| The problem of tracking (estimating) the pitch of a bass guitar is the most difficult part of the process- bass notes have such long wavelengths that it requires extremely fast processing. It has to interpret a partial wavelength as a complete one sometimes, and it has to fix on the incoming signal for at least half a cycle without becoming confused. Even if it can read very quickly, if the processor can't "think" accurately about what to do when the wavelengths are so long, with amplitude far below the readable envelope for such a long part of the cycle, then it will start spitting out incorrect pitches, or making a warbling or glitching sound.
Digital synthesis is easy with only a theoretical understanding, you can follow a recipe in a textbook with no problem. But the tracking issue is not so easy, and I would be surprised if any of the more successful formulations/designs are available to the public to read. | 
