I think the phenomenon is called "tinnitus", when your ear is ringing because of an exceptionally loud sound, or imbedded ear damage. Where can I get that sound? Is it different for each person? I've heard it before, when a flashbang grenade is used in a first person shooter, the flash is accompanied with a ringing that I want to emulate...
Tinnitus is different for everyone, the frequencies are dependent on which stereocilia or hair cells are damaged in your cochlea. The closer the cilia damage is to the oval window where the cochlea is attached to the stapes the higher the tinnitus frequency.
Some people experience multiple frequencies and can even have different frequencies in each ear. If you want to recreate it, then the best place to start is with pure sine waves and add a small amount of white noise.
I've found mixing in a bit of pink noise, tightly band limited (to taste) around the 'ring' frequency, can add to the realism.
I've used this in an 'ear recovery' scene by slowing blending in this 'hiss' volume while simultaneously widening the band limit - then dissolving that into a bit of diffuse reverb as the scene's location ambience recovers...
I created a similar effect when I recorded some feedback by accident. I actually used it later on for a short film. It can be heard in the second clip right at the end here -
Try messing around with some basic sine/saw/triangle wave generator between 1 and 3 khz or so. Play around with the harmonics. To add movement to it, you can try automating some very light reverb in it or playing with the phase as well. If you automate some light saturation or resonance in it, it could make it sound more painful.
@Kyle Yeah, exactly signal generator/sine wave, but don't forget what you can do with all the other sound in picture or in the mix. Having the right sound has a lot to do with context. For example, a cut-off filter on ambiences to focus attention to the 1st person, atmo reverb up and direct low, and the classic muffled heart beat and muffled breathing (record through a stethoscope).
I have personal experience with it, and it is a wash of a few harmonics, centered around A. It gets louder and softer, depending on if I concentrate on it or not.
Sounds cool, keep us posted!
Whoosh goes the dynamite, Petr