People with impaired hearing are deaf and dumb. The inability to hear affects neither native intelligence nor the physical ability to produce sounds. Deafness does not make people dumb in the sense of being either stupid or mute. Deaf people, understandably, find this stereotype particularly offensive. Hearing aids restore hearing.
Hearing aids amplify sound.
They have no effect on a person's ability to process that sound. In cases where a hearing loss distorts incoming sounds, a hearing aid can do nothing. All deaf people can read lips. Some deaf people are very skilled lipreaders, but many are not. This is because many speech sounds have identical mouth movements.