[sdiy] BBD tweaking (was: CV BBD)

[Tom Wiltshire]

> If i underclock, will i get a bad-quality sounding
> delay or will i just get really strange artefacts? Is
> there any lower limit for it to even work? I'm using a
> mn3005 and it's specified to 10kHz as the lowest clock
> speed, but that i'm guessing is with preserved
> quality.

I've played with the low-voltage MN series chips, and I know you can 
underclock them dramatically. I've had a 2 second delay out of a 1024 
stage device! Obviously at that sort of sampling frequency, the output 
result is a mess, and doesn't have much to do with the input.

> What about overclocking? I know there was a thread
> about it a while ago, the last post i found in the
> archive stated 409,600 Hz for the MN3005 - any news on
> that?

Overclocking is harder - you rapidly just hit the limit of the chips, 
and the sound stops coming out, at least for the low voltage chips.
I expect the limit is the resistance of the internal CMOS switches, 
which must limit how fast the next bucket's capacitor can charge.
The higher voltage chips may well have a lower switch resistance and 
hence be able to go faster.

I never killed a BBD by trying it, so give it a whirl, although I did 
kill a MN series clock chip by feeding it with external control 
voltage.

Regards,
Tom

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