There are some secrets... like the CAGED system for guitar (and bass too). That was a pretty good secret for many years. And when learning guitar chords, nothing beats Johnny Rector's method. James Jamerson and Ray Brown took some "secrets" with them 'cuz no one has done it since. My "secrets" for bass are all borrowed from others. Not getting complicated with scales is a big one. Just maj7, min7, dom7, dim7 - the vocalist or soloist only need these notes. They're already singing the 11ths and lowered ninths. The chord progression dictates all one needs to play. In fact, the bassist guides the entire ensemble along the progression (the drummer is the true bandleader, then the bassist - the rest can make any noises they want and it will sound good). The most important "secret" of bass is physical skill - getting your tone in the fingers, because a hundred notes will never beat good tone for audience appreciation. Learning to weave arpeggios and inversions into a musical line and exhausting the notes from one position before shifting into the adjacent position. And the best secret is the magic of open strings - as Tommy Tedesco said, the open strings and first four frets are the "money notes" - perhaps all you really need...the rest of the neck says "Look at me! I'm a star!"
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