Free download and install Filmage Audio Device to record audio on your Mac.
Two option for system sound recording: Auto Settings and Manual Settings.
Auto Settings(Recommended):
1. After successful installation of Filmage Audio Device, you just need to open Filmage Screen;
2. Click Screen on the homepage and choose the area you need to capture;
3.Then in Audio Sources option, tick System Sound under Audio Sources(Auto), then Filmage Screen will do the rest for you automatically;
4. At last you can click Recording Button to start recording.
Manual Settings:
1. Go System Preferences -> Sound.
2. Click Input and choose Internal Microphone.
3. Clike Output and choose Filmage Aggregate Device.
4. When you prepare to record, open Filmage Screen, select an area, then choose System Audio (Filmage Audio Device) in audio sources.
If you want to learn more about audio recorder, please click Here.
If you want to know how to create Aggregate Device and Multi-output Device, please click Here.