Cable Asylum

Interconnects, speaker wire, power cords. Ask the Cable Guys.

Return to Cable Asylum

Message Sort: Post Order or Asylum Reverse Threaded

Why coaxials are good for digital and so little popular for analog signals ?

81.167.153.96
Posted on March 22, 2014 at 00:20:22
beppe61
Audiophile

Posts: 4705
Joined: January 29, 2004

Hello,
looking at the structures of analog cables i wonder why they are so complex.
Then looking at a normal good quality digital cable i usually see a quite basic coaxial structure.
Is there a reason why analog cables must be so complex ?
I understand that quality of construction and materials is of paramount importance but i really do not understand why a good coaxial should not be good enough also for analogue.
Actually i made a 3 meters IC with a generic good quality copper solid core coaxial and i liked the sound a lot.
Of course the quality of the RCAs are also important.
Thanks a lot.
Kind regards,
bg

 

Hide full thread outline!
    ...
Perhaps because the frequency spectrum of a digital signal is less important than the cable's consisent impedance?, posted on March 22, 2014 at 06:49:34
John Marks
Manufacturer

Posts: 7799
Location: Peoples' Democratic Republic of R.I.
Joined: April 23, 2000
 An SPDIF signal's information load consists of the timing of its "On-and-Off" pulses of electrical energy.

Induced reflections from impedance mismatches can blur the crispness of the starts and stops of the signals, because no physical system has infinite rise time. The SPDIF signal is not continuous; the data are encoded in the pulsing on and off of the signal. Whereas in contrast, an analog signal is continuous, and its information load consists of the frequencies and relative levels of its continuous signals.

Look at it this way: If the digital information in an SPDIF signal were being transmitted by the pulses on and off of a signal light, whether the light was on or off would be more important than the exact color of the light. That is because SPDIF is a binary signal--it has only two meaningful states; the rest is noise, which constant impedance is designed to minimize. Whereas an analog signal has hundreds of thousands of potential meaningful states-- 20 Hz to 20,000 Hz times the number of tone colors (harmonics) times the number of volume levels.

What makes coaxial good for digital--its constant impedance, because its "characteristic impedance" is the resistance between the core and shield provided by the insulation--makes it not so good for analog, because of the "skin effect," which means that within the cross-section a solid conductor, the electromagnetic flux propagates at varying speeds, with the signal tending to stay near the skin. This is believed to lead to a smearing of analog arrival times. That is the reason for Litz wire construction and construction using wires of different gauges for analog signals.

Yes, a coax cable will carry an analog signal and in some cases it will sound OK. However, once you get into the deeper end of the pool, the consensus of designers is that continuous analog music signals require special care and handling compared to the on/off of digital signals.

Years ago there was a brief vogue for using solid electrical-power wire for loudspeaker cables. One of the many audio "developments" that were, "one step forward, two steps back."

I think it is relevant to remember that coaxial cable was invented 134 years ago, for the telegraph industry, which used a DC signal--on and off. Telegraphs were a form of digital communication. And also today, coax is mostly used for radio and television frequency applications, that is, very high frequencies far removed from the audio band.

The above is all my own opinions. I do not claim to be an engineer, just a music lover with decades of on-the-job training.

I attach a link to George Cardas' historical review of cable technology, starting with open-wire telegraph systems.

JM

 

Thanks and i think i have understood, posted on March 22, 2014 at 08:13:41
beppe61
Audiophile

Posts: 4705
Joined: January 29, 2004
Hello and thanks for the valuable reply
If I understand well for a good digital signal transmission the impedance must be kept constant along the wire.
And this is relatively easy to achieve and i think maybe can even be measured.
Instead for analog signals the story is more complex with different factors influencing the signal transfer.
And no applicable measurement is available.
I hope i have understood correctly.
Thanks again,

Kind regards,
bg

 

Well stated., posted on March 22, 2014 at 17:48:02
Duster
Manufacturer

Posts: 17117
Location: Pacific Northwest
Joined: August 25, 2002



The fundamental function of a 75 ohm digital signal cable is not unlike that of a 75 ohm RF video cable. If folks keep that in mind, the difference between the requirements of a digital cable and a line-level analog cable may be better understood.

