Digital vs Interconnect Cables - Difference?

All three AES/EBU, coax S/PDIF and optical S/PDIF in home systems are different forms of S/PDIF protocol. One of the main differences between protocols is that AES/EBU does not contain digital copy protection while S/PDIF does. What comes to balanced (XLR) input of my DAC is S/PDIF protocol that shouldn't be called AES/EBU. To avoid confusion I would also call them by type of connection/connector: unbalanced (or coax), balanced (or XLR) and optical (or Toslink).

05-22-13: Mtruong34
I thought for digital, XLR connectors are for AES/EBU standard and RCA/BNC are for SPDIF, not balanced vs unbalanced?

We are almost saying the same thing.

The electrical form of S/PDIF (as distinguished from its optical form, which of course is a different story altogether) is unbalanced, while AES/EBU is almost always balanced.

The reason I say "almost" in both of the preceding paragraphs is that an unbalanced form of AES/EBU exists. As indicated in this Wikipedia writeup, "the AES-3id standard defines a 75-ohm BNC electrical variant of AES3. This uses the same cabling, patching and infrastructure as analogue or digital video, and is thus common in the broadcast industry."

So it is a bit more precise to distinguish between XLR and RCA/BNC connection of digital audio signals on the basis of balanced vs. unbalanced, rather than AES/EBU vs. S/PDIF, if only one of the two sets of terms is being used, and if the context does not make clear what is being referred to.

The first table in this Wikipedia writeup is also informative.

Regards,
-- Al

Relax I can't give myself the highest grade too!

Back in the early digital days the biggest difference between digital and analogue cable used to be the quality of the copper used, together with the design consideration regarding impedence etc... as identified in the previous posts.

The quality of the copper together with it's design features allows the digital signal to be transmitted "cleanly" i.e. as a square wave at very high frequencies - much higher than the analogue bandwidth.

With digital, it is very important that rise to the top of the square wave, it's duration at the top and it's subsequent return to the zero position creates as close to a square waveform as possible, so that the receiving equipment, e.g. a DAC, can recognize each "bit" of data that is transferred.

Since the advent of digital, the quality of copper used in all cables has improved to the point where "Analogue cables" will work quite nicely when used for digital purposes.

Using Digital cables for analogue will also work extremely well since the bandwidth of digital cables tend to be very high (MHz - GHz) - far in excess of the analogue signal requirements (kHz). However, digital cables can have a higher capacitance/impedence than analogue cables, which can colour the sound.

So what's missing from digital, as implemented in the audio world?...

> When a computer transfers digital information to a USB stick there is a series of checks and balances performed to determine if all the data, in a spreadsheet for example, has been received by the USB stick - if not it is re-sent. After a few failures the process generally issues a warning and halt the transfer.

However, with digital transfers to a DAC (e.g. internet streaming or data from a CD transport), you never know if all of the signal gets to the DAC because the "checks and balances" are not performed and the DAC "fills in" the missing information and still manages to create a very good analogue signal.

So, using an analogue interconnect may sound as though it's working very well, but the DAC is actually making it sound that way.

Using a digital cable will not "guarantee" all the data gets to the DAC either, but the success rate tends to be significantly higher, because they are designed for digital transfers.

My own personal experience with digital cables has proven to me that using a digital cable with the highest bandwidth available (currently using 150mbs) improves the analogue signal from the DAC significantly.

Using highest bandwidth optical cables available also results in significantly better sounding music.

However, I still use analogue cables for analogue signals.

One day the two may converg and we will simply have "interconnects"

BTW - subwoofer cables are designed specifically for extreme low frequncies - you can use a regular interconnect or a digital interconnect, but they won't work quite as well.

RO817,
I'll give two examples of companies that use the identical cable for digital and analog use. ASI Liveline and it was very good in my system (one of the best soundihg I've heard).I'm currently using the High Fidelity CT-1Ultimate digital cable and it's just outstanding! Superb natural sound.
Regards,

Excellent elaboration by Kijanki, with which I agree 100%. An important bottom line point in his post is that a "cable that is perfect in one system might work poorly in another."

Marakanetz, any designer of an electronic system (audio or otherwise) who creates a design in which digital signals whose waveforms have any kind of criticality are transmitted through a cable whose impedance match to the connected components is random and arbitrary should be fired and/or sent back to school, IMO.

Which is not to say that it won't work ok in some cases. But why design a potential problem into the system, when it is easily avoided?

Regards,
-- Al

whoever tells that you can't use analogue cable for digital signal indeed never had tried that.

I'd like to expand a little on Al's excellent (as usual) post. Each cable has characteristic impedance. This impedance depends on cable geometry and dielectric and can be simplified as SQRT(L/C). When this impedance is different from the gear impedance, that cable is connected to, we will get transition echo from point of impedance change back to the output. Severity of this echo is dependent on the amount of impedance mismatch and slew rate of transitions in digital signal. This echo might reflect many times inside of the cable colliding with original or next transition. This collision will change the shape of transition from smooth swing to jagged one. Jaggies in transition will effect moment in time when logic level change is recognized at certain threshold voltage, resulting in time jitter that D/A converts to noise. Slow transitions would help to reduce this effect but will make system more susceptible to similar jaggies induced by noise that is either picked up by the cable or exists in the gear itself. Very fast change will reduce effect of transition jaggies (shorter time=shorter time variation) but will require better match of cable and gear impedance. 75ohm and 110ohms are standards agreed upon so that we know what we're matching to, but it could be any number. Cable might have 85ohm and it is fine as long as gear happens to have also 85ohm. That's why it is all system dependent. Cable that is perfect in one system might work poorly in another.

