Harmonics on the oboe - Christopher Redgate 2018 (c)
A wide range of harmonics are available on the oboe, in fact oboists use harmonics as part of their standard performing practices.
Harmonics are obtained by suppressing the fundamental and causing a higher pitch to sound—for simplicity I will call these higher sounds harmonics—this suppression takes place, usually, by modifying the fingering of the fundamental, though occasionally it can be done with the embouchure alone. On the oboe, cor anglais etc. this is normally done by using the octave keys or by lifting or rolling the first finger (index finger) of the left hand. This key has a small hole in it for this purpose. Therefore any pitch in the second register and above is a harmonic, though of course they are not noted as such in scores.
Oboists, traditionally, have only used a small set of fingerings which they correctly refer to as harmonics. Technically these are third harmonics and they run from F at the top of the treble clef to the C at the top of the treble clef. They produce a slightly different, and usually quieter, sound than the standard fingering at this point and are often used by oboists in order to produce a muted pitch.
These third harmonic fingerings can also be found in ‘bisbigliandi’ in contemporary scores.
These third harmonics are produced by fingering pitches from bottom Bb to bottom F and using either the first or second octave key in order to force the upper harmonic to sound. These are very effective and easy to produce.
However, the oboe has a wide range of other harmonics which are rarely used:
From bottom Bb up to the concert A no harmonics are possible because these are the fundamentals. Middle Bb, B and C can all be produced as second harmonics, usually by venting either the first or second fingers of the left hand. These are slightly awkward fingerings and should used with care and usually in slow passages; a bisbigliando cannot be obtained using these fingerings.
From C# in the middle of the staff up to C at the top of the staff other second harmonic fingerings can be found usually by using one of the octave keys or by venting the standard fingering in unusual ways—a performer wishing to use these should experiment and see what can be found.
From the C# at the top of the staff upwards, in normal performance, these pitches are already third, fourth or occasionally fifth harmonics, however, by experimentation the performer will find that using the lowest fingerings on the instrument and experimenting with the octave keys (sometimes using more than one at once), the index finger of the left hand and occasionally half or quarter holing other keys—and sometimes increasing embouchure and/or breath pressure—a range of third, fourth, fifth or sixth harmonics can be found. It should be noted that some of these harmonics will not be very well in tune because of the complex fingerings and of course the fifth and seventh harmonics are acoustically out of tune! These fingerings are very cumbersome and complex and should only be used in slow passages or in isolation. They do however create some very interesting sounds.
On many occasions another option can be used and that is the alternative fingering or modified fingerings especially where a colour trill, or bisbigliando is required or where they are required in fast passages.
All of these principles should also work on the other instruments of the oboe family within the obvious limitations of each specific instrument.