C - D/C - Fm/C - C
This kind of fixed bass, isn’t it called ostinato?
Is there a pattern or where it’s used. Or do you just rely on your ears?
If you use a normal bass, that’s fine.
But I see some songs that like to become a constant bass, why on earth?
Ostinato is a repeated phrase / motif, and isn’t associated with any particular pattern.
Basso Ostinato (sometimes called ‘ground bass’) is such a pattern played by an instrument in a low register. Historically, it would would provide a rhythmic underpinning in a quartet / small group of musicians.
That said, it doesn’t matter if you don’t use the same bass.
If you want to use persistent bass, that’s fine, right?
It will only affect the atmosphere of the music, but it will not affect the singing. Did you, now?
Keeping the same note in the bass like that is usually referred to as a pedal tone.