Let me try to explain jitter. Imagine sinewave created by series of many equally spaced dots (each dot corresponds to one D/A conversion) - like dotted line. Connecting dots together will result in smooth sinewave - that's what filter does. Now make time distance between dots different (alternate shorter-longer) and repeat connecting dots (keep each dot's amplitude - move in time horizontally). Sinewave will become less smooth. It will have jaggies, like if another frequency is on the top of it. That's what jitter does on analog side. It creates additional frequencies of very small amplitude. With music (a lot of frequencies) jitter will create a lot of additional unwanted frequencies - a noise that is only present when music is present. It shows as a lack of clarity. If you look at this sinewave again you'll agree that size of the jaggies will grow with amplitude of original sinewave. Jitter induced noise is proportional to loudness/level of the music. Digital is not only 0s and 1s but also their moment of arrival, unless music is transferred without timing as data (hard disk, WiFi, Ethernet etc.) Eventually timing has to be recreated for D/A conversion introducing possibility of jitter.
A/D conversion also suffers from the jitter. Artifacts become embedded in digital file and cannot be removed. Many original recordings were digitized poorly with unstable clock and the only option is to do it again if analog tapes still exist.

Almarg wrote "Both analog and digital interconnect cables can be had in balanced or unbalanced configurations. Balanced cables utilize XLR connectors. Unbalanced cables usually utilize RCA connectors, although BNC connectors (which are superior to RCAs) are used occasionally."

Is this true for digital cables? I thought for digital, XLR connectors are for AES/EBU standard and RCA/BNC are for SPDIF, not balanced vs unbalanced?

After Al's eloquent posting above, I wanted to clarify my comment.

Can you use an analog cable for a digital cable and a digital cable for an analog cable? Yes, you can, (assuming the connectors are the same). Should you, no probably not, but in a pinch, no harm will be done...other than perhaps a sonic degradation of the signal.

You should always use the proper cable for the application.

Can someone explain the difference between digital and interconnect cables?

A digital cable is a form of interconnect cable, that is designed to conduct digital signals. Another form of interconnect cable is one that is designed to conduct analog signals. I believe that your question is intended to address the differences between digital interconnect cables and analog interconnect cables.

Both analog and digital interconnect cables can be had in balanced or unbalanced configurations. Balanced cables utilize XLR connectors. Unbalanced cables usually utilize RCA connectors, although BNC connectors (which are superior to RCAs) are used occasionally.

Balanced digital cables have 110 ohm impedances, and are NOT coaxial. Unbalanced digital cables have 75 ohm impedances, and are coaxial.

The impedances of analog interconnects may or may not be specified or well controlled.

As Mofi indicated, any of these cable types will function in both analog and digital applications, as long as the connector types match the connectors on the components that are being connected.

IMO, however, using an analog interconnect to conduct digital signals is poor practice, and stands a good chance of being sonically non-optimal. (In saying that, I'm assuming that the manufacturer does not specifically indicate that the cable is suitable for digital as well as analog applications). Digital signals involve vastly higher frequencies than analog signals, which means that a poor impedance match will degrade waveform quality, which in turn may (depending on many system-dependent variables) degrade sonics.

Using a digital interconnect to conduct analog signals stands a good chance of working well, IMO, but depending on the design of the specific cable MIGHT not work quite as optimally as a similarly priced cable that is intended for analog applications. There are several possible technical reasons for that, depending on the specific design, although I suspect that in most cases the differences, if any, would be minor.

Is digital for connecting CD/SACD transport and DAC?

Yes, that is one application of a digital interconnect cable.

How about the cables between CD player and pre-amp - Interconnect or digital cables? And between pre-amp and power-amp?

Those connections usually involve analog signals. See my comments above.

Regards,
-- Al

You can use any analog (RCA or XLR) cable in the place of any digital (RCA or XLR) cable and vice versa.

Digital cables are usually just one cable, so you would need two of them for an analog connection.

XLR connectors would need to be the correct pinout, (most are the same).

I have done this many times. It might not be the correct/proper impedance match, but it sure won't hurt anything.

Digital cables come in 2 varieties... 75 ohm rca connectors and 110 ohm xlr connectors.

They are used for connecting 2 digital components, mainly to a dac, from a cd or dvd transport.

Any connections between sources and preamps or preamps and amps would be via analogue interconnects

sometimes you will like the DAC inside the preamp and sometimes you may prefer what came inside your CD player.

I suppose there are a few components that could be considered preamps that have dac, most do not. CD players have dac's.
I use digital rca to bring the digital (1&2) signal from a transport or digital cable box to a DAC (converts the signal back to analog) to a analog rca to the pre/amp. As far as I know a regular rca ic can not transfer a digital signal.

Good question but you are going to get a ton of responces. Although an awful lot of video cables as well as audio will work as a co-ax digital cable the actual spec for a co-ax digital cable is 110 ohms not the 75 ohm viseo cable spec. It's not as simple as all that since the RCA connector used is not a 110 ohm plug either. IMO these factors lead to LOT of debate as to what cable works best for digital. I myself am a big fan of synergy so no matter what you buy make sure you can return it. IMO recommendations on cables are much more valid if they come from someone who has heard them on the same make and model of equipment that you yourself are using. Do you have your Digital source and DAC yet?

To answer your first question last, there are many ways to transfer digital signals but the most common are probably digital co-ax with RCA ends so they look like a conventional audio or video cable, optical digital with a Toslink plug which looks nothing like an RCA plug and IMO is a crappy plug and HDMI cable.

As far as what type of cable to use between a CD player and preamp, assuming you have both options, I would try it both ways as sometimes you will like the DAC inside the preamp and sometimes you may prefer what came inside your CD player.

Hope this helps.