Digital XLR vs. Analog XLR - Balanced Cables

The analog vs digital XLR cable construction, materials etc are not going to make any difference - if indeed there is any difference in construction. As to carrying digital signals are not going to introduce jitter with the cable. Other than compatibility with connectors, there is no benefit to using a balanced connector for transmission of digital signals - there would have to be an incredible amount of noise to corrupt the digital signal, and if there were, the effect would not be in the least bit subtle. There is benefit in balanced connections for analog signals - assuming, of course, that the connections are actually to balanced inputs.

The only thing about cables that is going to make any difference as to jitter is whether the cable has sufficient bandwidth so as not to cause jitter due to the inherent characteristics of the data signal itself. Even then there should be correction circuitry at the converter stage to correct for any transmission induced jitter. Likely, the analog and digital versions of the XLR cables both exceed the bandwidth necessary to avoid transmission induced jitter.

As to characteristic Z and BW: First, the reason to set a characteristic impedance of a cable is to reduce transmission line effects. T-line effects amount to standing waves. These only become important when the wavelength of the signal approaches the length of the cable – how far the signal has to travel. So, whether or not a given and specified characteristic impedance of a cable will matter depends on the cable length. So does the bandwidth of the cable, for that matter, because the total capacitance is determined by the length of the cable. As between the two, as I will explain below, the bandwidth is going to be more important, for the lengths we are talking about.

As to the reference to the Stereophile article – not exactly a reference that is going to add validity to a technical position when posing such position to an engineer. Next time try something a little more accepted in the scientific / engineering community – such as an IEEE journal, or even something published by the AES or the ARRL.

As to the transmission line effect, we are talking about interconnects here. I made the assumption that the lengths are somewhere in the neighborhood of less than 10 feet. T-line effects only kick in when the wavelength of the highest signal component approaches the length of the cable. Standing waves, if they are present, will tend to round off the edges of the square pulse, this is what causes the jitter due to T-line effects. The purpose of selecting the characteristic impedance to match the source and the load impedances is to get rid of T- line effects.

The highest signal component in the case of digital audio will be about 10 times the fundamental frequency of the signal because at that frequency you have a nicely shaped square wave.

The wavelength of a 100 MHz signal is just under 10 feet, so you really aren’t getting T line effects until you approach that cable length, if we are talking about a signal with 100 MHz components. A safe rule of thumb is a 1 to 10 ratio, so there one could argue that to completely eliminate the possibility of T-line effects the cable should be less than 1 ft long. However, the transmission rate of digital audio at a 96 kHz sample rate isn’t 100 MHz. If you go out two decades, you are still at only 10MHz, which is a wavelength of just under 100 ft. Hence, a 6 foot interconnect will not be a source of jitter due to T-line effects.

More likely (but still not very likely) is that the rounding of the pulse will be due to bandwidth limitations. If the cable has too high of a capacitance value, it is possible to create a low pass filter that will start rounding the square wave and create jitter. The chances of that happening are also slight at the lengths we are talking about, but more likely and does not depend on the creation of a standing wave. For that reason the bandwidth of the cable is more important. A subtle difference, but there is a difference.

But, on a practical side – it just doesn’t matter – a cable made for analog transmission will work find up to about 50 feet and most interconnects for home audio are not that long.

Remember also that jitter only becomes a problem at the conversion. Circuitry at the convertor should reconstitute the clock and reject jitter that is not extreme.

Is it a big deal, no – not if you are purchasing the IC’s new, I haven’t priced digital vs analog IC’s but there is no reason that one should be significantly more expensive than the other. Furthermore, since the 110 ohm low capacitance cable is not going to cost significantly more for 6 foot lengths and it will work just as well for analog, my guess is that reputable sellers simply make up all their cables out of the same cable and connectors and just charge a small amount more to sell you one rather than two cables; i.e. $ 60 /pair vs $35 each. Not unfair.

Funny, I have found IEEE journals to be understandable. As to the attempt at an explanation in your last post- it makes no sense.

The last explanation about slew rate and ignores the relationship between the two. A little background in Fourier theory may clear up the lack of understanding as to the relationship between signal shape, frequency, and slew rate.

Your home audio equipment is not going to miss pulses by the changes caused by sending a pulse with fast rise and fall times through a path with a bandwidth typically available through analog interconnects.

As to T-line effects, the explanation misses the forest for the trees. The ultimate problem caused by standing waves is the rounding of the pulses.

The text proffered in the last few posts were simply lifted from elsewhere and offered as an explanation. But, they are out of context and inapplicable to the discussion at hand, which is whether digital vs analog IC's make any difference in home audio interconnects. If the person who initially posted the question is using the cables to transfer audio data in a typical fashion, i.e. from for eg. a CD transport to an outboard DAC, he doesn't need 110 ohm interconnect to do so - whcih was my original statement.

What is amazing is that this posts from Kijanki started out with a statement that bandwidth made no difference when it comes to jitter, but yet now offers quotes that refer to the importance of bandwidth. The reason for this contradiction appears to be a lack of a firm grounding in the meaning of the terms and effects discussed i.e. slew rate, frequency, bandwidth, and t-line effects.