Hi Jeff,
My experience -not very vast- was that when the ringing started my doctor
(who is also my sister-in-law) had me have an audiometry. After the test and
because of the stimulation with different frequencies, the ringing had all but
disappeared but it came back after a while. That is why I recorded some of
the frequencies and am hearing them in my iPod.
The ones I now have are similar to the sound of the sea, or putting a seashell
to your ear. I believe that higher frequencies more akin to the actual ringing
would help more, but I have to experiment. Will report back.
JC