Starting with a typical rock chord progression Figure A let’s turn it into 7/8 and see how it can work from a bass perspective.
Figure B now changes the time signature to 7/8, meaning seven quavers per bar. Let’s play it super straight as a starting point, playing every beat of the bar (quavers).
Counting each beat 1, 2, 3, 4 ,5 ,6, 7 (making sure to use ‘sev’ for seven as it’s just one syllable) it can feel quite similar to 4/4 (or two bars of 4/4) but just dropping the last beat. It feels like it changes early but can still really groove. A bar of 7/8 in this feel is often counted as four beats and then three beats in that fashion (1, 2, 3, 4, 1, 2, 3) feeling like 4/4 with the second bar just dropping a beat.
Moving onto something more rhythmic in Figure C, try to still keep the full count in your head/out loud/with your foot to lock it in. The first note in the bar falls on the 1 and is held for three quavers. The next two notes fall on beats 4 and 6.
Try creating your own and lock them in with a metronome/drum machine. To get wacky just take Figure B and randomly delete notes. Then test yourself by increasing the tempo, making it easy to come up with cool ideas.
Figure D uses more syncopation and semi quavers to push your skills even further. Remember that these examples are written in 7/8, meaning seven quavers per bar (but you count each quaver, so – 1, 2, 3, 4, 5, 6, 7). When you have semi quavers they are worth half a beat each – e.g 1 +, 2 +, 3 +, 4 +, 5 +, 6 +, 7 +. As always, start slow and get used to counting and feeling the time signature and rhythms before you ramp up the tempo. Next try changing the notes, key chord changes, etc to really stretch out. Figure D could be a great unison riff when locking in with the bass drum and snare or doubled with guitar.
As mentioned there are lots of examples of 7 (both 7/4 and 7/8) in rock, jazz, fusion, metal and more. Meshuggah, Weather Report, Chick Corea, Sting, Animals as Leaders are definitely worth a listen (plus loads more). 7 can be cool to create syncopated, more out-sounding rhythms but can also really groove – get stuck into it!