MUSICAL INSTRUMENTS — RICHARDSON 255 



oboe and the clarinet each sounding A have then different spectra 

 and organ pipes have different wave form (pi. 1, fig. 2) and can thus 

 be distinguished. But this distinction is often uncertain between 

 two instruments at certain parts of the scale, so that, for example, 

 the violin steady tone is very like that of the oboe. Yet many people 

 can distinguish a violin solo from an oboe solo. 



How then does this happen? One factor is that the timbre of an 

 instrument is not constant over the whole of its range, so that the 

 quality just cited is unlikely to persist when the soloist passes from a 

 note of medium pitch to one higher or lower. Another is the difference 

 between different instruments in the starting and in the buildup of 

 steady notes, in the scrape of the bow, and in the tonguing of the reed, 

 etc. The first of these characteristics is called formant, the second 

 transient, though sometimes the first word is used to cover both. The 

 removal of the transients can make a great difference to the ease of 

 distinguishing between the instruments of different, or even the same 

 types. 



The formant, in the narrower sense of the word which I prefer, is 

 that feature in the sound of an instrument (or of a voice) which clis- 

 tinguishes it from another of the same breed and is largely a question 

 of the existence of resonances which may be excited in the soundboard 

 or box to which the primary tone producer, vibrating string, reed, etc., 

 is coupled. In speaking of "soundboard" one must use the word in 

 the wide sense to include all neighboring bodies which can be set in 

 forced vibration. For instance it ought to include the cavity resona- 

 tor formed by the player's lungs, whether he is playing oboe or violin ! 



Another factor which must be considered is the directional char- 

 acteristic. An instrument with a definite soundboard like the violin 

 probably radiates best in the direction perpendicular of the board, a 

 wind instrument in the direction of the bell, though this direction may 

 be changed by local reflecting surfaces. 



The soundboard should vibrate as a whole up to as high a pitch as 

 possible. If it tends to subdivide into segments — some moving out 

 while others move in — their mutual effects at a distance will cancel 

 each other and the sound will not radiate well. 



This directivity is only, however, valid for high pitch. At low 

 frequencies it fails and the sound spreads equally in front of the 

 player. (Physically this is the same factor that intervenes when 

 sound passes through a doorway; high-pitched sounds pass mainly 

 straight ahead in a beam, but low-pitched sounds spread round a 

 corner.) This is a matter of some importance when one wishes to 

 localize the sound from a particular instrument in the orchestra — 

 for instance, a good violin, in the sense of one which, if used for the 

 solo part in a concerto, will stand out from the mass of other strings. 



