My red Heeler was stone deaf at about 11 years. No matter though because she knew my routines and her duties brilliantly. She was also a lip reader.
Our Pomeranian Mix Nemo can hear high pitch sounds perfectly(Good thing I talk loud) otherwise his hearing isnt so good..but he understands everything, especially food, heck he will come and start barking when its time for his breakfast/lunch/dinner..I think they have clocks in their tummies lol