LVM, was Re: [sdiy] PIC Quantizer project

[Tim Parkhurst]

Comments inline...

> -----Original Message-----
> From: john mahoney [mailto:jmahoney at gate.net]
> Sent: Monday, November 15, 2004 1:38 PM
> To: Tim Parkhurst; synth-diy at dropmix.xs4all.nl
> Subject: LVM, was Re: [sdiy] PIC Quantizer project
> 
> Welcome back, Servo! Don't get me wrong, but I could tell that you
> were away.
> ************************
I'm kind of like a good chorus box, you only notice I'm there because it
sounds so different when you shut me off ;) By the way (OT), I got a Dan
Electro "Cool Cat" chorus several months back ($30 on ebay), and finally got
a chance to try it out the other day... sweeeeeeeeeet sounding chorus! Maybe
the best stomp box chorus I've ever heard.


> > ... the New Generation of Low Voltage Modulars? (NGLVM or just
> > LVM if you prefer)
> 
> LVM works for me, although 5V isn't considered low voltage anymore.
>**************************
True, but I think one huge advantage of the monster +/-10V signals is that
it's so much easier to get a good signal to noise ratio. I think 5V is a
good compromise. Now maybe we'll be complaining about 5V as 'huge' in
another decade or so, but for right now, I think 5V signals makes things
easy to work with.
 
> 
> > ... or maybe 0 to +5V but centered around 2.5V, but that's another
> > argument/thread.
> 
> Seems like a good discussion to have. I don't think it would take a
> huge effort to design a 5V synth as compared to one using "standard"
> levels. One hard part is deciding how to do everything with 0 to 5V.
> How do you handle bi-polar signals? Use +/-2.5V and shift it to 0-5 as
> needed (like, where it meets a digipot)? But if you're going to do all
> that level shifting, maybe you don't save much. We need to examine all
> the voltage levels used in a synth. As others have said, filters don't
> use full-scale signals internally, anyway!
>*******************************
Well, the 'mono-polar' vs. bi-polar levels used on modulars has always
bugged me. I guess its necessary because you want something like an EG to
give you a one sided response (the VCF always opens up as the envelope
rises), while you want an LFO to give you a bi-polar response (modulate
around a center frequency, for example). How to accomplish this with a
signal that can still be passed through an IC only capable of handling 0 to
5V? I'm not sure how you'd pass a +/- 2.5V signal through a digi-pot powered
by GND and +5V. Or do you make everything 0 to 5V and have a mono-polar CV
input and a bi-polar CV input on your modules? Or???


> 
> > <blasphemy>
> > switching to 0.5V per octave instead of the 'traditional' 1V per
> octave.
> > Then we can still get a full 10 octaves out of the CV range.
> > </blasphemy>
> 
> Seems logical to me.
> --
> john (used to be a CAD geek, too -- now just a cad *and* a geek)
> 
***********************
I think going to 0.5V/octave is pretty necessary if we're going to be using
smaller signals. But then again, that's me ;)


Tim (smaller signals) Servo
 

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