Here's how to play a dominant 7th chord on a bass guitar. The dominant 7th is like a major 7th chord, but with a lowered 7th - the 7th is one half-step lower than a major 7th chord. If we use G as our example, we talk about the notes in the chord as they are in the G scale. So we'll be using G, our root, B, the major third, D, our fifth, and now our 7th, which in a G major scale is F#, is now F. And this gives us our dominant 7th sound. Another way to think about it is a C major scale starting on G, and then it's arpeggiated as a chord. So we have G, B, D, and F. And here's two octaves of the G dominant 7th chord.