[sdiy] Harmonic bandwidth

[John Mahoney]

At 11:14 AM 1/10/2008, Ben Lincoln wrote:

>...
>In terms of analogue sine wave oscillators, I have not built one yet (a
>kit or two is in my budget for next month), but I imagine there must be at
>least a couple of people on a DIY synth list that have 2 or more of them.
>How hard would it be to do a reliable phase offset?

Stating the obvious, first: It's easy to do a 180-degree inversion. 
That's not much to work with, though.

Most filters will induce some phase shift. "Phase shifter" effects 
use all pass filters to shift the phase (or is it to impart a group 
delay?), as everybody knows. So, VCFs and/or tone controls could be useful.

Another approach: generate the sines with a computer. You could 
filter them for purity, but then you'd need to allow for the filters' 
phase shift...

Finally, the shameless plug. ;-) A Mankato filter in self-oscillation 
produces 8 phase-shifted sine waves (so to speak). You'd want to 
carefully level match each output, for these experiments; they are 
close, but not precisely matched.

JPM 


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