All musical tones are based on the harmonic series - whether it be a length of brass pipe, a church bell or a taut length of string, all instruments are subject to harmonics. The harmonic series are a sequence of pitches relating to a lower pitch (or fundamental note,as it is often called). Therefore a sound of a certain number of vibrations will also cause overtones to resonate in a ratio to that sound eg. a 100 Hz sound will be accompanied by overtones of 200, 300 and 400 Hz,and so on. All musical sounds possess all the notes of the harmonic series and it is the way these notes are blended together that gives sounds their individual ‘timbre’ or texture. Therefore the blend of the harmonic series in an oboe is different from that on a violin.

The harmonic series has been at the heart of tuning and temperament for thousands of years, before the standardisation of pitch into what we call ‘equal temperament’. This tuning system which has only gained universal currency in the last hundred years is the least understood of all musical concepts as it has been so wholly embraced. In so doing, not only has it ironed out music into 12 strictly equal semitones (robbing it of much of it’s harmonic character) but it also goes against the natural laws of the harmonic series. This is why even the world’s finest orchestras can have irreconcilable tuning issues.

For a full explanation of this all-encompassing musical dilemma I would like to heartily recommend Ross W. Duffin’s ‘How Equal Temperament Ruined Harmony (and Why You Should Care). An organist friend of mine passionate about various tuning systems brought it to my attention it and it is scholarly, concise and a hugely entertaining read.

On all stringed istruments the harmonic series reveals itself as described above. Therefore when a string is foreshortened (or ’stopped’) by a finger the same ratios apply eg. there is a harmonic exactly half way up each string (ratio 2:1) sounding an octave above the open string. The second one is a fifth higher than that (ratio 3:2) and so on. These notes are called harmonics and can be played by touching the left hand finger very gently on the string with a fast and light bow speed (in a similar way to making a wine glass produce a pitch by running one’s finger along the rim of the glass). The note thus produced is pure, clear with a flute-like quality different from any non-harmonic notes.

Stringed instruments are also capable of producing ‘artificial’ harmonics. These mimic the tonal qualities of a harmonic but produce notes of a higher pitch than the natural note in the same way. The lower finger ’stops’ a note in the conventional way with a higher finger gently touching the string at the interval of a fourth above to produce a note two octaves higher than the lower finger. In this manner, it is possible to play whole melodies transforming the sound of the instrument into a completely different timbre.

In the context of a string arrangement, harmonics can produce an ‘other worldly’, ‘eerie’ quality that can add a real sense of mystery and magic to a piece, even when mixed in with other instruments in a track, the effect is haunting!