Unfortunately, as with many things, this subject can get quite complex, and has different significance in different situations.
"Characteristic impedance" is a property of a given type of cable... and it depends entirely on the geometry of the cable.
Characteristic impedance is based on a relationship between resistance , inductance, and capacitance.
NOTE that, unlike inductance or capacitance alone,
CHARACTERISTIC IMPEDANCE IS INDEPENDENT OF THE LENGTH OF THE CABLE.
For example, the characteristic impedance of RG-59 coax cable is 75 Ohms,
REGARDLESS OF HOW LONG IT IS.
However the
CAPACITANCE of RG-59 is typically around 20 pF
PER FOOT OF LENGTH.
When we're talking about microphones we're talking about very low level signals.
Therefore, we want to match the load impedance to the impedance of the microphone, to maximize signal transfer between them.
So we connect a "600 Ohm microphone" to "a 600 Ohm input".
(To be honest, with modern gear, this if often considered unimportant, and may be ignored.)
In the case of a microphone we absolutely would want to know the total capacitance and inductance of the cables...
But the reason is that the combined inductance and capacitance will act like a high-cut filter...
And, the longer the cable is, and the more inductance and capacitance it has, the more high frequency loss will occur.
(But, while the same "high-level math" applies to both, this is a very different practical issue than impedance matching of the cable.)
It's also worth mentioning that, with
LINE LEVEL AUDIO INTERCONNECTS, we are generally connecting an output with a low impedance to an input with a high impedance.
Therefore, since we have "more signal than we need", we don't bother with impedance matching, and in fact
PREFER that the source impedance be 5x to 10X lower than the load impedance
.
(And, as long as you're using a "normal interconnect" the impedance of the interconnect is considered to be unimportant.)
Where characteristic impedance becomes an issue is when the length of our cable becomes a significant part of a wavelength of the signal we're putting through it.
In that situation we want to maximize the energy transfer, not to improve efficiency, but to prevent energy that is NOT absorbed by the load from being reflected back into the system.
So, for example, we use "300 Ohm twin-lead cable" to connect a "300 Ohm broadcast antenna" to the "300 Ohm input" on a TV set.
Because both inductance and capacitance increase with length, the longer our cable is, the less signal will reach the TV.
However, if we properly match the impedances, the signal that gets through will remain "clean".
(And, if we fail to do so, we will get a weak signal, and also a poor quality signal, so we'll get a poor picture, probably with significant "ghosting" and other issues.)
UNLIKE WITH AUDIO FREQUENCIES, with video signals, the lengths of even relative short interconnect cables
ARE significant.
That's why, with video, we
DO need to match impedances, so we use "75 Ohm cable" to connect "75 Ohm outputs and inputs".
DIGITAL AUDIO also requires good high frequency performance.
Even at relatively low sample rates digital signals rely on square waves... which contain some very high frequency components.
(If the cable isn't properly matched, it can distort those square waves, making them difficult to "lock onto", which can cause problems like noise and jitter.)
The short-answer takeaway from all this is that
ALL cables have a characteristic impedance...
But it doesn't generally matter for analog audio...
In general, with coaxial cable, any 75 Ohm video cable will work well for analog audio, since it falls well within the normal range for audio cable...
However, since analog audio interconnects may or may not have a characteristic impedance of 75 Ohms, and usually don't specify it, they may or may not work very well for video.
Impedance is not the issue here, only inductance, resistance and capacitance. It's my understanding only digital cables have a specified impedance, for instance: USB=90, AES=110, Coax=75 ohm impedance. I found it curious when viewing John Siau's video in the link he stated there was a 150 ohm impedance device attached to the end of each cable being tested which supposedly matched a microphone impedance. First time I have ever heard of such but then I am no EE either.
In the case of Star Quad cables, as previously stated in another reply capacitance increases on an average of 1.5x compared to twisted pair, but the resistance will be cut in half however I have no idea how the inductance of a Star Quad cable changes.
Impedance is the combined effect of resistance and reactance; and reactance is inductive and capacitive.
