The more guitar ancestors were impelled, in some spheres of play, towards the duplication of composed vocal and polyphonic textures during the later fifteenth century – a process continuing in the sixteenth – the more it became essential, in the judgement of many, for the fourth course of the guitar to include at least one low-octave string, or bourdon, to provide extra capacity for grammatical counterpoint. This is made clear in the earliest printed music for the guitar, prepared by Alonso Mudarra in 1546. Mudarra provided a note that the player should have a low-octave string or bordón on the fourth course. This implies that Mudarra expected there would also be a higher-octave string in the pair, since he speaks of bordón in the singular, and further implies that some guitars had no bourdon at all – hence the need for a preliminary warning – but only a pair of strings at the higher octave. In 1555, Bermudo confirmed that musicians ‘are accustomed to put’ (suelen poner) a higher-octave string on the fourth course of the guitarra, ‘which they call requinta’ (Declaracion, Book IV, Ch. 39).

This disposition, with an octave pair for the fourth course, bears directly upon the sound-picture of any music for which it is deployed, especially if the higher string is placed in an ‘outside’ position, rather than ‘inside’, and is therefore the first to be struck by the thumb. When the high-octave string is placed on the inside it may receive only a light skim of the thumb, or may even remain untouched, if the instrument is not carefully set up, since the higher string is necessarily much thinner than its neighbour. An octave string placed outside, however, produces an intermittent scintilla of sound, or glitter of high harmonics, as the texture variously commandeers or releases the fourth course. This effect, heard as a colouristic device, and as a means to lend high harmonics to the duller sound of the thickest gut string on the instrument, was apparently welcome even to such an exacting contrapuntalist of the mid-sixteenth century as Mudarra.

Special difficulties, notably with regard to the issue of a high-octave string on the third course, are presented by the tuning instructions for the gittern in Selectissima elegantissimaque gallica italica et latina in guiterna ludenda carmina, published by Pierre Phalèse in 1570.