Since making some modfications to STS’ Harmonium last week, I’ve been experimenting with ways in which to slightly stretch the pure ratios of the harmonic frequencies, and listening to the timbral changes that result. Fortunately STS and Robert Syrett had already put together a Tiltatron that provided a good starting point for making adustments to the 16 values with a minimum of controls.
By reducing the range of some of the Tiltatron controls, fixing others, and adding a further offset control I manged to set up a controller that could give me the various ‘spread’ shapes I was after with just two parameters – the ‘shape’ control adjusts the intensity and direction of the curves, and the pivot point makes it possible to select a fixed harmonic around which the shape can fold. For example, a fixed root with gradualy increasing deviations as the harmonics increase, or vice versa. Or a central harmonic as a fixed point with deviations (up or down) towards the higher and lower frequencies.
I’ve posted a tryout patch on the Audulus forum. Rather than automating the spread and pivot I’ve left them standing for manual interaction. The option to invert the values for the even/odd harmonics can lead to some nice bell like tones, and the ‘scan’ row of controls on the Tiltatron provides a nice way of highlighting specific harmonics.
A next step could be to strip it all down and put together a compact module with only four controls. A shape and pivot for adjusting the frequencies of the harmonics, and a shape and pivot for adjusting their intensity.