[sdiy] Timing : How close is close enough?

[Tom Arnold]

I realise that this has no proper answer, but....

A project I've been working on needs a clock.  For this particular project
I've been working on a simple 555 clock which will be fine.  Hardest part
has been getting it stable from .1 to 300hz while keeping it simple.

Anyhow, someones post made me start thinking about doing one digitally which
could be a useful module, esp if it did all the common timings ( .25ppwn,
.5ppwn, 1ppwn, 1ppqn etc etc

The question is, how close is close enough?  If I assume I'm going to set it
to something between .1bpm and 300bpm, even if I chose my cpu clock so its
sometimes a clean division, I'm going to be off by a little bit most of
the time.  Assuming I can service the timing loop 10000times a second my
error at 300bpm looks like it should be something less then .1% ( I say
"something less" as I did this in a spreadsheet to play with timings and I
dont have the sheet in front of me ).

I know this could devolve into a religious debate, but I'm curious what
people really think *is* close enough.  I mean, when you set that 909 to
130bpm, has anyone bothered to see how close it really is?  And yeah, I
realise that the point of building a timing module like this is so it
provides master timing for Everything so even if its off everything is off
by the same amount.

Anyhow, this is the kinda stuff I lay awake at night thinking about...

-- 
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 - Tom Arnold       -  Free Synth DIY webspace http://www.sdiy.org 
 - SynthGeek        -
 - BBD Fanatic      -  "...is it a virus, a drug, or a religion?" 
 - echo evho wjxo   -    Juanita Shrugs. "What's the difference?" 
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