Usually I want to omit background noise and be alarmed only when my baby cries. Because I'm not actively listening all the time, I only want to be alarmed when there is a loud sound. That makes a noise filter an obvious feature choice. As a pleasant side effect the data can undergo a supreme compression with a noise filter active.
Though, sometimes I also want to check on the breathing or be able to hear street noise so I know what's going on. Just to be safe, the more insight I can have the better things are.
With that I want the app to have a noise filter that can be switched on/off. Usually the filter is active to cancel any background noise. I'll switch it off when I want to check what really goes on, all the little sounds and noise.