Learning morse code directly from audio is absolutely essential. Once you have learned all the characters by sound, I found it helpful to listen to code at a faster level than you can handle. You will miss characters, but I found it speeds up your ability to copy well. For example, back when I was taking morse code tests for licenses, I would listen to code at 20 wpm to prepare for the 13 wpm test and 30 wpm to prepare for the 20 wpm test. The tests seemed easy. BTW, I cannot read morse code without making the sounds in my head from the visual representation.