[sdiy] Midi oscillator!!

[Tom Wiltshire]

On 15 Jul 2008, at 20:05, Samppa Tolvanen wrote:

> I know midi is 31.25k Bauds a second, but You can divide all the  
> important
> frequencies from that, right?

No, not really. The Juno 106 uses what is basically a divider-based  
oscillator for its DCO, but it clocks it at 1MHz in the worst case,  
and at 4MHz in the higher range. A shade over 31KHz isn't even close.

You won't have anything like enough frequency accuracy as you go up  
the range. Think about the number of steps in each octave:

Octave 1:  31250 / 1000 = 31.25Hz
Octave 2:  31250 / 500 = 62.5Hz
Octave 3:  31250 / 250 = 125Hz
Octave 4:  31250 / 125 = 250Hz
Octave 5:  31250 / 62 = 504Hz
Octave 6:  31250 / 31 = 1008Hz

As you can see, there are 500 hundred different frequencies I can  
generate in Octave 1, but only 250 in octave 2. This gets worse as I  
go up, until I only have 31 frequencies in octave 5. It'd be nice if  
these lined up with quarter tones, but they won't. On top of that,  
errors in the division creep in by octave 5, where the true value  
should be 62.5, but I have to divide by 62.

> I'm not looking at making any existing solution obsolite

No, you're not!

Regards,
Tom