Some instruments (for example the guitar, the bass guitar, and the xylophone) have written music in a typical clef, however the note written and the note played are an octave lower or higher depending on the instrument. There are octave clefs that can be used in place of having an instrument transpose by octave, but are typically not used. Is there a reason why transposing by octave is more preferable then using an octave clef?
In practice there is little difference between using an octave clef and a normal clef for these "octave-transposing" instruments. An instrumentalist playing these instruments need not even think about the fact that the music sounds in a different octave to that written; although, of course, players and composers/arrangers should know that the sounding pitch is different to the written pitch. The octave clef simply makes explicit what is implicit to instrumentalists and composers/arrangers.
If, on the other hand, you are asking about why these instruments use octave transposition at all, it is usually for one of three reasons:
- if the instrument has quite an "extreme" range, it makes sense to use an octave transposition rather than have most of that instrument's range require many ledger lines. (Piccolo and Bass Guitar are good examples: the lowest octave of the Bass Guitar range would go down to four ledger lines below the bass clef, and this is just for 4-string bass!; the Piccolo would be written from the D on the treble clef upwards to many, many ledger lines above the stave.)
- to allow an instrument to use the same fingerings as another similar instrument. For instance, Bb Bass Clarinet would easily fit within the range of the bass clef, but by having it sound an octave lower on the treble clef, it has the same fingerings as Bb Clarinet.
- to have a "best-compromise". For instance, the guitar has a written range from three ledger lines below the treble clef to approximately five ledger lines above (depending upon type of guitar and use of the highest register). If this were notated at sounding pitch in the bass clef, it would only have it's lowest note one ledger line below the bass clef, but would need to use many, many ledger lines above the bass clef for the highest register, or would have to frequently change to treble clef (which would be difficult as guitar music has all pitches notated on a single clef simultaneously).
Either way, this is simply a practical shift of pitch used to allow music to be notated most easily on a particular stave, without using lots of ledger lines; it isn't as significant in practice as non-octave transpositions.
Just as a final note: I have seen intriguing examples of guitar music written at sounding pitch, on dual treble and bass clefs, in the same way as piano music. One well known example is the orchestral Electric Guitar part for Stockhausen's Gruppen for Three Orchestras.
I think a direct answer to "Why call the instrument transposing?" is: Because if you read a note that is written A (440) and when you play it, it sounds A (220) then by definition, you are transposing. People commonly hold the misconception that transposition has to be from one letter name to another. It is not required that the letter name change, only the pitch. Although reading a middle C and sounding the note a major second below at Bb would be considered transposing, reading middle C and sounding C on the second space of the bass clef is also transposing.
The original question of "Why are there transposing instruments that transpose by octave?" could probably best be answered with: A goal of all music notation is to make the notation easy for the performer to read and perform. If, by transposing an octave, more of the notes involved in a given part can be placed on the lines and spaces of a staff as opposed to on ledger lines above or below it, then it is considered a "good" notational decision and should be done. Over time, de facto standards have kicked in and a given instrumentalist has become accustomed to seeing parts that are transposed, and would likely prefer that they be that way, although there are lots of examples of written parts (for trumpet, flute, and other high register instruments) that are notated on the staff with a notation to transpose up 8va.
It's down to the range of the instrument compared with the range of the clefs. With guitar, the lowest note is traditionally an E. This E would come on the 1st ledger line below the bass clef. Putting the open top string on the treble clef stave,bottom line. That's before we go to the rest of the notes up that string. Playing on two staves isn't easy (ask a pianist !), so it makes sense to use just the treble clef as then the lowest note is only 3 ledger lines down,(just under) and this gives headroom for more of the higher notes. Yes, it's an octave out, shown usually by the little '8' by the clef sign, but guitarists don't think about it much, if at all. This makes the guitar a transposing instrument, which happily uses an ordinary,better-known clef, without having to resort to an alto or tenor clef, which could put everything in a good place, but folks are more familiar with the standard treble clef stave.
The octave clef, with a low '8' should be used, and on quality music, is. However, guitarists just become programmed, and 'know' where to go.
Actually, I've just looked through some of my library - of classical through to contemporary - and there are only a few with that octave clef.Yes, we must just have got used to it !!
Not at all sure whether this answers your question...
Actually I think that at least in one respect your question starts at the wrong end: this is no property of the instrument, but a convention of how it is notated. Double bass and contrabassoon sound an octave lower than they are notated. The notation is already in the bass clef, so while one could use ( impracticable many ledger lines or) a transposing clef, it is clear for any player as it is. I have never seen a down- transposing tenor clef which would be appropriate for the high register. Same applies in the other direction for piccolo flute.
This leaves the transposing clefs available for further extremes (technically impossible for lower direction of contrabasson, unsure about higher direction of piccolo).
Piccolo COULD be notated with an 8-up treble clef, double bass and tuba with an 8-down bass clef. (That is not an exhaustive list of octave-transposing instruments, but it'll do for now.) We traditionally choose not to.
You want a 'why'? Well, cello and double bass, bass trombone and tuba, often shared a musical line. A typical Romantic era bass trombone/tuba part would have been single-stave, with perhaps occasional 'trombone only' or (less frequently) 'tuba only' passages. Cello and double bass became independent rather earlier, but a Baroque basso continuo part might have been played by any available bass instruments, some sounding an octave lower than others. The players were accustomed to reading a straight bass clef in ensemble. No point in pedantically adding the 8-down at other times. But I readily admit that's a weak argument. The main reason we don't use the 8-clefs is tradition and usage.
Tenor voice, when written in treble clef, always uses the 8-down treble clef. Despite this, it's quite confusing to read a 4-stave choral score where the tenor line LOOKS higher than the alto. We can't blame this on ancient tradition - all voices originally used their own position of the C-clef.
The question asks 'Is there a reason why transposing by octave is more preferable then using an octave clef?' This is a bit misleading. In performance, no-one's transposing anything. The player reads their accustomed notation, the fact that their sound is an octave different isn't a practical issue.