How the names work, and why.
This is a tricky subject, the reasons why are "historical", the result of centuries of development of instruments and musical taste. I will do my best to explain the intricacies and seeming illogicalities.
With woodwind the concept of an instrument being "in a key" is not helpful. Put it out of your mind for the time being.
The way instruments are described depends on the instrument. This is not a problem if you know how the instrument works but it can be a major stumbling block. Orchestral instruments (including the recorder) are treated one way, and "folk" instruments (including the "penny whistle") are treated another.
Because it is common for a woodwind player to play more than one instrument there are great advantages in linking the notation to the fingering. The notes which are fingered the same way on most woodwind instruments are B, A, G, E and D. (I will come to the treble recorder, clarinet and bassoon later.) Of these notes the one to pick out is D, the lowest, often the lowest playable note. This note is played with six fingers and is written just below the treble stave, regardless of the octave at which the instrument sounds. To the player, the note is always thought of as a D, and when the instrument is non-transposing, it really is a D. Orchestral instruments have a seventh hole. You close it to play the note C. Those orchestral instruments which do not transpose are referred to as C instruments.
With most natural objects size varies, and size matters. Musical instruments are no exception. There are optimum sizes that provide the right balance of tone colour and range of notes. There is much more at stake than the ability to produce any given note. Listen to the bassoon at the start of Stravinsky's Rite of Spring. The notes are well up into the flute register, but a flute would not convey the sense of unease and mystery, even anxiety. The bassoonist is approaching the summit of Everest without oxygen. I have heard it said that present day bassoonists are getting so good that the music ought to be moved up a tone every decade so that the audience can share the player's apprehension.
If one could choose instrument sizes that were an octave apart all would be well. Life and nature, however, do not work like that. We have ended up with strange sizes. Playing them is not a problem, it is only the writing down of the music that gives trouble.
Let us take, for example, the clarinet. The standard instrument sounds a whole tone lower than would a piano being played from the same written music. The clarinet is a developed orchestral instrument capable of being played in all keys. The convention is to describe such instruments in terms of the note which is heard when the player reads and plays what he thinks of as a C. So, that clarinet is referred to as a B flat (Bb) clarinet. The arranger needs to write the music a whole tone higher on paper than the sound he wants to hear. In order to hear a C the arranger must write a D if the music, as written, will be played on a Bb clarinet. There are many sizes of clarinet, both larger and smaller. There is even a C clarinet, which is not popular, despite the ease with which can play normal music. And the reason? The sound. The C clarinet is too small, not enough "body", and at the same time too big, not enough brilliance. When orchestral players meet parts written for it (not uncommon in early classics) they use their Bb (or A) instruments and finger notes a tone (or three semitones) above what is written, transposing as they go. This is not so difficult as it sounds, especially after practice.
"Folk" instruments are named differently. They generally have D as the lowest note and do not play well in some keys. (It is the note F natural which causes the greatest trouble. May I remind you? In D major, the scale includes F sharp and C sharp.) With six finger holes and a lowest note of D it is not surprising that they play the scale of D with the greatest ease. Because of this they are named after the sound of the written six finger note (D).
This is how it is that the D whistle and the descant recorder (often referred to as the C descant recorder) produce the same pitched sounds when playing from the same line of music. If a whistle player needs to play from music intended for Bb clarinet the C whistle is the most obvious choice. (You may need to think about this, I have double checked the text, and it is correct!)
If you are still with me, now is the time to think about "key". This only really relates to "folk" instruments. Anyone who has studied an orchestral woodwind instrument will have been obliged to learn scales, in all keys major and minor, together with chromatic and whole tone. Some are more difficult than others but nothing is impossible and a "key" is a mechanical part of the instrument, or the mode of the music. The instrument itself has no intrinsic "key", any more than does a piano.
With the "folk" instruments it is different. It is not possible to move far from the home key of the instrument, and, fortunately, not generally necessary. Most folk music is notated in D and rolls off the D whistle and six hole flute with ease. C natural is hardly a problem and G sharp isn't either, so you can play in G, D and A major without trouble. You don't need a G whistle to play in G or an A whistle to play in A. When it comes to F major, an F whistle might be the thing, but it would probably be too big, or too small, so the C whistle is the usual choice. (This is another place to pause and think it through!)
The term "concert pitch" is used for the actual sound. This is what the listener hears, and the notes he would pick out on a piano if he were to join in. The score (that is, the written music showing all the parts for the instruments on one page, as used by the conductor) may show either the concert pitch or the written pitch for each instrument. It is a foolish conductor who has not checked this out before the rehearsal.
Treble (also sopranino and bass etc.) recorders and bassoons do not fit the six finger or seven finger explanation above. Their size has always been so "right" that they have been a law unto themselves and have been notated for a seven finger F, giving rise to the notion that the treble (alto) recorder is "in F". Indeed, some early modern editions of recorder music are published with a part for "F Recorder" (treble, fingered as descant). I know one expert flute player who is a very passable recorder player too, but re-writes the treble recorder part as if for descant, for safety, in public performance. It is not the thing to do, but it works.
Clarinets are interesting. They produce a second register that is one and a half octaves above the first. Even playing the second register down the tube to an eighth finger hole (both little fingers) does not enable you to link up with the first without extra holes above the thumb hole. The second register seven hole note is written as C in the stave. The first register seven hole note is F below the stave. So, the clarinet behaves as a C type instrument up high, and an F type instrument down low. Recorder players feel quite at home with this however odd it may seem if you are unfamiliar with the recorder.
There are a few instruments whose odd size is a matter of utility. The Db flute is one. Before the late C19 flutes were not fully chromatic and were extremely difficult to play in some flat keys. In a military band, dominated by families of clarinets, saxophones, and brass, all made in flat keys, playing happily in what they think of as F, for example, and sounding Eb, concert, the flutes had a hard time. The problem was solved by making flutes a semitone smaller, putting their pitch up to Db. (In folk parlance it would be Eb.) The written music then has to be a semi-tone down. The Db flute players were very happy to get away from the flat key and into something which suited their instrument well. With modern flutes there is less need, though I have a Db piccolo only about 40 years old and a military flute from 1900's. They are a bit small and the tone quality is nothing to get excited about.
John Everingham 7th. November 2004