RCA analog and digital difference

[Wookson]

I have question regarding rca cables.

I see they sell rca analog and rca digital cables.
What is the difference between them?

Most of the rca cables dont mention digital or analog...

What do i need to connect my avr (marantz cinema 60) to my amp (emotiva basx3+)?

 

[voodooless]

“digital” RCA cables are generally coaxial, matched for SPDIF over coax.

The “analog” ones can be anything…

For your use case, either will work. Just get the one that you find looks acceptable, has a reasonable price, and is of the correct length.

 

[DVDdoug]

With a short cable, usually there is no difference. If you have a cable that works it's usually "perfect". If the digital data gets corrupted you'll usually get silence or pure noise.

Digital (and video) has higher frequencies and with longer lengths the cable impedance needs to be matched (75 Ohms).

If you already have a cable that works don't go-out and buy a digital cable but if you need to buy one, get one rated for digital. Or buy whatever's cheaper and try it first.

The digital cable may have a different color code than the usual white/black for right/left. Sometimes the color of the connector is the ONLY difference. And, the "digital" cable may be priced a bit higher than an identical "analog" cable.

At audio frequencies the cable doesn't have an "impedance". It has a very-low resistance and some small capacitance, both proportional to length and both insignificant with line-level audio. Line-level outputs are low-impedance (usually 1K Ohm or less) and line-inputs are high-impedance (usually 10K or more) so they are not "matched"

 

[Ropeburn]

Fun fact: it's the same with MIDI cables (5-pin DIN plugs or in newer times 3.5mm TRS). Electrically it's based on the UART/RS232 standard and the requirements are low enough, you can use any audio cable and it'll work.

 

[LTig]

I have question regarding rca cables.

I see they sell rca analog and rca digital cables.
What is the difference between them?

Digital cables have a cable impedance of 75 Ohm and are meant to be used for SPDIF connections. You can also use them for analog connections. A simple cheap satellite TV cable with RCA connectors is sufficient.

Analog cables are meant for analog connections. They may also work for SPDIF connections - actually most do when the cable is short (less than 2m); just try it, if the sound is neither interrupted nore noisy it's fine.

Most of the rca cables dont mention digital or analog...

Those are analog cables.

What do i need to connect my avr (marantz cinema 60) to my amp (emotiva basx3+)?

As this is an analog connection: any cable will do.

 

[egellings]

I have question regarding rca cables.

I see they sell rca analog and rca digital cables.
What is the difference between them?

Most of the rca cables dont mention digital or analog...

What do i need to connect my avr (marantz cinema 60) to my amp (emotiva basx3+)?

The digital cables have a defined characteristic impedance assigned to them since digital signals are high frequency in nature (very short rise & fall time pulse edges especially), and reflections of the signal in the cable are possible. The wavelength of the digital signal is smaller than the cable's length, allowing for the signal to be reflected back & forth in an improperly terminated cable. By defining the impedance, often 75 ohms, and terminating both ends with that impedance, that is, the source has a 75 ohm source impedance and the receiving end is terminated in the same impedance, the reflections will be eliminated. The physical dimensions of the cable's conductors and to a lesser degree internal insulation determine the characteristic impedance. Connectors used in that setting also need to be designed to work with the cable's characteristic impedance as well. In the case of the analog audio cable, the upper frequency is so low 20kHz or so, (I can jump up and down with a beer in my hand at that rate!) that the wavelength is far longer than the cable is, so the voltage will be nearly identical at both ends of the cable at all times, since the signal is too long to bounce back & forth in such a cable. There are no reflections to speak of in an analog audio cable and therefore no termination resistance is needed to dissipate them. A cable intended for digital speed signals will work in an analog audio setting, but the analog cable won't fare well with digital signals, unless by chance, it happens to have the correct characteristic impedance, which is highly unlikely. As the RF guys say, at 20kHz, we just get out and walk!

 

[DVDdoug]

A quick internet search confirms my suspicion that RCA connectors are not proper 75 Ohm RF connectors. But obviously they are close-enough for the relatively-lower frequencies used for composite video or digital audio.

 

[egellings]

A quick internet search confirms my suspicion that RCA connectors are not proper 75 Ohm RF connectors. But obviously they are close-enough for the relatively-lower frequencies used for composite video or digital audio.

They sorta work.

 

[mhardy6647]

They sorta work.

