Using audio cable as digital coax?

Discussion in 'Archived Threads 2001-2004' started by Jason Wilcox, Mar 17, 2002.

  1. Jason Wilcox

    Jason Wilcox Supporting Actor

    Joined:
    Feb 21, 2002
    Messages:
    652
    Likes Received:
    0
    I had an extra set of AR performance series audio cables so I pulled the two wires apart and I use one for my sub and one for digital coax from my dvd player to my receiver. It sounds great to me, but am I missing out on good sound using these cables and not the AR digital coax or composite video which are said to be 75 ohms. the audio cables lack an ohms rating. the only visible difference between the cables is that the digital coax and composite video cables are thicker than my audio cables. Becuase the music and movies sound great through my audio cable used as a digital coax cable, does that mean it is in fact 75 ohms?
     
  2. BruceD

    BruceD Screenwriter

    Joined:
    Apr 12, 1999
    Messages:
    1,220
    Likes Received:
    0
    Typically most analog audio cables (including the RCA connectors) are rated as 50 Ohm cables. This is not what you want to use for a digital coax cable. What will it do to the sound? I'm not sure, maybe attenuate highs.

    You can use a video cable with RCA connectors which is a 75 Ohm cable with good results for a digital coax cable, in fact they are the same thing, just different labels.
     
  3. Jason Wilcox

    Jason Wilcox Supporting Actor

    Joined:
    Feb 21, 2002
    Messages:
    652
    Likes Received:
    0
    ok thanks, i'll pick up some AR digital coax tommorow (it's very cheap with my employee discount)

    what about for the sub? do you need 75ohm cable?
     
  4. Brian Fellmeth

    Brian Fellmeth Supporting Actor

    Joined:
    Jul 30, 2000
    Messages:
    789
    Likes Received:
    0
    Either one works fine for subs
     
  5. Brad Craig

    Brad Craig Stunt Coordinator

    Joined:
    Feb 1, 2002
    Messages:
    58
    Likes Received:
    0
    I was thinking digital coax had a bigger prong on the RCA end than a regular RCA prong...

    Guess not???

    Also I heard that the digital coax is double shielded whereas a normal RCA video cable is not

    Is that right or wrong???
     
  6. Allan Jayne

    Allan Jayne Cinematographer

    Joined:
    Nov 1, 1998
    Messages:
    2,404
    Likes Received:
    0
    If it works for digital coax, it is probably fine. A short length of audio cable probably won't cause degradation, in fact it might coincidentally be 75 ohm (could vary from one manufacturing batch to another of the same make and model).
    For digital signals, slight degradation due to a bad cable will be very noticeable in the results.
    Video hints:
    http://members.aol.com/ajaynejr/video.htm
     
  7. Brad Craig

    Brad Craig Stunt Coordinator

    Joined:
    Feb 1, 2002
    Messages:
    58
    Likes Received:
    0
    Can someone answer my question above >>> thanks
     
  8. Brian Fellmeth

    Brian Fellmeth Supporting Actor

    Joined:
    Jul 30, 2000
    Messages:
    789
    Likes Received:
    0
    1) the connectors are the same

    2) The spec for digital coax is the same as a RCA video cable. There really is no such thing as a dedicated digital specific cable. It just needs to be a cable capable of handeling high frequency signals, which a video cable is. Sub cables do not carry high any frequency information, so the demands of that application is less and RCA audio cable is good enough. "double shielding" and "digital cable" are marketing terms, not defined technical specifications.
     
  9. Jacques C

    Jacques C Stunt Coordinator

    Joined:
    Nov 28, 2001
    Messages:
    84
    Likes Received:
    0
    The sub cable needs to be better shielded, so a good 75 ohm coax is in order (those runs tend to be longer anyway).

    For the digital, a coat hanger will do (i.e. anything). And yes, a coat hanger has been tried and was bit-for-bit perfect. ;-)
     
  10. Philip Hamm

    Philip Hamm Lead Actor

    Joined:
    Jan 23, 1999
    Messages:
    6,873
    Likes Received:
    2
    I wouldn't say that anything would work. [​IMG] The coat hanger test was performed on Dolby Digital with a lower bitrate than conventional PCM has. I would try the audio cable, and if you get dropouts and problems then try a video cable. I use megacheap cables and have no complaints. I have however, experienced dropouts using inadequate cables.
     
