crap Synth idea-DIY

Clive Jones CJones at
Fri Mar 1 00:20:00 CET 1996

Hi Chaps

I've just been on Linear Devices Web page - take a look if you haven't   
been there already. The URL is;

JDM wrote

<keyboard scanner text deleted>

>I think you completely miss the point here - just because I have spent
>approximately 800 hours in the past year dealing with keyboard scanning   
>the programming of mono and polyphonic voice assignment algorithms, and   
>to voice my opinion on the usefulness of building your own keyboard   
>circuitry, doesn't mean that *you* can't go ahead and build one if you   
>you can obtain something from it.  Whether you can benefit from my   
>or not remains to be seen.

I don't want to be involved in a flame war on this point - *I* prefer to   
do stuff discreetly, sure I could write most of the analogue functions in   
code - but *I* would much rather do it in hardware.

I have to ask this somewhat Ironic question based on your initial   
response to my post - why are you re-writing the JP6 firmware? Can we see   
a spec on the firmware? Will it increase patch storage? Correct me if I'm   
wrong but I heard it was to improve the MIDI spec - is *that* worth the   
time and expense? I was contemplating updating the DSX to include MIDI,   
an 8 channel MIDI - CV converter and a MIDI interface for Obie's with the   
Computer Interface, but, after looking at the project from all angles, I   
can say that I don't really think it's worth it. I published the draft to   
AH sometime in November if my memory serves me correctly.

I'll let you into a little secret. I saw a couple of days ago an IC   
specifically designed to scan keyboards, it's fully polyphonic and has a   
serial interface that outputs MIDI data - the only external device needed   
was the clock oscillator - this is fabricated on a single chip!

>Detecting which keys are depressed are the easiest part of the problem.   

>Then you have to decide how to assign notes to a (presumably) limited
>number of voices.  Unison, rotating, nonrotating assignments - how are
>you going to do this in hardware?  These are difficult enough to
>implement in software.

You didn't read the original post correctly, the idea was to limit uP   
overhead using a self scanning keyboard to write the results to RAM - uP   
access would follow in the blanking period to read the results.

Can we let this thread die now? It's all about opinions and we could go   
on forever about this. Let me just make one point clear - my original   
post was an *idea* - some people may have obtained some ideas from it. I   
*do* get post from people saying that it's given *them* an idea to do   
something in a different manner, so in that respect it worked.

'll let you into another secret - I wouldn't do it like this either - I'd   
just make the keyboard scanning matrix part of the uP memory map and scan   
it during interrupt blanking - but *alot* of people on this list cannot   
design 8 or 16 bit CPU systems or write code - ever thought of that????


/<c.jones at> / ...and on the 8th day
/01344 850213 Work   / God made Synthesizers
/01344 850209/291 Fax/ ...and God was called
/01628 602106 Home   /   ' Tom Oberheim '

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