The amount of desired sound compared to the amount of unwanted sound is called the signal to noise ratio.  This relationship is important when we are evaluating techology and educational placements for our children.  It works something like this:

	When your child wears a hearing aid alone, background noise is amplified as much, or more than the desired speech signal. The result can be a "fuzzy" understanding of what is said.
	When we add an assistive listening system (ALS), the speech signal is preserved and can be separated from the background noise.