but i'm just curious to know what they are for? a bit more descriptive that "different" what do they do that a fretted can't or visa versa?
I kind of want to invent new scales with 18 notes to the octave... which is why i want no frets to get in the way of it... but i'm pretty sure that's not their intended purpose?
Just to give a quick background, I played fretted bass for about 4 years mostly on Fender Jazz Basses, before trying out and buying a Warwick Corvette Fretless. I've been playing both fretted and fretless about 6 years since then.
First of all, to respond to what you said earlier, you definitely don't want to invent new scales with 18 notes to the octave (unless you're playing middle eastern music or something) You'll just sound like you're playing out of tune, which is always bad. You should stick to playing notes that are in the normal western chromatic scale. Maybe, foray into quarter steps, etc. when you become more experienced and are ready to experiment, but I haven't had any success with that personally.
The first thing to note is that you need to be very precise when fingering notes. Just a little bit off the mark and you'll sound pretty bad. You should use an accurate chromatic tuner to practice making sure your notes are exactly in tune when you practice. Some fretboards come with lines to guide you whilst others have only the dots on the top. I would recommend an unlined fretboard, because you don't want to become dependent on your sight to look for notes, you need to train your ear. The top dots are a useful reference for when you have to change hand positions quickly, but other than that, I rarely look at them. Also, you'll just look cooler and more competent with an unlined fretboard.
In terms of the differences, A fretless bass tends to give off a warmer, "woodier" sound when playing than a fretted. This is due to the fact that the string is pressed against the wood fingerboard and your finger to make a note rather than a metal fret. It sounds closer to an upright bass, but still not quite there. The only way to get that sound is from an upright! Some players, myself included have found that after getting used to the fretless, you can actually play FASTER. You don't have to worry about frets, so you can make the action lower and not worry about buzzing. Some people find it difficult to learn, while others can pick it up almost immediately and play.
Some techniques are different as well. String bends have virtually no effect, so you have to slide your finger slightly up the neck while fingering a note to achieve the same effect instead. You can also make better use of vibrato, where you rapidly move your finger a slight distance back and forth. Watch a video of a violinist to see what I mean. Other than that, slides are definitely smoother, and I use them much more often when playing fretless.
In terms of when it can be used, it's all up to you. I've personally found the sound to be pretty much worthless for classic rock, blues rock, hard rock etc. but very useful for Jazz, Jazz Fusion, Funk, etc. or when you want to get an upright-like sound without dragging one of those behemoths around.
So in conclusion, I recommend you gain some experience with the fretted bass before you buy a fretless. Definitely try some out at the store in the mean time though. When you are ready to step up to the fretless, make sure you use flatwound strings. Round wounds will tear up your fretboard. I HIGHLY recommend Tomastik-Infield JF 344 flatwound strings. They are very expensive, but they will last forever, and the tone is unbeatable in my opinion. Hope this helps you out and good luck!
Just try one out and see if it sounds or feels appealing to you. Not a big deal.
