Anything broadcast shares the same maximum PEAK volume level, but commercials will maximize the "loudness" to fill out that headroom. Think of it as you're listening to a trio and suddenly a choir kicks - same volume, but more intensity. I've heard that commercials are louder as they anticipate people going into other rooms - like the kitchen - during commercial break and want the audio heard. It's also for effect - to capture attention in general - you can't miss that glaringly loud volume. Some newer TV's have settings that allow for auto leveling to prevent said ad blasting.My understanding is that the total programming needs to have a certain average loudness (SPL, dB) during the presentation. Advertisers want more volume to sell their product so the presenters reduce the average volume of the show, allowing more volume headroom for the advertisers. It does seem to have gotten worse recently though.