I'm not going to address the production mechanism,1 just the nature of the "sound" in this case.
What you think of as the hard vacuum of outer space could just as well be seen as a very, very, very diffuse, somewhat ionized gas. That gas can support sound waves as long as the wavelength is considerably longer than the mean free path of the atoms on the gas.
As for the tone, there is a simple relationship between the tone of the same name in different octaves, so once they know the dominant frequency they can figure its place on the scale.
1 Though it won't be happening inside the event horizon -- which is where "not even light can escape" holds -- but in the region around the hole proper where it accumulates gas and dust and the magnetic fields from the hole play merry havoc with the ionized components of the accumulated stuff.
Congratulations on finding a method for baryogenesis that works! Indeed, it's true that if you have a bunch of black holes, then by random chance you'll get an imbalance. And this imbalance will remain even after the black holes evaporate, because the result of the evaporation doesn't depend on the overall baryon number that went into the black hole.
Black holes can break conservation laws like that. The only conservation laws they can't break are the ones where you can measure the conserved quantity from outside. For example, charge is still conserved because you can keep track of the charge of the black hole by measuring its electric field. In the Standard Model, baryon number has no such associated field.
Also, you need to assume that enough black holes form to make your mechanism work. In the standard models, this doesn't happen, despite the high temperatures. If you start with a standard Big Bang, the universe expands too fast for black holes to form.
However, in physics, finding a mechanism that solves a problem isn't the end -- it's the beginning. We aren't all sitting around scratching our heads for any mechanism to achieve baryogenesis. There are actually at least ten known, conceptually distinct ways to do it (including yours), fleshed out in hundreds of concrete models. The problem is that all of them require speculative new physics, additions to the core models that we have already experimentally verified. Nobody can declare that a specific one of these models is true, in the absence of any independent evidence.
It's kind of like we're all sitting around trying to find the six-digit password for a safe. If you walk by and say "well, obviously it could be 927583", without any further evidence, that's technically true. But you have not cracked the safe. The problem of baryogenesis isn't analogous to coming up with any six-digit number, that's easy. The problem is that we don't know which one is relevant, which mechanism actually exists in our universe.
What physicists investigating these questions actually do involves trying to link these models to things we can measure, or coming up with simple models that explain multiple puzzles at once. For example, one way to test a model with primordial black holes is to compute the amount heavy enough to live until the present day, in which case you can go looking for them. Or, if they were created by some new physics, you could look for that new physics. Yet another strand is to note that if enough primordial black holes still are around today, they could be the dark matter, so you could try to get both baryogenesis and dark matter right simultaneously. All of this involves a lot of reading, math, and simulation.
Best Answer
Gravitational waves are measured by using a laser that is split and reflected off of two perpendicular lines with reflective targets at the ends. The 2 lasers beams are then recombined to produce an interference pattern. If everything is stationary, there will be no change to that pattern. If one leg is moving relative to the other then the pattern will shift. It is that measurement in that shift that tells us if there is a gravitational wave. Towards the end of two orbiting massive objects that speed increases and subsequently the frequency of the wave. You can then use those phase changes to create a sound wave which is known as a chirp. Individual black holes are not going to have this frequency change in general. This all works because the speed of light is constant in all frames of reference.
The questions around someone sitting in space and hearing the gravitational wave is not possible. This is because your entire self is in the system. As your space suit expand and contract due to the gravitational wave so does everything else inside the suit including the individual and the air. So there will no imposed compression on the air or space suite relative to anything else that would cause sound. So, in the end, you do not realize anything is actually happening.