Re: lower pitch, I'd hazard a guess that you're basically reducing the restoring force, so the resonant frequency goes down. Think of the attachment point as a bunch of springs in parallel; you snip a few of them and the overall spring constant is reduced. Or another way to think of it: Imagine you had a reed of a given width and then added mass to the end by making it wider at the non-attached end. You'd expect the frequency to go down.
I'm sometimes tuning accordions, which is rather similar, but if you want to lower the tone by a lot, you can plop some solder close to the tip of the reed.
It's pretty clear why that's the opposite of filing off material close to the tip, so obviously the tone goes lower.
In my mental image, filing close to the base of the reed gives the reed a similar shape as putting extra material next to the tip (thinner at the base, thicker next to the tip), and that's why it behaves the same.
The solder on the tips reminds me of a doctor visit years ago. I thought I may have broken a finger, and when I got to the doctor's office I mentioned to the receptionist that I had a high-deductible (HSA-compatible) insurance plan.
The physician's assistant said, "We could send you over for an X-ray, but since you're paying out of pocket, we can start with a simple test." He pulled a contraption out of his desk drawer and asked, "Do you know what this is?"
I said, "Yeah, a tuning fork. And based on the size and those heavy weights on the tips, it must be tuned to a rather low frequency."
He said, "Yep. So we get it vibrating and then touch the base to your finger. If you have a fracture, it will hurt because of the broken bone ends jiggling against each other. Then we will go for the X-ray to get more details. If it doesn't hurt, you are good to go. Is that OK?"
"Sounds good to me!"
It didn't hurt at all, and I just had to pay for a simple office visit instead of an expensive X-ray.
