Hi Hywelg,
So there's a couple different types of impedance in the circuit. There's the source impedance, which as we were saying is very high, there's the cable impedance which is essentially a capacitor which shunts the cable to ground, and there's the termination impedance which can vary depending on the amp. The way circuit gets set up creates a low pass filter, the frequency of which is determined by the combination of the source impedance, the total cable capacitance, and the termination impedance. The cable capacitance is cumulative and some cables have more than others, so as you noticed short runs of some cable can have more of an effect that long runs of another. On top of all that, you can get accumulated capacitance from where the cable connects to the plug, where the plug connects to the jack, and so on, until the termination. Often times these things don't make a big deal, but if you have a guitar with a particularly high source impedance and an amp with a particularly high termination impedance a very small capacitance can be noticeable.
So to track down the source of the filtering in your system here's a couple things worth trying. Try turning your guitar output up or down, this will change the source impedance, and even when corrected for in the amp volume will change the over system treble. Try swapping out some cables, even the small interconnects between the pedals may have more capacitance than you think if there's a bad connection. Try putting the Factor pedals in DSP bypass mode, this will change both the termination impedance of the circuit (the Factors have a 1 Megaohm input impedance) and the in circuit capacitance, this can help you determine if the problem may be with a pedal, and if so which one in particular. Finally, it's possible that one of the pedals may have a bad connection, or a bum relay, but that's the hardest thing to test and fix so it's probably best to rule out all the other stuff first.
Does this explanation help?
