[sdiy] Generating acyclic waveforms?

[Veronica Merryfield]

The effect is called harmonic sharpening and happens in all materials used for instruments.

The process goes something like this. Imagine a taught string. It has length and tension. When plucked, it vibrates. Looking only at the fundamental, the string lengthens at the extremes of the excursion as does the tension. The next harmonic is therefore subject to higher tension and longer length. And so on. The amount of sharpening peaks at the note start and then decays away. The effect is the same in woodwind and brass but tends to be less so since the material moves a lot less than a string. However, it is this subtle effect that gives say a trumpet it's characteristic sound that a simple oscillator synth can not reproduce.

This is one of the reasons I started looking at additive synthesis and the Synergy. I have tried to do this in the analogue world with several sine VCOs but it wasn't easy. Each one had an envelope generator for pitch and amplitude. It is not as computationally expensive to do in software or FPGA as it might seem - a few adds and a couple of table look ups for each sine osc. The other thing to realise is that you only need a few harmonics to make the sound seem real. Many of the Synergy patches use 3 to 5 oscillators per voices to sound very realistic.

Adding noise to the reset level in a VCO is not going to modulate the harmonic content over the duration of a note to mimic harmonic sharpening.

Veronica, currently working on a Synergy based AU