Aligning Timbre with Tuning

The "principle of local consonance" says that sounds tend to be minimally dissonant when their overtones are maximally aligned. For some tunings, such as equal temperaments, this alignment can be done exactly while for others (think of a scale defined by an arbitrary collection of intervals) it can only be approximated. In either case, a simple approximation is to move all the overtones of the sound to the nearest scale step. This is the approach taken by the TransFormSynth when the tuning cannot be simply parameterized by a pair of generators (for example, the precise value of the pseudo-octave and the value of the scale step). This provides a concrete goal for the spectral mapping procedure and allows the matching of the timbre to the tuning to occur in an automatic (and hence nonintrusive) manner.

These ideas (and the principle of local consonance) were first described in an article called Relating Tuning and Timbre that appeared in Experimental Musical Instruments.