Your father seems to be suffering from tinnitus which may occur because various reasons such as sensory neural hearing loss, conductive hearing loss, tumors etc. If your fathers condition is because of sensory neural hearing loss then hearing
aids with tinnitus maskers can be used effectively. There are other methods such as tinnitus retraining therapy. The device which you are planning to design is already available which is known as tinnitus masker which masks particular frequency of sound
Next Steps
Consult nearby Audiologist for more information about the device