In article , "Yoan Paquet"
writes:

Is there a major difference between the output quality of RCA jacks compared
to Coax?

I suppose the question is, is there a difference between RCA connectors and
other coaxial connectors (F, BNC, N, SMA etc. etc.). The answer is: Of course
there's a difference. For one thing, RCAs have no standard impedance. F = 75
ohms, BNC = 50 or 75 ohms, N = 50 and so on. The next question is: does it
really matter?

The correct impedance for digital audio cables and connectors is 75
ohms.(There's a whole other posting if you want to know WHY 75 ohms was
chosen.) In high frequency 'transmission line' systems, of which digital audio
is one, the critical distance for impedance is a quarter of a wavelength at the
frequency you are operating at. If your transmission line (i.e, cable and
connector) are the wrong impedance, they will reflect a portion of the signal
(depending on how far off the chosen impedance they are).

What is the frequency of digital audio? It depends on the sampling rate. What
is the sampling rate? 44.1 kHz. (If you are running 48 kHz, 96 kHz or
anything else, you can easily modify these calculations, but I will stick with
44.1 kHz for this example).

AES standards say the bandwidth of 44.1 kHz can be calculated by multiplying it
by 128. 44.1 x 128 = 5.6448 MHz. The wavelength of that is 300/5.6448 (that
answer comes out in meters, multiply them by 3.28 to get to feet) = 174 ft.
One quarter of that is 44 ft. That simply means that the cable, connector, or
anything else that the digital signal passes through would have to be at least
44 ft. before it would have an effect on "return loss" (reflected signals) .
(Some people say 1/10th of a wavelength or 17.4 ft..)

Either way, the length of one connector, regardless of the type or style, will
have no effect on the impedance, and therefore no effect digital signal. In
fact, the cable itself will have no effect in home home installs, because the
cable is very short.

However, the capacitance of the cable will have an effect since we're talking
about data, so low capacitance is better than high. Connectors might have a
ruggedness factor, a retention factors (RCA's call become intermittent or fall
out) and therefore a resistance factor. But that's about it.

Alternate opinions?

Steve Lampen
Belden Electronics Division
somewhere over the Pacific about to land in Japan