This is a very newbie-ish question, so bare with me.
Let's say the guitar plays an Asus, G2, D, Bm7, Bm9, (Key D) etc... How do you determine what to play with these chords? I'm assuming I'd play a D when the guitarist plays a D chord, but I'm confused with the rest. I've played bass for a while, but typically by ear (and not very well). I've picked up a few books that I'm working through, but still on the search for a good instructor. Care to help me out a bit?
Several ways to go on this. Here is a starter.
1/ I'd look for some fake chord sheet music on the song. Why? I would like to know how long that Asus chord is active, i.e. how many beats will that chord hang around. That will give me an idea how many notes of the Asus chord (A-D-E) to use. If the song is in 4/4 time just four A quarter notes may work OK. Or A-D-E-A may be called for - four 1/4 notes to fill the measure.
Then I would decide how many of the chord's notes to use in my bass line.
Asus has these chord tones A-D-E
G2, has these chord tones G-A-D
D, has these chord tones D-F#-A
Bm7, has these chord tones B-D-F#-A
Bm9, has these chord tones B,D,(F#),A,C# The F# is normally omitted - the rhythm guitar guys only have four fingers -- as they will not be playing the F# and it is the 5th, you may want to put it in your bass line.
http://www.looknohands.com/chordhouse/guitar/index_rb.html
OK right at first just use the root or name of the chord. For the Asus chord just play A notes for as many beats as the chord is active. Do the same with the G2 chord - just play a G note for as many beats as the chord is active. When you can do that and the music does not go off and leave you - then add the root and the fifth note.
Asus -- A, B, C, D, E - E is the fifth note so play A on beat 1 and the E on beat 3.
Fake chord sheet music will have the lyrics with the chord name over the lyrics that it is harmonizing. Usually one note per lyric word works out. Two syllable words get two notes.
Now I cheat and use the major scale box pattern. Place the box pattern's R (root note) over the chord's name note on your fretboard and all notes in that scale are waiting for you. Place the R over the A note on the 4th string 5th fret and the 4th and 5th await you. Asus = R-4-5 intervals of the A major scale.
Code:
Major Scale Box.
G|---2---|-------|---3---|---4---| 1st string
D|---6---|-------|---7---|---8---|
A|---3---|---4---|-------|---5---|
E|-------|---R---|-------|---2---|4th string
You picked some sophisticated chords, normally its not this hard.
OK ask specific questions from here.