CABLE CAPACITANCE & HIGH FREQUENCY ROLL-OFF?!

Purist Audio Design answers an interesting an interesting question about the cable loss. Q: “What dictates how great the capacitance of the cable can be without causing high frequency roll-off?”…

“A: Cable loss can be described as a low-pass filter model. For example, your preamp has an output impedance of 100 Ohms, and your capacitance of your cable of your 1 m is, let’s say, 100 pf. Your high frequency cutoff would be around 16 million.

Let’s do another example. Say your preamp has an output impedance of 50k, and everything else stays the same. The high frequency cutoff would be around 32k. If we increase the capacitance to 1000, the cutoff becomes 3k.
The basic idea is that the more capacitance and interference you have, the shorter length the cable needs to be to avoid high frequency cutoff. 
To figure your cable length, you need to know your capacitance of your cable per meter, and your source impedance. These numbers are usually found in the manufacturer’s specs. If not, give them a call or email. Then, I’d use a calculator like the one here: link
We’re lucky to have sites like this one. Used to, you had to do all of this by hand or slide rule.”