TRS are for either stereo, or mono balanced. In the case of mono balanced, the additional wire is used to carry the phase-inverted version of the signal. These are more resistant to electrical noise because the noise tends to affect both the in-phase and out-of-phase signals the same, and can therefore be cancelled out.
But balanced cables are never used as instrument cables. Stereo cables can be used on some guitars, but itās very rare.
(Itās the same cable, of course, itās just how the cable functions).
If it affected the connection, then yes. If thereās enough wire still to make the electrical connection then, possibly not. Although I have had damaged cables where flexing the cable at a particular point caused a slight scratching sound, pointing to a partial failure in the shielding at that point.
āScratchyā connections are more associated with the plug ends where the shield wires (or foil) are usually bundled and soldered together to make the connection before being soldered onto the plug terminal, and the solder joint may be ādryā or even not properly soldered and just touching. The scratchy sound in this case is caused by the change in resistance or even occasional small disconnections.
Thatās fine if it works for you.
The mechanisms are the same in both case. The AI ācableā and an AI āin a boxā like the Focusrite fundamentally do exactly the same thing, and work in the same way.
A single-channel Focusrite isnāt necessarily ābetterā than your cable, although the Focusrite will be more flexible as it will support balanced mic inputs and phantom powered mics, as well as instrument and line inputs, and will support local monitoring, etc.
Personally, I recommend the Behringer UMC range over the Focusrite: they are typically as good or slightly better, and you arenāt paying a premium for the name.
In practice, some of the very cheap guitar to USB cables tend to be a bit noisy, or to have higher latency. I suspect the higher latency is because they havenāt had proper drivers developed for them, more than anything else.
As for the mechanism, it can get into the analogue signal from a poorly shielded cable, or the pickups suffering from electrical interference. This is more likely with single-coils. And itās more common in electrically noisy environments. Nearby fluorescent lights are often very noisy and a common cause of hum.
But it can also get into the analogue side through the USB connection. If the unit is powered by USB, which comes from a PC/Laptop power supply thatās noisy, some of that noise can be injected into the signal. This is because all AIs have some sort of input pre-amp before the A/D converter, and that pre-amp references the power supply. If that reference has hum or other electrical noise on it, the resulting pre-amp output will have hum on it too.
Again, better AIs may do some filtering of the USB power supply to reduce this, but itās still a potential problem.
Laptop power supplies can be a particular problem, as they normally use cheap switched-mode power supplies. The way these work naturally injects all sorts of frequencies onto the power output, unless they are filtered out. And many cheap laptop power supplies donāt have great filtering.
The only place an AI can, reasonably, have āgood noise rejectionā is within the design of its own circuits, grounding of any metal chassis, etc. But this isnāt usually where these problems occur. Usually the electrical noise is already on the signal when it arrives at the AI.
If you canāt differentiate noise from signal, then how do you reject it?
The better approach is to avoid the noise in the first place with well shielded circuits, cables, and guitar cavities, etc.
No, I donāt think I said that. Most of the consumer-end Focusrite AIs are USB powered. As are similar models like the Behringer UMC series.
Well, thereās limits on how long USB cables should be, and itās fairly unlikely you would get significant voltage drop in a typical USB cable (a few metres), so I wouldnāt worry about that.
The biggest thing to watch for with audio interfaces which have their own power supply, is ground loops, especially with laptop power supplies.
Cheers,
Keith