M T:
As a followup question, is it OK if I make the tinnitus my object of meditation?
Well, in my opinion, that may depend on how you might want to use that object in the future. You are much better served to ignore the ringing or humming sound and to concentrate on watching the breath or the movement of the abdomen than you are to listening to that noise. This is especially so if you have in mind to practice
dhyana meditation at some point, as the breath just simply lends itself better to this practice.
So, in the short term, if it helps you achieve a quiet mind, then fine, as far as that goes. I not sure you'd be able to identify a pleasant sensation by focusing on the sound, but then I'm open to being proven wrong on that count! It's just not something I've tried, therefore it is not my cup of tea. That's not to say that it can't be yours.
M T:
As mentioned above, the quieter my mind is the more apparent the mental vibration becomes, so in a way it seems like a metric for how well I'm meditating. Is this a naive way of doing things?
On the contrary, generally speaking, whatever helps you be able to determine a pleasant abiding in meditation can be used as a
nimitta or sign, just as you have mentioned here. I use a sensation of pressure in the center of the forehead (similar to a headache, but without the throbbing and the pain of a headache) that feels like a balloon is being expanded inside the skull. I associate this sensation with an increase in concentration, because this is how I've always associated this sensation. You might say that I've conditioned my response to this sensation, but it also happens to be true: my concentration
does increase whenever this occurs. During meditation, that increased concentration upon a single object is known as
samadhi. So it can't necessarily be all
that bad.
If you are able to do that with sound, more power to you!
