[sdiy] DCO theory

GothGeek SysAdmin xyzzy at sysabend.org
Tue Jun 18 01:14:34 CEST 2002


On Mon, Jun 17, 2002 at 04:02:11PM -0700, phillip m gallo wrote:
> -->Using the JX3P for example:  A fixed Hi-Freq LC oscillator is input to a
> Timer/Counter Chip (i8253) a count is programmed into the timer (correlating
> to the "Note" frequency") that will cause the chip to output a short pulse
> when the count is exhausted and the Timer Reloaded.  This pulse is used to
> "reset" the standard sawtooth integrator circuit. Since 16 bit's won't span
> the entire freq. range of interest, the ref osc is divided a few times to
> allow some "agility" across octaves.  Two oscillators implement per "Voice"
> and they each have their own Timer but are fed the same ref osc/fz division
> so they can only be "detuned" from each other but do not differ beyond the
> value that can be input into the timer (16 bits).

I havent thrown one of my Rolands on a scope yet ( may do that tonight ) but
wouldnt this make a choppy malformed sawtooth?  Wait. You said Sawtooth not
triangle.  I'd still think that you couldnt get a clean waveform this way
or maybe I'm just not groking this yet.


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