Callaham guitar parts

From an engineering standpoint, cryogenic treatment of metal parts does influence their grain structure and makes them stronger and more durable. This is important for critical parts where failure of the part could be a very bad thing, such as the big nut that holds the rotor on a helicopter (an exaggeration, but that's the idea).

Guitar parts are not subject to the kinds of stresses cryo treatment is intended to reduce. Any claims of tonal improvement are 100% snake oil.

Think about it this way: if cryo treatment of guitar hardware really did improve tone, (1) many pros would be using it, and (2) Callaham would still be using the process and simply letting word of mouth do all their marketing. Neither of these examples is true.

Yeah, they do make nice parts and they pay a lot of attention to polishing and final appearance.

That cryo treatment makes a very real difference to a material is 100% factual and demonstrable. That part is not at all snake oil. I've been experimenting with cryo fret wire. I don't know if it lasts longer (that is a hard test to do, unless the difference is extremely obvious), but it definitely feels different under my tools. They feel slightly harder and less gooey. They cut with more of a snap. I'm comparing the exact same brand and size of wire that I have used on a regular basis, so I trust my own subjective senses on that.

For guitar hardware, off of the top of my head the three things that will affect tone the most are 1) mass, 2) shape (i.e. break angles over saddles) and 3) resonance. Cryo won't affect 1 or 2, and 3 is an interesting thought. It is plausible that the native resonant properties of a material will change after cryo treatment. Some people have sworn by cryo stuff for banjo hardware, but who trusts banjo players? Where I'd be looking for good data would be the drummers. Cymbals are probably the instrument that magnifies tonal properties of metals more than any other, and by a large degree. Cymbal makers have probably the best ears for timbre among instrument makers out there, too. When the rest of the world is hearing things in terms of 3-band eq, they're hearing decay and subtle harmonics that most computers won't be able to pick out. A quick google search for cryo treated cymbals doesn't return much except a few message board discussions that don't seem scientific. Most seem more interested in cryo treatment for durability than for tone.

There is some talk among brass/wind instruments, but I don't see much about A/B comparisons.

My gut tells me that if the jury is out on brass instruments and cymbals where the metal is a huge component of the tone, then it is likely not impactful enough on guitar hardware. I'm open to good data, though.

Very true, but I think decently trained human senses are very sophisticated. It takes some very high tech stuff that has only gotten decent in the past few years to recognize faces or voices, but toddlers can do those things easily. Picking voices out of a room full of noise, echo location, hearing the difference in rooms, we're able to do an awful lot that would be tricky given just measuring equipment. Something might be behaving differently only in a very narrow frequency band, but it could be right in the sweet spot where our ears pick up on it immediately.

Also, our ears can be good at masking differences, too. We're pretty bad at judging volume, and need good measuring equipment for that because our brains are natural auto-levelers.