Volume Mixer lets you control your Mac's volume, app by app Ever been annoyed by one Mac app blurting out sound at a volume that's too low, while the next is too high? Well, shocker! There's an app for that. It's called Volume Mixer. This simple app supercharges your volume control on a Mac by allowing you to easily lower or raise an app's volume on an app-by-app basis, thanks to an individual slider.