Connect your analog audio source to your computer. If your source includes red and white RCA jacks, use a 3.5mm RCA cable, and connect the 3.5mm plug into your computer's Line-In port. If your analog source uses a 1/4-inch audio jack (such as a keyboard or other analog instrument), use a 1/4-inch audio cable with a 3.5mm adapter for your computer.
Open an audio recording program on your PC. Some computers include recording software by default, but if you do not already have a recording program, you can download one for free online.
Create a recording track. Many audio recording programs use a process called "multi-tracking," which requires you to record your audio onto "tracks," which function as individual layers for your transmitted sound waves. Locate your "New Track" option, usually appearing on your menu bar, beneath the "Track," "Options" or "Audio" menu.
Click the "Record" button in your project window. Sometimes it appears as the letter "R," and sometimes as a small dot or circle. As soon as you click "Record," begin the process of transmitting audio from your analog device. This may include pressing "Play" on a tape deck or playing notes on an analog keyboard.
Press the "Stop" button on your software window after you finish transmitting your audio. Click the "File" menu and select "Save" to save your audio, or select "Export" to save your recording as a digital audio file, like an MP3 or WAV. The exporting option on your menu bar may not actually read "Export," but may also read "Save as Audio File" or "Bounce."