Topic: AES/EBU & SPDIF, what is meant by 110 and 75 ohm??

[BC]

http://taperssection.com/index.php?topic=7676.0
to summarize, you need a transformer to convert the 110-ohm AES signal to the 75-ohm S/PDIF signal. 

Funny, I was just thinking about this last night. What does the 110 ohm of AES and 75 ohm of SPDIF refer to? Input impedance of the connection?

In the same vein, I am a little confused about what it means to have 75 ohm cabling. 
Units of resistance are ohms, so how can cable be 75 ohm, since the resistance would depend on the length. (resistance=resistivity*length/area)

[keepongoin]

reistance of the cable depends more on the material than it does on the length.

[F.O.Bean]

well, technically, wouldnt a coax 75 ohm cable be more 'true' because of less resistance against the signal 100ohm aes is the PRO stuff too, so why does their signal have more resistance one would think less resistance=better/purer signal

i went to electronics school, but never understood that and never got to ask my tecacher exactly what that m,eant

[BC]

I guess if the voltage swings that represent the digital signal are the same for SPDIF and AES (no idea if this is a valid assumption or not) then for a higher resistance the current required to drive that voltage would less for 110 ohm than for 75 ohm.

Perhaps this lower current has implications for driving long cable runs, hence the tendency for "pro" use.

Just thinking off the top of my head here though, I really have no idea.          

[JasonSobel]

I know that peak-peak voltages of an AES signal are much higher than peak-peak voltages of S/PDIF signal.  something like 5V compared to 0.5V (but I think there is a range of acceptable voltages for each specification, I think AES is 3V-7V peak-peak, not exactly sure though, someone please correct me if I'm wrong.)

however, I'm not sure about the 110 ohm vs. 75 ohm question..