Sine Waves for use as relief for Tinnitus, as audio masking. Also, for testing PA's, speakers and other audio equipment.
These Sine wave downloads are single solid tones which are rounded, and pure in sound, corresponding to a uniform circular motion.

Preview files below, they are set at specific frequencies.
Listen at a low volume, remember you are not 'blasting out' or 'covering up' the tinnitus. There will be a 'mix-point' (often very quiet) where the audio can possibly cancel out the ringing in your ears.
It's worth trying a variety of sounds and waveforms to see what suits you best.