......... As far as jamming - with out sheet music - I assume some stuff. 1) The chord progression. Most music will follow certain chord progressions, i.e. Country I IV V7, Jazz ii V7 I. My point your music has a chord progression that is used most of the time. Assume that and then..... 2) Root on 1. If you want more - then R-5-R-5. Still need more - R-5-8-5. Still need more throw in the rest of the chord's tones R-3-5-b7, etc. Walk to the next chord with chromatic runs. Target the next root - miss it - by 1, 2 or 3 frets then walk to it one fret at a time and be on it for the chord change. Assume what is normally done then listen and if that does not fit - adapt. Root on 1 still works.
I found Online Bass Lessons at StudyBass.com and Ed's book "Building Walking Bass Lines" to be on track and both have great value. There is one more bass line book I would recommend, "Bass lines in minutes" by Kris Berg. "Bass Guitar for Dummies" is a good refresher book, as it has a little bit of everything you will be using. Your public library will probably have a copy. Scott Devine's video lessons have great value and will be well worth your time.
My old standby chart of generic bass lines using the major scale box as a Rosetta stone may help:
Bass Patterns based upon the Major Scale box.
Code:
Major Scale Box.
G|---2---|-------|---3---|---4---| 1st string
D|---6---|-------|---7---|---8---|
A|---3---|---4---|-------|---5---|
E|-------|---R---|-------|---2---|4th string
Basic Chords
• Major Triad = R-3-5
• Minor Triad = R-b3-5
• Diminished Chord = R-b3-b5
7th Chords
• Maj7 = R-3-5-7
• Minor 7 = R-b3-5-b7
• Dominant 7 = R-3-5-b7
• ½ diminished = R-b3-b5-b7
• Full diminished = R-b3-b5-bb7
See a chord and play it's chord tones. As every key will have three major, three minor and one diminished chord it's a good idea to get your major (R-3-5-7), minor (R-b3-5-b7) and diminished bass line chord tones (R-b3-b5-b7) into muscle memory so when you see a chord your fingers just know what will work. Now the song may only give you enough room for the root, or root five - adapt and get as many chord tones into your bass line as needed. Root on 1 and a steady groove from the other chord tones plus something to call attention to the chord change will keep you gigging.
Scales
• Major Scale = R-2-3-4-5-6-7 Home base
• Major Pentatonic = R-2-3-5-6 Leave out the 4 & 7
• Natural Minor Scale = R-2-b3-4-5-b6-b7 Major scale with the 3, 6 & 7 flatted.
• Minor Pentatonic = R-b3-4-5-b7 Leave out the 2 & 6.
• Blues = R-b3-4-b5-5-b7 Minor pentatonic with the blue note b5 added.
• Harmonic Minor Scale = R-2-b3-4-5-b6-7 Natural minor with a natural 7.
• Melodic Minor Scale = R-2-b3-4-5-6-7 Major scale with a b3.
Let the major scale be your home base then change a few notes and you have something different. No need to memorize a zillion patterns. Let the major scale pattern be your go to pattern - then adapt/adjust from there.
Major modes
• Ionian same as the Major Scale.
• Lydian use the major scale and sharp the 4 - yes, it’s that simple.
• Mixolydian use the major scale and flat the 7. Change one note.....
Minor Modes
• Aeolian same as the Natural Minor scale.
• Dorian use the Natural Minor scale and sharp the b6 back to a natural 6. Change one note.
• Phrygian use the Natural Minor scale and flat the 2. Again change one note.
• Locrian use the Natural Minor scale and flat the 2 and the 5. OK here you have to change two notes.
Modal Harmony - the rest of the story.
• If you play your modes over a chord progression you will probably only hear the tonal center of your progression.
• However, if you play your modes over a modal vamp the vamp will sustain the modal mood long enough for the modal mood to be heard. The modal vamp droning effect will sustain the modal mood. Where with a chord progression the chords change so quickly that the modal mood does not have time to develop. Modal vamps of one to two chords let the modal mood be heard.
http://www.riddleworks.com/modalharm3.html
Scales and modes are for the melody - your solo. Chord tones are for your accompaniment bass line. Of course that's IMHO. To solo let the melody be your guide. Yep, melody has to be in there some place. Counting on running a scale or a mode and letting that be your lead solo - good luck. The song's tune is the foundation for your solo or your improvisation of that tune. Let the melody be your guide. OK easy said, hard to do. As the melody and the chord line to harmonize must share some of the same notes at the same time in the song -- and as the songwriter has already taken all that into account - inserting the harmonizing chord where needed - it makes since to play the chord's pentatonic scale over the chord - as that scale will have three chord tones and two safe passing notes in it's makeup. Play the chord's pentatonic scale notes over the chord changes as your melody solo right at first. Major chord - major pentatonic R-2-3-5-6 and minor chord - minor pentatonic R-b3-4-5-b7. Mix the notes up, no need to just run them in scale order. Think generic licks made from pentatonic notes and move those licks around with the chord changes.
Hal Galper's Master Class - Musical Vocabulary - YouTube R-3-5-3-6 8-5-R or 3-5-8-8-6-5-3-R. Make up some that sound good to you. Twenty licks used a hundred ways......
Generic Notes - for your bass line.
• The root, five and eight are generic and fit most any chord. Remember the diminished has a flatted 5.
• The 3 is generic to all major chords. So R-3-5-3 will fit under any major chord.
• The b3 is generic to all minor chords. And R-b3-5-8 will fit under any minor chord. Why the 8? Well the 8 is just another root in the next octave.
• The 7 is generic to all maj7 chords. Yep, R-3-5-7 fits nicely.
• The b7 is generic to all dominant seventh and minor seventh chords. G7 = R-3-5-b7 or Gm7 = R-b3-5-b7.
• The 6 is neutral and adds color, help yourself to 6’s. Love the sound of R-3-5-6 with a major chord.
• The 2 and 4 make good passing notes. Don’t linger on them or stop on them, keep them passing.
• In making your bass line help yourself to those notes, just use them correctly.
• Roots, fives, eights and the correct 3 & 7 will play a lot of bass.
Listen to what is said in these videos;
Hal Galper's Master Class - Technique, Part 2 - YouTube
Peace Piece (Bill Evans) - solo jazz piano - YouTube