The mantra of an engineer (i.e., close enough).
And I mean that neither facetiously nor in a denigrating manner.

 

[egellings]

Agree. Engineering something more elaborate than the application requires is not good engineering practice, since a bunch of extra cost & complexity that does not help achieve the goal gets incurred. Git 'er done and then get out.

 

[tmtomh]

I too have used a mix of "digital" and "analogue" RCA cables for short digital connections (about 6 feet or less) and never had an issue.

When I first got my current gear, which requires an SPDIF (coax/RCA) to AES EBU converter cable, I bought a $35 "digital" cable spec'd at 110 ohm for the purpose, and an $8 or $9 Monoprice cable sold as an analogue RCA-to-XLR converter and only spec'd at 75 ohm. The Monoprice cable was 1 foot longer (6 vs 5 ft) which made it lay a bit better in my application, and it was more inconspicuous looking (black vs a bright blue for the digital one). So I tried it first, and it worked perfectly. It's remained in my signal chain ever since, for the last 2+ years. Never had a single problem with it.

 

[Ropeburn]

A quick internet search confirms my suspicion that RCA connectors are not proper 75 Ohm RF connectors. But obviously they are close-enough for the relatively-lower frequencies used for composite video or digital audio.

Now I'm curious: what exactly is a "75 Ohm connector"? Or a "110 Ohm connector" in case of AES/EBU cables?

This is not just semantics. We're supposed to be precise and scientific, that's the whole point of this forum.

From all I know, the connector type has precisely NOTHING to do with the type of application any cable is intended for.

 

[voodooless]

From all I know, the connector type has precisely NOTHING to do with the type of application any cable is intended for.

It does for RF! Typically you’d use a BNC connector if you want proper impedance matching. Other smaller connectors are available for other RF stuff, like SMA, etc.

 

[Ropeburn]

The mantra of an engineer (i.e., close enough).
And I mean that neither facetiously nor in a denigrating manner.

Close enough.

 

[Ropeburn]

It does for RF! Typically you’d use a BNC connector if you want proper impedance matching. Other smaller connectors are available for other RF stuff, like SMA, etc.

Hm. Then what is the physical difference between BNC and RCA for example, beyond convention and one of them locking? Both are coaxial and two-pole.

 

[JustJones]

What do i need to connect my avr (marantz cinema 60) to my amp (emotiva basx3+)?

Looks like you would need 3 RCA cables if you're using all 3 channels of the amplifier. Either analog or digital would work.

 

[sergeauckland]

Hm. Then what is the physical difference between BNC and RCA for example, beyond convention and one of them locking? Both are coaxial and two-pole.

The inner and outer diameters and insulation materials of a BNC are closely controlled to provide a 75 ohm impedance. There are also 50 ohm BNCs used in RF work. The two will sort of interconnect, but it's considered bad practice. Unfortunately they look much the same although there are differences if you know what to look for.

I once worked in a video facility where it was a sacking offence to bring a 50 ohm BNC onto the premises!

RCA plugs and sockets have no particular impedance although as digital audio isn't very critical, they all pretty much work.

S

 

[antcollinet]

The inner and outer diameters and insulation materials of a BNC are closely controlled to provide a 75 ohm impedance. There are also 50 ohm BNCs used in RF work. The two will sort of interconnect, but it's considered bad practice. Unfortunately they look much the same although there are differences if you know what to look for.

I once worked in a video facility where it was a sacking offence to bring a 50 ohm BNC onto the premises!

RCA plugs and sockets have no particular impedance although as digital audio isn't very critical, they all pretty much work.

S

And to note

We are talking about a characteristic impedance here - not a resistance.

 

[tmtomh]

Now I'm curious: what exactly is a "75 Ohm connector"? Or a "110 Ohm connector" in case of AES/EBU cables?

This is not just semantics. We're supposed to be precise and scientific, that's the whole point of this forum.

From all I know, the connector type has precisely NOTHING to do with the type of application any cable is intended for.

You’re right - it’s not just semantics. But it is about tolerances, and for digital signals the 75/110 ohm difference doesn’t make a difference until you get into longer runs.

 

[Ropeburn]

Thanks guys, for educating me further on the finer aspects of analog/digital purpose connections. I tend to think in simple, general principles whenever audio or audio-digital connections are concerned, but there's always an opportunity to learn more. That's what I'm here for.