Still an approximation.
The miniwave's A to D generating a counter from a sawtooth wave addressing a
ROM is effectively the same as a 256x multiplier followed by a divider. But
since you cannot divide 256 equally by three the best you can do is
approximate. You would have two waves at 85 counts each followed by one at
86 counts. So the average is correct, but the timing of the clocks would
vary.
Two thirds of the time the pulses would be .13% short and one third of the
time the pulse would be .26% long.
I don't think you can do a perfect 3x multiplication, but the greater number
of binary multiplications followed by a counter/divider, the closer you
would get. The same thing using a wavetable. The greater the number of
samples per wave the closer to 3x you would get.
BTW if you think about it the 3x approximation would be equivalent to
applying a pulse wave with 33.3% duty cycle to the linear FM input on a VCO
tuned to 3x the fundamental. There would be sidebands generated. Whereas
using a 256x multiplier followed by a /85 divider would get you a proper
square wave, but with a frequency error of 1.2%.
Paul H.
----- Original Message -----
From: "mate_stubb" <mate_stubb@...>
To: <motm@yahoogroups.com>
Sent: Tuesday, January 03, 2006 9:58 PM
Subject: [motm] Re: External clock module
> The Miniwave does clock multiplication. Bank 7 of the standard ROM
> does binary rate multiplication from x2 up to x15. The only drawback
> is that there is only one output.
>
> Moe
> http://www.hotrodmotm.com
> http://www.wiseguysynth.com
>
> --- In motm@yahoogroups.com, Paul Haneberg <phaneber@o...> wrote:
>> Binary Multiplication = Not really easy, but doable - Multiply triangle
>> waves with precision rectifiers then convert to square waves
>> Integer Multiplication = Not impossible, but pretty stinkin hard -
>
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> Yahoo! Groups Links
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