Anyway, I've been playing for about 6 months and I'm coming along great. I enjoy the slap bass and I can slap the E string very well, but the adg strings are harder. I am working on the a string right now. I am always accidentally touching the e or d string.
Even seasoned players with great accuracy using their thumb will hit adjacent strings.
Even hitting the string square on will not guarantee that the other strings WON'T ring. You are, after all, hitting your bass with enough force to drive one string - why not 3 or 4? Ever bump your bass' headstock against the wall with the volume up? Yep. You got it.
For me, the key was MUTING with my left hand. If I'm aiming for a given string, I keep the other strings muted. Experiment with curving your finger over the A string (meaning touching the G and E strings without muting the A) while hitting the A with your thumb. Muting takes a while to get the hang of; it's almost an "anti-technique".
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