Complex sentence: The highest proportion of adults with hearing loss have an age related, or noise related loss, and with both these the high frequency sounds are lost first, many of the consonants in speech are high frequency sounds, so speech becomes distorted.
Split into simpler sentences: The highest proportion of adults with hearing loss have an age related, or noise related loss, and with both these the high frequency sounds are lost first. Since many of the consonants in speech are high frequency sounds, speech becomes distorted.