I sometimes get asked “How do you manage to play a six string fretless bass?”, I usually reply “I don’t know really, I just do”. Most bass players normally start on a four-string fretted bass. My first bass was an Ibanez and the second was a Tokai. I then decided on a matching pair of Yamaha BB1100S four string basses, one was fretted and one was fretless, and that was it, my fretless career had begun. I have always liked the warm sound of the fretless as you could create slides not possible on a fretted bass. It’s great for playing blues too.
I now own a matching pair of six string Dean Edge basses one fretted
and one fretless, as shown above.
I also own an AXL Johnson Catalyst 6 string fretted bass as shown here.
However, this bass has now been converted to fretless by removing the frets.
The fret slots were then inlayed with wood, smoothed down, and the whole fingerboard was finally lacquered and polished - all done by my good friend and Luthier Harry Miller.
Obviously, the main difference between a fretted and fretless bass are the frets. But you have to be conscious where your finger is placed on these two styles of basses when playing them. On the fretted bass your finger can be placed anywhere between the frets, so the string, when pressed, passes over the next fret, and that determines the note. Conversely on a fretless bass, your finger needs to be positioned where the fret would normally be, as your finger in contact with the fingerboard determines the length of the string, and therefore the note. You also need to be accurate in the positioning on the string on the fingerboard, or the note can become sharp or flat, - even a slight rotation of the finger can create that.
However, the main issue is to get the fingers to feel and recognise the differing widths between the strings of a four-string bass, and the strings of a six-string bass. This in time becomes automatic (and is what is termed muscle-memory) as your fingers get used to it. You can see in the bass guitar example images below the fingerboard width, and the differing spacing between the strings, and although it doesn’t look much, it still makes quite a difference when playing. If I were to pick up a four-string bass, being so used to a six-string version, I probably would tend to 'miss-finger' a few of the strings here and there, until I got used to the wider spacing once again.
Typical 4 string bass
Typical 6 string bass