The most compelling reason to use a twisted pair or more complicated designs rather than a coaxial cable for analog applications is the ability for the cable to be unshielded, whereas a coaxial cable is shielded by nature. Many audiophiles find that shielding can do more harm than good for analog use.

However, there are coaxial cables that sound excellent when implemented as shielded analog interconnects rather than a shielded twisted pair, et al.

A new kid on the block is the new OCC copper version VH Audio Pulsar II coaxial cable for either digital or analog applications. I'm currently evaluating a stellar sounding DIY VH Audio Pulsar II OCC digital coaxial cable placed in my computer audio system. A new pair of VH Audio Pulsar II OCC analog interconnects are next in line on my DIY to-do list for potential use in my main audio system. I'll post a report sometime down the road.

 

RE: Well stated., posted on March 23, 2014 at 00:27:57
beppe61
Audiophile

Posts: 4705
Joined: January 29, 2004
 Hi and thank you very much for your always valuable advice.
You say "Many audiophiles find that shielding can do more harm than good for analog use.
However, there are coaxial cables that sound excellent when implemented as shielded analog interconnects rather than a shielded twisted pair, et al."

Could it be the case that for analog use to make the signal going through the shield is a bad design choice ?
In the sense that a shield is ok but connected just to one side for only shielding purposes
and then using the twisted wires for transfer the + and - signals ?
I wonder if the good sounding analog cables work like that.
I do not think that the shield is connected on both side
Great cable the one depicted.
Thanks again.


Kind regards,
bg

 

" Yes, a coax cable will carry an analog signal and in some cases it will sound OK ", posted on March 26, 2014 at 06:12:31
beppe61
Audiophile

Posts: 4705
Joined: January 29, 2004
 Hi and sorry it is me again.
You state " Yes, a coax cable will carry an analog signal and in some cases it will sound OK "
Could you tell me one of this cases are you aware of ?
I would really want to try a coax for analog duties. Really.
And appreciate the suggestion sincerely.
Ok for me would be more than enough.
Actually i had in the past a IC from Audioquest with a green jacket that got lost in a removal. I remeber it has a copper solid wire for + and the shield for -.
I do not remember the exact model unfortunately.
Thanks a lot indeed.
Kind regards,
bg

 

Also no one is actually making a top grade OFC coax., posted on April 3, 2014 at 12:07:44
Elizabeth
 Even Belden with ordinary wire top coax is $5 a foot due to cost of Teflon. But no one is actually making a top OFC type of coax (that I know of) All the high end OFC super OFC longgrain etc wire is ordinary wire. And plenty of it too.
Then IMO Kimber has really made a wire immune to RFI problems with their GQ weave.
Also others have no issues with RFI.
So the main reason for coax: stop RFI interference is no longer important reason to stick to coax in audio IC.

 

RE: Also no one is actually making a top grade OFC coax., posted on April 3, 2014 at 16:06:35
rick_m
Audiophile

Posts: 6230
Location: Oregon
Joined: August 11, 2005
 What was causing your RFI?

Rick

 

Let me elaborate a little, posted on April 6, 2014 at 23:04:14
beppe61
Audiophile

Posts: 4705
Joined: January 29, 2004
 First i have a great respect for good coaxials.
If they are good enough to connect probes to scope up to Ghz freq they MUST be good.
From what i have learned digital signals are more demanding than analogue ones.
Then i understand here that some coaxials are actually good also for analogue signals transfer.
My curiosity is still about what makes a coaxial good for analogue.
I have to study more i guess.
Kind regards,
bg

 

Page processed in 0.028 seconds.

[ Top Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]
[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]