"Yeah, my son sings hetero"

The oldest is hearing impaired. He has 90% hearing loss in one ear, which basically removes all depth perception (he can't tell where sound is coming from) and distorts how he hears his own voice. He wears a hearing aid for school, or he can't separate the teacher's voice out from the background noise. But when he comes home from school, he usually takes it off, or he tends to get audiological exhaustion.

So we're in the car on the way to karate tonight, and a song he likes comes on the radio. He begins to sing along. He loves music, so he's really belting it out. And hitting maybe every third note.

heterophony
noun
The simultaneous playing or singing of two or more versions of a melody.
"heterophony." The American Heritage® Dictionary of the English Language, Fourth Edition. Houghton Mifflin Company, 2004. Answers.com 08 Nov. 2005. http://www.answers.com/topic/heterophony