Speaking in an abnormal tone, pitch or rhythm is among the symptoms that indicate a child has an autism spectrum disorder, notes Helpguide.org. Children with autism who talk loudly often don't know they're doing so, while others don't understand why talking in a loud voice isn't always socially appropriate. They also may not understand how changing the volume of their voice communicates different messages.
Explain to your child that using a loud voice is not appropriate for certain situations. She might not realize her behavior isn't proper. For instance, it may not occur to her that it's not OK to talk out loud in church, at the movies or in the library. She needs you to tell her.
Teach your child to control the volume of his voice. Show him examples by demonstrating what volume of voice he should use when talking to you, to his teachers in the classroom or to his friends out on the playground.
Tell your child that when she is standing or sitting close to another person, she doesn't have to talk loud for that person to hear what she's saying. Come up with a signal between the two of you to let her know she's talking too loudly and needs to lower the volume of her voice.
Monitor your child's social relationships with others. Pediatrician and child care expert Dr. William Sears points out that while children with autism spectrum disorders may interact appropriately with some individuals, they may not relate as well with others. Parents should try to avoid situations that cause a child to become frustrated, leading to socially inappropriate behaviors like talking too loudly.
Ask your child to use his softer voice indoors and save his louder voice for when he is playing outdoors. Point out that you are using your indoor voice while you are talking to him.
Act out different social situations with your child. Pretend play gives her the opportunity to practice varying voice levels for different settings, such as at home, school, the dentist's office, supermarket or outdoor recreation. Keep practicing so that she hears and learns the differences in volume.
Prepare your child for certain social occasions in advance. For example, let him know that you will be attending a public event later in the day and then practice the kind of voice he needs to use there. While there, occasionally remind him that he needs to talk in a softer voice.