tell you that I've run digital coaxial 3 feet over one of Monsters better digital coaxial cables and I've run it over a 40 foot piece of mini-RG59 cable that I terminated myself...

Can't say I heard any difference whatsoever.

THAT is what I believe matters. If nobody can hear the difference, then there is no difference. Doesn't matter if there is or isn't a difference there at some sub-audible level. I don't care. I care about what I can hear.

 

[MDS]

Sending digital information over a wire requires a 'modulation' scheme; ie a way to represent a zero or one.

Electrical
NRZ (Non Return to Zero) is the most common modulation scheme and is what is used for S/PDIF. One voltage represents a one and another lower voltage represents a zero [positive logic NRZ]. There are no intermediate values, which is why it is called non-return to zero.

So if +5 volts is a one and +2 volts is a zero, then to send 101, a 'pulse' of +5 volts is followed by a pulse of +2 volts is followed by a pulse of +5 volts. The 'pulse' is how long that voltage level persists.

If the cable is damaged or is affected by rfi/emi interference (ie 'poorly constructed') then it may interfere with the levels and/or timing seen by the receiving device. For example, if the device sees a voltage of +3 volts, should it interpret it as 1 with too low a voltage or as a zero with too high a voltage?

Optical
Optical is far easier to explain with an analogy. If the sender and receiver agree that a zero is a .5 second pulse of light and a one is a 1 second pulse of light, then all you have to do to ensure the message is received correctly is to make sure your pulses are exactly .5 seconds or 1 second long (with an agreed upon time between each 'bit' so the receiver can distinguish when one ends and another begins). [The pulses are far shorter than that for digital audio].

The pulses of light travel down the cable because of the principle of 'total internal reflection'. If the cable is bent severely or is made poorly and some of the light escapes the tunnel it is travelling down, it won't propagate down the tunnel with the correct timing. So again, if the receiving devices thinks it sees a pulse that is .75 seconds long, was that meant to be a zero but the pulse was too long or was it meant to be a one and the pulse was too short?


So cables CAN affect the transmission of digital audio but generally only if they are broken or really poorly made. Small errors can often be corrected but over the short distances and fairly low bitrate of audio, errors are practically nonexistent.

 

[markw]

Don't forget...

With optical there are at least two more stages of conversion the signal needs to pass through. First, the conversion from electrival to optical at the source and then the conversion from optical (back) to electrical at the target.

Kinda flies in the face of logic, doesn't it?

 

[jaxvon]

But remember that's not D/A conversion, it's D/D. It's just pulses of electricity going to an LED for the first "conversion".

 

[markw]

and???

But remember that's not D/A conversion, it's D/D. It's just pulses of electricity going to an LED for the first "conversion".

This is any better??? Look at like electricity being converted to sound waves via a loudspeaker, being passed through air and then being reconverted to electricity via a microphone.

 

[Hi Ho]

I have a 50 foot length of RG-6 cable that I terminated mysefl running under my house from the PC to the theater system. It cost me about $10 in parts to make and it works great. It sounds much better than the analog signal I used to have running through it + plus another cable.

 

[Buckle-meister]

Sending digital information over a wire requires a 'modulation' scheme; ie a way to represent a zero or one.

Electrical

Optical

I wont quote all of it due to its length, but thanks for this; I think it's an excellent piece of text. It's this kind of material that I really enjoy reading here.

Regards