Quality of recorded audio is low
Open Settings -> Preferences -> Video menu in Screen Capture and select the highest available quality from Audio quality list. Close program settings, record sample video and check audio quality in Screen Capture preview window.
You can also manually set up the quality for output file when you save your recording. Click on Save As button after recording, then select Output format. Go to format settings (button with the cogwheel icon) and open Audio tab.
Select one of the codecs instead of Auto mode, then choose Bitrate type -> Custom and select the highest available value for the Bitrate. Close format settings and save your recording.
Please note that if you record from speakers and microphone at the same time and your microphone does not have acoustic echo cancellation feature, then the sound from speakers will be duplicated in the recording, since the microphone has recorded that sound for the second time. In such case you need to either use microphone with the acoustic echo cancellation, or plug-in headphones.