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SPDIF cable

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SPDIF cable

Postby Michael Dow » Tue Jun 23, 2009 6:08 pm

Hi there, as far as i understand, i can use any good quality RCA cable and it will be fine? Ive got a few good ones lying around

Just got myself a little lexicon unit and want to use its digital output if i can :)

Thaanks, and i know its a pretty newbie question, i have read up a little but only from a few places im not sure i can trust as much as here!

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Re: SPDIF cable

Postby dubbmann » Tue Jun 23, 2009 6:40 pm

hi,

yes, a regular RCA cable is fine. btw, you may have to twiddle w/some params on your SPDIF rig, such as clocking. sometimes things work fine out of the box, sometimes not. good luck!

cheers,

d
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Re: SPDIF cable

Postby ramthelinefeed » Tue Jun 23, 2009 6:50 pm

dubbmann wrote:

yes, a regular RCA cable is fine.



The cable is supposed to have an impedance of 75 ohms, actually...
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Re: SPDIF cable

Postby John Willett » Tue Jun 23, 2009 7:19 pm

Michael Dow wrote:Hi there, as far as i understand, i can use any good quality RCA cable and it will be fine? Ive got a few good ones lying around

NO you can't.

The cable needs to be a 75-Ohm co-axial cable.
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Re: SPDIF cable

Postby jammy jamz » Tue Jun 23, 2009 7:35 pm

yeah, i tried it with a reg rca....it doesnt work.

S/PDIF = sony/phillips digital interface, have an orange (in north america) strip around the connector bits. its specific.

unless the rca i tried was a bad cord. but, its 30 bucks. meh.
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Re: SPDIF cable

Postby Michael Dow » Tue Jun 23, 2009 9:00 pm

ahhh
okay thanks guys maybe ill just stop being a tight arse and buy one eh!?

thaaanks yee
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Re: SPDIF cable

Postby chris... » Tue Jun 23, 2009 9:32 pm

As John W says, you should really be using 75-Ohm coax. Happily, this is normally the spec of video cable, which is cheap as chips.
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Re: SPDIF cable

Postby John Willett » Tue Jun 23, 2009 11:27 pm

Chris Edwards wrote:As John W says, you should really be using 75-Ohm coax. Happily, this is normally the spec of video cable, which is cheap as chips.

That's why it was chosen for S-PDIF. :D
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Re: SPDIF cable

Postby chris... » Wed Jun 24, 2009 12:13 am

Ah - I geddit.
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Re: SPDIF cable

Postby Hugh Robjohns » Wed Jun 24, 2009 10:39 am

75 ohms wasn't chosen as the spec because the cable was cheap. It was chosen because baseband video is a very similar signal in terms of spectrum and energy levels and it was a well proven interface standard.

Often, if the cable length is short (under a metre) you'll get away with a bog-standard audio RCA(Phono) cable and it will work.

But S/PDIF outputs and inputs aren't all designed as well as they should be and some won't cope.

Standard 75 ohm video leads with phono connectors will be absolutely fine and are very cheap. Bespoke 'digital audio' cables will also be fine, but will cost rather more and offer no tangible benefit.

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Re: SPDIF cable

Postby ramthelinefeed » Wed Jun 24, 2009 10:53 am

Hugh Robjohns wrote: Bespoke 'digital audio' cables will also be fine, but will cost rather more and offer no tangible benefit.

Yeah, but the *in*tangible benefits to the buyer's psyche are manifold :headbang:
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Re: SPDIF cable

Postby jammy jamz » Wed Jun 24, 2009 2:20 pm

oh no, the snazzy S/PDIF cable i bought for 30 CAD, has airplane braiding under the pretty plastic, with real gold connectors.

AIRPLANE BRAIDED METAL and REAL GOLD. . serious. sorta. okay not really but it does have those things.

:tongue:
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Re: SPDIF cable

Postby blinddrew » Sat Jan 18, 2020 1:24 pm

Sorry for the resurrection of a zombie thread, but there's something confusing me about all this.
What exactly is the 75 Ohm a resistance measure of?
That's terribly worded but you know what I mean I'm sure.
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Re: SPDIF cable

Postby Hugh Robjohns » Sat Jan 18, 2020 1:33 pm

It's the 'characteristic impedance' of the cable. Strictly speaking, it only applies to 'transmission lines', but the higher the frequency of the signal the shorter a cable needs to be to look like a transmission line.

A cable carrying a signal must have at least two wires, and there will therefore be the equivalent of distributed capacitance, inductance and resistance between those two wires. Those Cs, Ls and Rs collectively combine to form an impedance (frequency-dependent resistance).

The characteristic impedance is officially the impedance that would be measured at one end of an infinitely long (open-ended) cable.

So for standard video coax cable that's around 75 Ohms, RF coax will be 50 or 75 Ohms. Mic cable, AES3, and cat5/6 cables are around 100-110 Ohms, and overhead telephone cables are around 600 Ohms.
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Re: SPDIF cable

Postby blinddrew » Sat Jan 18, 2020 1:59 pm

Right.
Maybe. ;)
I shall read that again a couple of times. :)
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