Garageband is free but is mostly overkill for recording audio notes. What’s really needed is a Mac app dedicated to notes and audio recording, or a simple audio recorder that’s quick and easy to use. Try iScream. It’s free. It’s easy. It works.
What you get is simple recording and management. Audio is captured from the Mac’s built-in microphone, or any other audio input device. Open iScream, click on the red record button, and record audio. Clips are saved and listed below the audio transport controls.
Preferences are nominal. Select the Recording Device. Select which action occurs when pressing the iScream icon. You can even setup specific hotkeys to avoid using the mouse or trackpad. I prefer to put iScream in the Mac’s Menubar.
Other preferences include Output options. Select the audio file format (AAC, MP3, WAV), number of channels, the sample rate and bit rate. You can also specify the folder to save audio clips, and even elect to have a date and time stamp inserted into the file name.