The Pseudo-Octave

It might seem as if the octave is so fundamental, so much at the heart of all musical sound, that it would be nearly impossible to have music without it. In the TransFormSynth, a simple dial lets you retune the octave into a pseudo-octave. Don't be afraid, give it a try.

Used in conjunction with the timbre slider, it is possible for some non-octave intervals to appear very similar to the octave. The following figure shows how this can happen.



First, recall that in a harmonic tone (shown in blue at the bottom) every overtone of the octave (the green) lines up with one of the overtones of the root. In essence, the octave is contained in the root.

In the "stretched" tone at the top, the overtones have been expanded like the bellows of an accordian (in this case by a factor of 2.1). Instead of the octave with numerical value 2, this gives the "pseudo-octave" wth numerical value 2.1. Observe that the overtones are stretched so that every other overtone of the root (shown at the top in blue) aligns with an overtone of the pseudo-octave (shown in green). This coincidence of overtones causes the two sounds (a stretched tone and its pseudo-octave) to appear similar in the same way that a tone and its octave appear similar. This captures some of the effect or feel of an octave, without actually being an octave (i.e., a factor of 2).



Adjusting the pseudo-octave dial changes both the frequency of the octave (to make it a pseudo-octave) and the frequencies of all the overtones (to make them pseudo-harmonics!). The numerical value of the dial is shown below in cents (1200 cents is the usual octave).