can someone explain relation between loading and tone

[Shea]

I don't understand why the higher frequencies seem to get attenuated the most when a signal is loaded down excessively.

My conception of how loading affects a signal is that the impedance of the load and the output impedance of the signal source form a voltage divider. Setting aside any reactive components, I don't see why that effect wouldn't be uniform across all frequencies.

Or is it just that there usually is a reactive component, like the inductance of guitar pickups?

[tbryanh]

See Fig 2 in The Secrets of Electric Guitar Pickups located at http://buildyourguitar.com/resources/lemme/

Fig 2 shows that the pickup is a signal source filtered by a low-pass filter composed of the inductor, resistor, and capacitor.

The capacitor is in parallel with the load resistance that is hooked up to the pickup. When the pickup is heavily loaded, the load resistance is very small in comparison to the impedance of the capacitor. This effectively removes the capacitor from the circuit.

What you have left is a series circuit consisting or the inductor, resistor, and load resistor.

The impedance of the inductor is higher at higher frequencies, so it drops more voltage at the higher frequencies which leaves less for the load resistor.