SLA - Source Level Adjustment: Allows you to adjust the volumes coming from different sources. For example, AM radio may be softer than FM radio, so the SLA of AM can be turned up to prevent any huge change in sound levels when switching between sources. All radio is normally louder than music, so to prevent being blasted by the radio when you turn it on, it's SLA can be turned down. SLA for each source can vary from (+4) to (-4). I have also found that SLA can make a difference when subs are hooked up. If you have extremely loud subs that swamp out all of your highs, you can turn the SLA on the CD source up to make up for it. What it does is it raises the volume of the speakers without turning up the level of bass from the subwoofers.