"Favourite Keys" on Orchestral Instruments

Certain instruments in the orchestra have a preference for certain key signatures which either sound particularly good on these instruments or are easy to read and therefore have a lower stress factor when sight reading which allows to concentrate more on other elements of the music.

Unfortunately, depending on instrument or section, these keys don't line up too well so it is often an either/or decision.

Strings:

You will get the most resonant sound on strings if the at the time "unused" open strings create some sympathetic resonance with the tones that are being played which means that playing an actual note on one string will if it has the right pitch induce a resonance in the other strings and create a more substantial sound. G, D and A are open strings on Violins, Violas and Celli so any key with a strong emphasize on these notes (and their harmonics) will sound particularly good in the string section which naturally would be the major or relative minor keys of these notes.

Brass:

The fundamental that most brass instruments will create if you don't press any valve or have the slide completely in (Trombones) will either be F (Tuba) or Bb (Trombones, Trumpets) or F and Bb (Horns using the so called "Double Horn"). As you might know, the resulting harmonic scale on these instruments will include most of the notes of the major scales based on these notes pretty "early" in their harmonic scale. Of course it is possible to play in all other keys by using the valves or slides but the more "diversion" the sound needs to take through artificial extensions like valves the more inconvenient it will be for the player which will have an impact on the quality of the produced tone. If the function of valves is not entirely clear to you just take my word for it and wait for a later post where I explain their function but if you know how they work here is the nerdy explanation: The problem with valves is that they don't work identical over the entire range. The lower you go the more "extra tubing" you need to get to the actual pitch you want. This goes as far as the Tuba using an extra "small slide" additionally to the valves that allows to compensate for that problem in the very low register. But also for the other brass players this issue is a common problem. You have a certain range to bend a tone up or down (usually at max a semitone) by changing your embouchure which is used to pitch compensate for the varying effects of the valves depending on where in the range you use them. This compensation comes at the cost of sacrificing some of the purity of the tone as well as it will cause intonation to not be as pure. So long story short, the first few flat keys (F, Bb and Eb major) sound best on brass as they require the least alteration of the tubing length by use of valves or slides.

Woodwinds:

Woodwinds are in fact the most flexible ones regarding keys however they come with one exception (which also applies for Trumpets). As Clarinets are transposing instruments in Bb it means that you need to write a whole tone higher for them in order to get the desired pitch. A passage that is supposed to sound in C major on Clarinets needs to be written in D major a whole tone higher. From the key signature standpoint that adds two sharps for them. If your piece is already written in a "very sharp" key signature (e.g. B major with 5 sharps) this will add even more sharps for the Clarinets at a very inconvenient C# major with 7 sharps. Sightreading such a thing is very inconvenient. In such cases, Clarinet players often like to switch (without asking) to Clarinets in A which transpose a minor third making a sounding B major into a playing D major (losing 3 sharps). Usually this is even done without needing to give them a new part as they figure the transposition change out on their own. And the more convenience they get through using this different instrument still outweighs the hassle that comes with transposing the part in their head.

So as you see, the choice of key is not only based on "what you like" but should rather be based on what sounds best. Unfortunately the favourite keys of Brass and Strings seems to contradict each other so you need to make a conscious decision on who to favour.

Two great examples are (as often) to be seen in the work of John Williams. The brass heavy Main Theme for STAR WARS is written in Bb major which sounds excellent on brass, however the string heavy high soaring Main Theme for E.T. is written in D major, favouring the strings and their resonance. These are two excellent examples of conscious decisions for a certain key signature to maximize the desired effect.