They both have very different postures that have nothing in common. The positioning indicators for intonation on a double bass are very different from that a bass guitar. The scale length is different. Posture alone isn't going to do it. And apart from frequencies, playing those two instruments is completely different. It's got nothing to do with electric bass intonation, it is a false equivalence.
Violin, cello, and double bass also have string lengths, playing postures and playing techniques that are very different from each other. Yet, the
principle underlying correct intonation is the same: ear training, rigorous left hand technique, and muscle memory. So the argument quoted above is only superficial and not really convincing.
I strongly believe that although the string length, the playing posture, and the instrument shape of the fretless BG are very different from those of violin, cello, and DB, the
principle for correct intonation remain the same.
The apparent similarity between the fretted and the fretless BG is deceiving: although the instrument shape, the playing posture, and the right hand technique are identical, they are really
different instruments with respect to intonation, and left hand technique (more about this below).
With respect to intonation, the fretted BG is essentially similar to the piano: intonation is built in by construction, and there is no compelling need to press down the string at an exact position. This range of tolerance is at the core of the 1-2-3-4 left hand technique: with the hand being stretched, the 1st and the 4th finger usually press the string in different places between 2 frets (the 1st finger typically plays very close to the fret, whereas the pinky frequently plays less close to the fret), especially in low end of the fingerboard, where spaces between successive frets are wide.
With respect to intonation, the fretless BG is actually closer to the violin family instruments and to singing: in order to play in tune, it is vital to:
1. be able to
pre-hear internally the note to be played
2. have a very solid and well-trained left hand muscle memory in order to finger the string at the right place to play the note that is pre-heard (and btw,
visual cues provide an essential assistance here - no one is denying the usfulness ot this!)
3. clearly hear the note actually played (in the context of what is being played by other musicians around) in order to check (and if necessary correct on the fly) the pitch of the note.
The apparent (and deceiving) similarity between the fretted BG and the fretless BG is a source of considerable frustration for bass players who want to try out playing the fretless bass, and
expect to be rapidly playing at a same level on fretless as on the fretted BG, without realizing that it is a
different instrument that needs to be learned on its own.
More specifically, what requires a specific training is the left hand technique: the 1-2-3-4 technique becomes problematic on the fretless, because the stretched hand shape (in particular close to the nut) usually does not allow to play in tune in a fixed position, and because tiredness would cause the hand to close at the expense of intonation. The 1-2-4 (or Simandl) technique borrowed from double bass is (in my view) better adapted for correct intonation on fretless BG, because the hand is in a relaxed shape and the notes can be played in tune without stretching the hand, in particular close to the (higher up on the fingerboard, 1-2-3-4 becomes quite manageable). (To be complete, one should point out that some players play 1-2-3-4 everywhere on the neck on fretless, and some do this even on the DB; but this requires to use a pivot technique that is somehow more advanced and anyhow requires a specific training as well).
A rigorous 1-2-4 technique enabling correct intonation on fretless BG (and on DB) rests on several elements:
1.
in-position playing: typical exercises involve playing within a fixed position in the context of some musical background (backing track, drone, etc.) that provides the reference for intonation. Ideally one should sing the line first, and then play it (to practice the pre-hearing).
For in-position playing, any visual assistance should really be unnecessay; if some player needs to watch his/her left hand in order to play in tune in a fixed position, I would consider this as a serious flaw that needs to be worked on.
2.
shift accuracy: this is a more tricky point, which most players transitioning for fretted BG would find challenging. On fretless orchestra instruments (violin, cello, DB), players devote a considerable amount of time practicing specific exercises aiming at training this difficult skills. Such exercises have to be progressive: 1/2-step shifts, then whole-step shifts, then minor-3rd shifts, etc... Noone should expect to nail accurately shifts of a 5th overnight. Here as well,
the ear should play the primary role, and intonation references provided by the musical context of other musicians, as well as by including open strings and harmonics in one's playing are essential. In a normal playing (performance) situation, those long shifts would naturally
benefit from the assistance provided by the vision, but it is really
worth practicing those without looking at the left hand because all the attention is then shifted to
the ear,
which is the ultimate judge for intonation.
3. in addition to the technical aspects mentioned above, using the 1-2-4 technique requires a
completely different fingering strategy, because the hand spans a whole step (instead of a minor 3rd for 1-2-3-4 technique). All the fingering patterns and "boxes" for scales and arpeggios BG players using 1-2-3-4 are familar with become useless (at least close to the nut). Instead, one can borrow fingering strategies from the DB, but, again, this is something that needs to be learned and practiced, and which does not come overnight. More importantly, this is conducive to some musically different type of playing, where shifting is much more prominent and has to take place in a very fluid manner.
These are my observations, as a player whose principal instrument is the double bass, and who has (almost) never tried to play a fretted BG. I would not be surprised, though, that a different musical path implies a different approach to the fretless BG. In particular, it is well possible that playing the fretless BG with 1-2-3-4 technique (for the reasons explained above) requires more visual assistance than when using 1-2-4 technique (for me, at least, it would).