This is a muting technique for six string bass I am working on lately. I dampen the B string with the base of my right hand and make the open E, and D strings short with my thumb while playing with index and middle fingers on the G and C string. Not easy, but very useful for playing chords and arpeggios. Especially when you don't want to turn it in blurring mess. 
https://www.youtube.com/shorts/Ytdp00HU7Lw
https://www.youtube.com/shorts/Ytdp00HU7Lw
Last edited: