For example, of the two words lion and lioness, lion is unmarked for gender (it can denote either a male or female) whereas lioness is marked, since it denotes only females. b. Explicitly characterized by or having a particular linguistic feature.
20 Hertz to 20,000 Hertz is the frequency response range that a human can hear. So in answer to your question 20 Hertz would be the lowest pitch a human can hear.
So, dogs can hear sounds that human cannot, for example: bats: they use ecolocalization yelling sounds from 14 kHz to 100 kHz, so dogs hear them better than humans do. rats: they chat at ranges from 20 kHz to 50 kHz, so ratter dogs can perfectly hear them. frogs: they chat at 35 kHz, so dogs hear them too