[sdiy] Controller design

[Tom Wiltshire]

Further to what was said earlier about whether to generate the oscillator output with a VCO or digitally, I'd just like to mention that a triangle is a good signal to produce digitally. It's very easy to generate, since you don't need any waveform look-up. All you need is a phase counter to which you add the frequency increment every sample. For the output sample, just use the phase (or the highest bits of it) and simply flip the phase for the second half of the waveform.
Furthermore the heavily limited harmonics reduce the potential impact of aliasing until you start trying to generate very high frequencies. Given the simplicity of the generation, it is easy to keep sample rates high. The only problem is how to (cheaply) output the samples with sufficient resolution and speed. A simple R-2R DAC might be best.

What range does your oscillator need to cover?

On 31 Dec 2015, at 10:58, Thomas Burdick <thomas at burdick.fr> wrote:

> The VCO I've put together has a triangle core, and a pulse derived from it. Changing the pulse width from about 30-90% (or 15-45% run cycle) and changing the mix from about 50/50 triangle/pulse to almost 100% pulse gives a nice range of metal-reed sounds. I'm encouraged by the sounds of what I've breadboarded so far, but I need to get a more sophisticated controller (I currently have 20 switches and a pot) before I can make any more decisions about the synth itself.
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