  11. Jason Wilcox

    Jason Wilcox Supporting Actor

    Joined:
    Feb 21, 2002
    Messages:
    652
    Likes Received:
    0
    now i'm confused by this whole ohms thing...so a 75 ohm cable offers 75 ohms of resistance to the flow of electricity.....isn't that a lot for a copper cable?....are there 75 ohm resistors in the connectors of these RCA cables because i don't understand how the cable itself can have this much resistance
     
  12. Bob McElfresh

    Bob McElfresh Producer

    Joined:
    May 22, 1999
    Messages:
    5,182
    Likes Received:
    0
    Jason: it isconfusing.
    Resistance is for DC, but for a changing signal, there is another kind of resistance called "Impedence".
    Basically as the signal suddenly goes from nothing to something, a magnetic field is built up around the wire. This takes some energy. Since it acts like resistance, this loss is measured in ohms.
    Each time the frequency of the signal changes - the magnetic field changes so some energy is lost.
    So coax can be thought of as having aproximatly 75 ohms of resistance to an AC signal.
    Note: This is a "model" for you to keep in mind. I am glossing over a lot of stuff so the rest of the class should not bother to tell me how much I skipped. [​IMG]
    Does this help?
     
  13. BruceD

    BruceD Screenwriter

    Joined:
    Apr 12, 1999
    Messages:
    1,220
    Likes Received:
    0
    My modus operandi is to simply buy and use AV cables (75 Ohm) for all interconnects between digital, video and analog audio components.
    This way I will never accidently connect a 50 Ohm cable to a device that needs a 75 Ohm cable.
     
  14. Jeff Kleist

    Jeff Kleist Executive Producer

    Joined:
    Dec 4, 1999
    Messages:
    11,267
    Likes Received:
    0
    Bottom line, any RCA cable will work for both

    With a digital signal, it's all or nothing, and I use a cheap-ass cable for my digital coax and I'm going strong
     
  15. Bill Lucas

    Bill Lucas Supporting Actor

    Joined:
    Mar 20, 1999
    Messages:
    530
    Likes Received:
    0
    "With a digital signal, it's all or nothing"

    Wrong! I suppose that there's no difference between a boombox and high-end gear either.
     
  16. Jason Wilcox

    Jason Wilcox Supporting Actor

    Joined:
    Feb 21, 2002
    Messages:
    652
    Likes Received:
    0
    well it is just ones and zeros...so logic would lead many to beleive that hey, my computer cables aren't gold plated and oxygen free with multiple layers of shielding, and they work fine!......but, computers use data correction when sending data....so if the data that was supposed to be there isn't....the signal (or packet or whatever) is sent again....the reason there can be data correction is that in most applications delay isn't a problem.....(this is why voice transmission is on a different frequency than data)......this is also why data correction is not used in home audio....it would be kind of annoying if the action on your tv didn't synch up with the sound becuase the signal had to be rebroadcasted to your receiver.....SO, if you use a very poor quality cable, you may be missing out on a lot of audio becuase instead of sending the data again....it's just lost and forgotten [​IMG]
     
  17. Bob McElfresh

    Bob McElfresh Producer

    Joined:
    May 22, 1999
    Messages:
    5,182
    Likes Received:
    0
     
  18. Jason Wilcox

    Jason Wilcox Supporting Actor

    Joined:
    Feb 21, 2002
    Messages:
    652
    Likes Received:
    0
    i'm just gonna buy a digital coax cable and use my present digital coax/audio cable for my sub. can i use a video RCA coupler with audio cables?
     
  19. Mike H Wizard

    Mike H Wizard Stunt Coordinator

    Joined:
    Mar 7, 2002
    Messages:
    55
    Likes Received:
    0
    My 2 cents worth of information,

    On my HT I used the 6 foot Acoustic Research "Video" Cable I bought from Best Buy for like $12.00...

    I used that AR "Video" cable for my digital coax for the Audio from my DVD Player to my Receiver and I think it works great!

    Hope this Helps...
     

Share This Page