Re: Midrange frequency questions
When you hear the crunch rhythm guitar tone on the first Boston album, you're hearing a tone with the low mids boosted. I guess those frequencies contribute to the roundness of Santana's tone too. The early Boogie amps he played through a lot boosted the low mids. They contribute to fullness and crunch. You can hear a boost in the lower mids when you move your wah pedal down below the middle of its travel. Not all the way to the bottom, but below the middle point, where it starts to sound like an "ohhhh" sound. Not an "ooooo" sound though.
When you hear George Lynch's tone on his Lynch Mob albums, you're hearing a tone with more of a boost in the upper mids. You can hear an upper mid boost when you push a wah pedal up past its mid point of travel. Not up at hte top so it goes "aaaah!" but a little past the middle where it kind of goes "aw".
If you have an EQ pedal, you can use that also to experiment with boosting different frequencies and listening to what they do to the guitar tone. Boost the frequencies between 300 and 600 Hz to hear low mids. Boost between 800 Hz and 2KHz to hear high mids.