I would recommend the free music specialization course track at coursera. Just choose to "audit" to get the entire thing for free. you just won't get graded (by a human) you will get to see how your answers are on all multiple choice stuff.
You only need to pay if you want a certificate and human grading your work.
>This Specialization will give you the knowledge and tools you need to record and produce professional sounding music. You will begin by developing your identity, vision, and intention as an artist and producer. Next, you will learn the technical aspects of music production, including how sound is translated into audio signals, recording techniques, and effects such as reverb, delay, and compression. You will also learn how to use the industry standard Digital Audio Workstation, Pro Tools, to create professional recordings. Finally, you will apply the knowledge and tools you gained in a culminating 4-week Capstone where you will complete a project beginning at the pre-production stage through the recording, mixing, and mastering stages.