[sdiy] A crazy idea..

[Fredrik Carlqvist]

Why not multiplex several control voltage channels into one with a synch
beat inbetween? Think composite video... 

Use one 4051 to select one control voltage channel at a time, output
with a brief '0' inbetween for synchronization. Perhaps clocked at
somwhere around 4kHz? Each control voltage then gets an update every 2
ms. 

The decoder uses another 4051 with storage capacitors and buffers on the
outputs and a counter trigged by the synch pulses. With a longer synch
pulse before the 'first' sample, the decoder counter can be reset so
that the channels map correctly. 

The synch pulses need to be 'large' compared to the data levels. But the
result should be an audio range signal, bypassing any capacitors in the
signal chain. 

I guess you could get around 10-12 bits of resolution in the decoder.


Fredrik C


 

-----Original Message-----
From: owner-synth-diy at dropmix.xs4all.nl
[mailto:owner-synth-diy at dropmix.xs4all.nl] On Behalf Of harrybissell
Sent: den 6 oktober 2005 03:46
To: Jeff Farr
Cc: Eric Honour; synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] A crazy idea..

You could use multichannel FM as well... but that would get kind of
tricky.
Switched capacitor filters would be a good choice here. But watch out,
as higher order filters carry their own problems like group delay etc.

Might be easier to do CV-midi conversion and record the data in
something like Cakewalk (or whatever you kids are using these days :^).
I used to stripe one channel with SMPTE time code and lock synths to
that. Po' man's multitrack.

H^) harry

Jeff Farr wrote:

> I was thinking about 8 bands per audio channel, starting around 16k on

> downward in octaves.  However, I realize this will take a steep BP 
> curve to decode so that there is enough headroom between bands for 
> good resolution, I'm not sure what kinds of slope can be easily 
> achieved but I imagine having 12 or 24db of  space for each octave may

> not be high enough for a good resolution 'decode'.
> On 10/5/05, Harry Bissell Jr <harrybissell at prodigy.net> wrote:
>
>      > On 10/4/05, Eric Honour <autophage at gmail.com > wrote:
>      > >
>      > > What about using a channel as one half of a
>      > vocoder?
>      > >
>      > > IE, one audio channel carries twenty different
>      > CV's by having twenty
>      > > different (harmonically unrelated) tones of
>      > varying amplitude... much like
>      > > the 'ghosting' technique previously mentioned, but
>      > not actually containing
>      > > usable audio (it'd just sound like a crappy
>      > dissonant chord) - then using a
>      > > series of very narrow bandpass filters into a
>      > bunch of envelope followers?
>
>      You don't need 'harmonically unrelated' tones if you
>      are using sine waves (which have no harmonics). The
>      limiting factor would be how steep you can make the
>      bandpass filters... and how stable the recording
>      method is (wow, flutter, speed changes ?)
>
>      The lower audio tones will STILL be much slower to
>      recover.  I'd think that twenty tones would be really
>      pushing the limits of what you could do with practical
>      bandpass filters...
>
>      H^) harry
>