Where do cables upgrades have the most impact?

Agree with above about speaker cables, different speakers have their own kind of sounds that tend to work better with particular types of cables.  Once you’ve optimised the speaker end of things then you can isolate and play with different parts of the chain.  At the end of the day wrong speaker setup will give you wrong sound.

Info from audio shops indicated order of importance #1 power cord, #2 interconnect followed by speaker cable

My experience is as follows:

1) I/Cs and digital source power cables

2) speaker wires

3) power cables

Mishan 12-3-2018
Using the example of intercon cables (the same manufacturer and the same model), I can say that in most cases a cable 1 or 0.8 meters long sounded better than half a meter long. I suspect that the matter is in some "wave" nuances, but I would be happy to know the expert’s opinion.

I assume you are referring to line-level analog interconnects.

Most cable parameters are directly proportional to length, including resistance, inductance, capacitance, the resistance rise that occurs at high frequencies due to skin effect, the effects of the resistance of the shield or other return conductor on the susceptibility of the connected components to ground loop issues, the effects of dielectric absorption, propagation delay, etc. (In mentioning these parameters, btw, I am putting aside the question of whether or not any of them may be great enough in degree to be audibly significant in a 1 meter analog interconnect).

The only parameters that occur to me that are not directly proportional to length are what is called "characteristic impedance," and susceptibility to RFI (radio frequency interference) at some frequencies. Neither of those seems likely to be relevant to the sonic effects of a 1 meter interconnect conducting analog audio signals, however, assuming the system is not in an environment having unusually high levels of RF.

Therefore it seems to me to be a good bet that your 1 meter interconnect has more effect on the sound than your shorter interconnect, and that increased effect is simply more complementary to the sonics of the rest of your system and/or your subjective preferences.

Putting it all another way, the "shorter is better" philosophy assumes that the goal is for the cable to have as little effect on the sound as possible, at least in the case of a line-level analog interconnect.

It could very well be a different story in the case of a digital interconnect cable, though, as explained in this paper. And perhaps also in the case of a phono cable, depending on the particular cartridge and phono stage, due to a number of effects that can result from the interaction of the capacitance of the cable and the inductance of the cartridge.

Regards,
-- Al