Arguments rage, tempers fly, and every bass guitar player has at least some opinion. Around the world, they ponder the question: 'When does a song's style or feel make it most efficacious to use a fretless bass, instead of the standard fretted bass?' Well seek no further, for here you will find the questions to all your answers, and hopefully emerge with at least confusion, if not clarity.
Differences between the Instruments
For those Researchers not familiar with fretted and fretless basses, there is only one fundamental difference. Fretted bass guitars have metal frets up the neck of the bass, like standard guitars, whereas fretless bass guitars have a smooth fingerboard, like double basses. All other factors, including the body shape, electronics, and string tuning are identical on both instruments. Both instruments can be played either with plectrum (or 'pick', in America) or without, although it is slightly less common to play a fretless with a plectrum than it is for a fretted.
The Advantages of the Fretted Bass
The most prominent advantage that the fretted bass has over the fretless is that, quite simply, it is vastly easier to play. The smooth fingerboard on a fretless means that the player's fingers are the only factor determining the length of string that is vibrating, and thus the note being played. Since the fingers can be placed anywhere along the fingerboard, this introduces the possibility of intonational errors. On a fretted bass, the string always stops vibrating at a fret, creating a note perfectly in tune (on a perfectly tuned and adjusted bass).
Additionally, on a fretless bass, the player must apply more finger pressure than on a fretted bass. On a fretless, the left-hand fingers must exert enough pressure for the string to maintain constant contact with fingerboard. On a fretted bass the fingers must simply exert the pressure necessary for holding the string against the raised metal fret, far less than is needed on a fretless.
Consequently, strings of very fast notes, especially through large or strange intervals, are infinitely easier on a fretted bass, while they can easily become 'muddled' on a fretless bass. For example, the opening bass-line for the Red Hot Chili Peppers' song 'Around the World' simply would not work correctly on a fretless. Even if the player were skilled enough to play each note up to speed, which would be an impressive feat in of itself, the clarity in each note would be lost.
The Advantages of the Fretless Bass
The only purely stylistic advantage the fretless bass has over the fretted lies in the fact that the absence of frets on a fretless allows a smooth glissando, or slide, from one note to another, which is not possible with a fretted bass. In other words, on a fretted bass one must play, for instance, either an 'E' or an 'F'. However, on a fretless bass, it is also possible to play every pitch between that of an 'E' and an 'F', allowing the player much more musical freedom, but, as mentioned earlier, leaving the need for proper intonation.
This ability also allows the skilled bass player to compensate mid-song for bad tuning. For instance, an experienced player could realise that his/her 'E' string was flat, and for the rest of the song play all notes on the 'E' string slightly sharper than usual, resulting in on-tune notes despite an off-tune bass.
The most noticeable difference between fretted and fretless basses lies in their tonal qualities1. Fretless basses, since they are intoned by the fingers, have a much smoother sound than fretted basses. With less of an attack, and an overall tone with much less upper and midrange, sounds from fretless basses tend to sound less like a string being plucked, and more like a sound very rich in low-range frequencies that simply starts at one moment and ends at another.
The fretted bass, on the other hand, tends to have a sharper, crisper tone that is often richer in harmonics than a fretless. The difference between the two could, to anybody familiar with bass playing, be described as similar to the difference between playing a bass without a plectrum and playing the same bass with a plectrum. That is, the change in tone from a fretted to fretless bass is comparable to the change in tone from a plectrumed note to a non-plectrumed note.
So, When Do You Use a Fretless?
Ultimately, the matter of when to use a fretless bass, or whether to use one at all, is an individual's choice which grows from the sound he/she requires for any given song. Bass-lines such as the one in The Beatles' 'With a Little Help From My Friends' would suffer severely with a fretted bass, while ones such as the bass-line used in 'Drive My Car' would be next-to impossible with a fretless.