Could you try taking a musical track and doing a low-pass filter to remove anything above 100 hz? If it doesn't sound about the same to you, then that is proof that you are hearing and processing some sound above that 70 hz limit. The inability to distinguish speech sounds more like trouble with higher frequencies (which help discriminate between different syllables) than with frequencies in the 100-400 hz range typical of human speaking f0s - because the latter are also vital to what tends to make music sound full and rich.