Line cable and "instrument" cable

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Yasoo

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Anyone know of a difference between line cable and "instrument" cable?
 
Passive instrument pickups (what you find on a bass/guitar) typically have quite high impedance compared to line outputs (as you would find on a keyboard, effect unit or preamp). They also often have slightly lower levels than line output, making them somewhat more sensitive to noise.

Therefore an instrument cable must have lower impedance than a line level cable, and since the instrument cable also typically is longer, the requirement of low impadance per meter gets even higher. Also, the shielding needs to be better.

Microphones may in turn have even lower levels (condensers do in any case) and is therefore often balanced in addition, to further reduce noise. The balancing also allows you to supply phantom power.

So, in effect, instrument cable is pretty much unbalanced microphone cable. While line level cable can be made cheaper without harming the sound.

In fixed studio installations, you typically run everything with balanced "microphone-quality" cable, just so you don't have to care about which jacks are microphone jacks and which are not.
 
Cool info, Regebro. I was looking back on this post and noticed I never saw your reply.

So, can an instrument cable and line cable be used interchangeably?

Or, from reading your reply, it's O.K. to use instrument cable when connecting line level gear, but not as O.K. using a line level cable when connecting an instrument to an amp?
 
Umm......

Impedance is frequency-dependent, meaning the impedance of a particular thing will depend on the frequency passing through it.

The impedance of any cable at audio frequencies is insignificant, basically non-existent. I'm pretty sure he meant capacitance.

Capacitance definitely has an effect in TRS vs. TS cables, especially when used with a high-impedance source like an electric guitar or passive electric bass. It will have a bad effect on tone, starting with a high-frequency roll-off.

There is no difference in a TS cable you would use for guitar, or one you would use for line-level appilcations, as far as impedance at audio frequencies. Some do have less capacitance than others, a plus in instrument applications.
 
boingoman said:
There is no difference in a TS cable you would use for guitar, or one you would use for line-level appilcations, as far as impedance at audio frequencies. Some do have less capacitance than others, a plus in instrument applications.
Click to expand...

Thanks for the reply.

So, when you buy a cable labelled "instrument cable" it most likely has less capaticance than one labelled "interconnect cable"?

And less capaticance is "better" regardless of the application (guitar vs. line-level apps.)?
 
Yasoo said:
Thanks for the reply.

So, when you buy a cable labelled "instrument cable" it most likely has less capaticance than one labelled "interconnect cable"?
Click to expand...

Maybe, maybe not, if it is an unbalanced TS cable.

I should qualify a statement in my last post. It should read there is no need for a difference in an instrument cable vs. an unbalanced line cable. So many companies have used and continue to use the same cable for both instrument cables and unbalanced line cables. Differences in capacitance come from cable construction, and until recently people didn't pay attention to capacitance very much as a criteria for marketing cable to the average Joe.

If an unbalanced cable is marked as an interconnect, it was in the past an arbitrary designation, based mostly on length. A 10-footer would be called a guitar cable, and might have had a fancy cover or connectors, but the cable was the same as the one footer marked as an interconnect.

Some builders, like George L., make very low capacitance cable specifically for instruments, and use different cable for interconnects. Much of the marketing hype around cables is exactly that, hype. Things like time/phase correction, skin effect, etc. are pretty much bunk for various reasons. But capacitance is one cable characteristic that without a doubt can make a huge difference, especially in applications involving passive pickups.

So whether or not they are different pretty much depends on who made it.

Yasoo said:
And less capaticance is "better" regardless of the application (guitar vs. line-level apps.)?
Click to expand...

Well, in general, yes.
One of the big factors is the source impedance. The cable and the source, be it an instrument, mic, or piece of rack gear, act together as a circuit, a low-pass filter that rolls off high end. The higher the source impedance, the more the signal is affected. Many instruments have source impedance of 20,000 ohms or more, while line level devices are usually much lower, 1000 ohms or less. This makes them much less susceptible to cable capacitance, and so line devices can drive much longer cable runs with no effect. Think about a mixer 100 feet from stage as an example. This is also the reason mic cables can be extremely long. Most mics have a source impedance of 200 ohms or less. Most of the reason for using balanced cables in these applications is the noise reduction in a balanced circuit. Noise is also the reason people use DIs to connect unbalanced line sources to mixers or recorders that are far away.

Sometimes there are exceptions. Belden Star-Quad cable is popular because it uses 4 conductors, 2 for + and 2 for -. This ups its resistance to electronic interference over regular two conductor mic cable. It also has higher capacitance than Belden’s other offerings. But the low source impedance of mics basically takes the capacitance of the cable out of the equation unless the cable run is hundreds of feet long, as the capacitance is measured per foot or meter and adds up. Get it? :)

Couple things to think about:

Capacitance is cumulative with cable length. A short run of a cable with a higher capacitance may have less effect on tone than a long run of cable with lower capacitance.

There is a lot of buzz about guitar effects that use a "true bypass". Think about what that does. Every time you switch an effect in or out, you change the length of the cable and the total capacitance, and therefore your tone.
If you have a ten footer connected to a pedal with true bypass, and a twenty footer to your amp, when you switch the effect off you have tripled your cable length. I'm not dissing true bypass, it's just an interesting observation.
 
Very cool. That's some great info. Thanks a lot Boingoman. I really appreciate your time.
 
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